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CLIMATE CHANGE

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The Earth is the only planet in our solar system that supports life. The complex process of evolution occurred on Earth only because of some unique environmental and climatic conditions that were present: water, an oxygen-rich atmosphere, and a suitable surface temperature. Mercury and Venus, the two planets that lie between Earth and the sun, do not support life. This is because Mercury has no atmosphere and therefore becomes very hot during the day, while temperatures at night may reach -140ºC. Venus, has a thick atmosphere which traps more heat than it allows to escape, making it too hot (between 150 and 450ºC) to sustain life. Only the Earth has an atmosphere of the proper depth and chemical composition. About 30% of incoming energy from the sun is reflected back to space while the rest reaches the earth, warming the air, oceans, and land, and maintaining an average surface temperature of about 15ºC.

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Weather & Climate  Weather is the combination of events in the atmosphere and climate is the overall accumulated weather in a certain location.  Over historic time spans there are a number of static variables that determine climate, including: latitude, altitude, proportion of land to water, and proximity to oceans and mountains.  Other climate determinants are more dynamic: The thermohaline circulation of the ocean distributes heat energy between the equatorial and Polar Regions; other ocean currents do the same between land and water on a more regional scale.  Degree of vegetation coverage affects solar heat absorption, water retention, and rainfall on a regional level.  Alterations in the quantity of atmospheric greenhouse gases determine the amount of solar energy retained by the planet, leading to global warming or global cooling.

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Atmosphere The chemical composition of the atmosphere is also responsible for nurturing life on our planet. Most of it is nitrogen (78%); about 21% is oxygen, which all animals need to survive; and only a small percentage (0.036%) is made up of carbon dioxide which plants require for photosynthesis. The atmosphere carries out the critical function of maintaining life-sustaining conditions on Earth, in the following way:  Each day, energy from the sun (largely in the visible part of the spectrum, but also some in the ultraviolet and infrared portions) is absorbed by the land, seas, mountains, etc.  If all this energy were to be absorbed completely, the earth would gradually become hotter and hotter. But actually, the earth both absorbs and, simultaneously releases it in the form of infrared waves (which cannot be seen by our eyes but can be felt as heat, for example the heat that you can feel with your hands over a heated car engine).  All this rising heat is not lost to space, but is partly absorbed by some gases present in very small (or trace) quantities in the atmosphere, called GHGs (greenhouse gases).  Greenhouse gases (for example, carbon dioxide, methane, nitrous oxide, water vapor, ozone) re-emit some of this heat to the earth's surface. If they did not perform this useful function, most of the heat energy would escape, leaving the earth cold (about -18 ºC) and unfit to support life.  However, ever since the Industrial Revolution began about 150 years ago, man-made activities have added significant quantities of GHGs to the atmosphere. The atmospheric concentrations of carbon dioxide, methane, and nitrous oxide have grown by about 31%, 151% and 17%, respectively, between 1750 and 2000.  An increase in the levels of GHGs could lead to greater warming, which, in turn, could have an impact on the world's climate, leading to the phenomenon known as climate change. th  Indeed, scientists have observed that over the 20 century, the mean global surface temperature increased by 0.6 °C (IPCC Report).  Climate model projections were summarized in the 2013 Fifth Assessment Report (AR5) by the Intergovernmental Panel on Climate Change (IPCC).  They indicated that during the 21st century the global surface temperature is likely to rise a further 0.3 to 1.7 °C (0.5 to 3.1 °F) for their lowest emissions scenario using stringent mitigation and 2.6 to 4.8 °C (4.7 to 8.6 °F) for their highest. Climate change therefore refers to a “statistically significant variation in either the mean state of the climate or in its variability, persisting for an extended period (typically decades or longer)”. Climate change may be due to natural internal processes or external forces, or to persistent anthropogenic changes in the composition of the atmosphere or in land use.

CAUSES OF CLIMATE CHANGE

The earth's climate is dynamic and always changing through a natural cycle. The causes of climate change can be divided into two categories - those that are due to natural causes and those that are created by man. NATURAL CAUSES

There are a number of natural factors responsible for climate change. Some of the more prominent ones are continental drift, volcanoes, ocean currents, the earth's tilt, and comets and meteorites.

Continental Drift  About 200 million years ago, the continents were all part of one large landmass. The continents were formed when the landmass began gradually drifting apart, millions of years back. This drift also had an impact on the climate because it changed the physical features of the landmass, their position and the position of water bodies.  The separation of the landmasses changed the flow of ocean currents and winds, which affected the climate. This drift of the continents continues even today; the Himalayan range is rising by about 1 mm (millimeter) every year because the Indian land mass is moving towards the Asian land mass, slowly but steadily.

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External forcing mechanisms  Slight variations in Earth's orbit lead to changes in the seasonal distribution of sunlight reaching the Earth's surface and how it is distributed across the globe.  The three types of orbital variations are variations in Earth's eccentricity, changes in the tilt angle of Earth's axis of rotation, and precession of Earth's axis.  Combined together, these produce Milankovitch cycles which have a large impact on climate and are notable for their correlation to glacial and interglacial periods, their correlation with the advance and retreat of the Sahara, and for their appearance in the stratigraphic record.  Milankovitch cycles drove the ice age cycles; CO2 followed temperature change "with a lag of some hundreds of years"; and that as a feedback amplified temperature change.  The depths of the ocean have a lag time in changing temperature (thermal inertia on such scale). Upon seawater temperature change, the solubility of CO2 in the oceans changed, as well as other factors impacting air-sea CO2 exchange.

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Solar intensity variations are considered to have been influential in triggering the Little Ice Age, and some of the warming observed from 1900 to 1950. Solar radiation increases from cyclical sunspot activity affecting global warming, and climate may be influenced by the sum of all effects (solar variation, anthropogenic radiative forcings, etc.). In an Aug 2011 CERN announced the publication of its CLOUD experiment. The results indicate that ionisation from cosmic rays significantly enhances aerosol formation in the presence of sulphuric acid and water, but in the lower atmosphere where ammonia is also required, this is insufficient to account for aerosol formation and additional trace vapours must be involved.

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The Earth's Tilt  The earth makes one full orbit around the sun each year. It is tilted at an angle of 23.5° to the perpendicular plane of its orbital path. For one half of the year when it is summer, the northern hemisphere tilts towards the sun. In the other half when it is winter, the earth is tilted away from the sun. If there was no tilt we would not have experienced seasons. Changes in the tilt of the earth can affect the severity of the seasons- more tilt means warmer summers and colder winters; less tilt means cooler summers and milder winters.  The Earth's orbit is somewhat elliptical, which means that the distance between the earth and the Sun varies over the course of a year. We usually think of the earth's axis as being fixed, after all, it always seems to point toward Polaris (also known as the Pole Star and the North Star). Actually, it is not quite constant: the axis does move, at the rate of a little more than a halfdegree each century.  So Polaris has not always been, and will not always be, the star pointing to the North. When the pyramids were built, around 2500 BC, the pole was near the star Thuban (Alpha Draconis). This gradual change in the direction of the earth's axis, called precession is responsible for changes in the climate.

Solar output  The sun is the predominant source for energy input to the Earth. Both long- and short-term variations in solar intensity are known to affect global climate.  Three to 4 billion years ago the sun emitted only 70% as much power as it does today. Over the 4 billion years, the energy output of the sun increased and atmospheric composition changed.  The Great Oxygenation Event -oxygenation of the atmosphere- around 2.4 billion years ago was the most notable alteration.  Over the next five billion years the sun's ultimate death as it becomes a red giant and then a white dwarf will have large effects on climate, with the red giant phase possibly ending any life on Earth that survives until that time.

Plate tectonics  Over the course of millions of years, the motion of tectonic plates reconfigures global land and ocean areas and generates topography. This can affect both global and local patterns of climate and atmosphere-ocean circulation.  The position of the continents determines the geometry of the oceans and therefore influences patterns of ocean circulation.

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The locations of the seas are important in controlling the transfer of heat and moisture across the globe, and therefore, in determining global climate. A recent example of tectonic control on ocean circulation is the formation of the Isthmus of Panama about 5 million years ago, which shut off direct mixing between the Atlantic and Pacific Oceans. This strongly affected the ocean dynamics of what is now the Gulf Stream and may have led to Northern Hemisphere ice cover. The size of continents is also important. Because of the stabilizing effect of the oceans on temperature, yearly temperature variations are generally lower in coastal areas than they are inland. A larger supercontinent will therefore have more area in which climate is strongly seasonal than will several smaller continents or islands.

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Volcanoes  When a volcano erupts it throws out large volumes of sulphur dioxide (SO 2), water vapour, dust, and ash into the atmosphere. Although the volcanic activity may last only a few days, yet the large volumes of gases and ash can influence climatic patterns for years. Millions of tonnes of sulphur dioxide gas can reach the upper levels of the atmosphere (called the stratosphere) from a major eruption.  The gases and dust particles partially block the incoming rays of the sun, leading to cooling. Sulphur dioxide combines with water to form tiny droplets of sulphuric acid. These droplets are so small that many of them can stay aloft for several years.  They are efficient reflectors of sunlight, and screen the ground from some of the energy that it would ordinarily receive from the sun. Winds in the upper levels of the atmosphere, called the stratosphere, carry the aerosols rapidly around the globe in either an easterly or westerly direction. (Course Book by BestCurrentAffairs.com)  Mount Pinatoba, in the Philippine islands erupted in April 1991 emitting thousands of tonnes of gases into the atmosphere. Volcanic eruptions of this magnitude can reduce the amount of solar radiation reaching the Earth's surface, lowering temperatures in the lower levels of the atmosphere (called the troposphere), and changing atmospheric circulation patterns.

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Ocean variability  The oceans are a major component of the climate system. They cover about 71% of the Earth and absorb about twice as much of the sun's radiation as the atmosphere or the land surface. Ocean currents move vast amounts of heat across the planet roughly the same amount as the atmosphere does. But the oceans are surrounded by land masses, so heat transport through the water is through channels.  Short-term fluctuations (years to a few decades) such as the El Niño-Southern Oscillation, the Pacific decadal oscillation, the North Atlantic oscillation, and the Arctic oscillation, represent climate variability rather than climate change.  Winds push horizontally against the sea surface and drive ocean current patterns. Certain parts of the world are influenced by ocean currents more than others. The coast of Peru and other adjoining regions are directly influenced by the Humboldt Current that flows along the coastline of Peru. The El Nino event in the Pacific Ocean can affect climatic conditions all over the world.  On longer time scales, alterations to ocean processes such as thermohaline circulation play a key role in redistributing heat by carrying out a very slow and extremely deep movement of water, and the long-term redistribution of heat in the world's oceans.  Ocean currents have been known to change direction or slow down. Much of the heat that escapes from the oceans is in the form of water vapor, the most abundant greenhouse gas on Earth. Yet, water vapor also contributes to the formation of clouds, which shade the surface and have a net cooling effect.  Any or all of these phenomena can have an impact on the climate, as is believed to have happened at the end of the last Ice Age, about 14,000 years ago. THE INFLUENCES OF HUMAN ACTIVITY ON CLIMATE

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Human activity has influenced global surface temperatures by changing the radiative balance governing the Earth on various timescales and at varying spatial scales. The most profound and well-known anthropogenic influence is the elevation of concentrations of greenhouse gases in the atmosphere. Humans also influence climate by changing the concentrations of aerosols and ozone and by modifying the land cover of Earth’s surface.

The natural greenhouse effect:  The sun's radiation, much of it in the visible region of the spectrum, warms our planet. On average, earth must radiate back to space the same amount of energy which it gets from the sun.  Being cooler than the sun, earth radiates in the infrared. (An object, when getting warmer, radiates more energy and at shorter wavelengths. On cooling, it emits less and at longer wavelengths. (Lava or heated iron is examples.)  The wavelengths at which the sun and the earth emit are, for energetic purposes, almost completely distinct. Often, solar radiation is called shortwave, whereas terrestrial infrared is called long wave radiation.  Greenhouse gases in earth's atmosphere, while largely transparent to incoming solar radiation, absorb most of the infrared emitted by earth's surface.  The air is cooler than the surface, emission declines with temperature, so the air or, rather, its greenhouse gases emit less infrared upwards than the surface. Moreover, while the surface emits upwards only, the air's greenhouse gases radiate both up- and downwards, so some infrared comes back down.  Clouds also absorb infrared well. Again, cloud tops are usually cooler and emit less infrared upwards than the surface, while cloud bottoms radiate some infrared back down. All in all, part of the infrared emitted by the surface gets trapped.  Satellites tell us that the amount of infrared going out to space corresponds to an `effective radiating temperature’ of about -18 ° C.  At -18 ° C, about 240 watts per square metre (W/m) of infrared are emitted. This is just enough to balance the absorbed solar radiation.  Yet earth's surface currently has a mean temperature near 15°C and sends an average of roughly 390 W/m of infrared upwards.  After the absorption and emission processes just outlined, 240 W/m eventually escape to space; the rest is captured by greenhouse gases and clouds.  The `natural greenhouse effect' can be defined as the 150 or so W/m of outgoing terrestrial infrared trapped by earth's preindustrial atmosphere.

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It warms earth's surface by about 33 ° C. As an aside, note that garden glasshouses retain heat mainly by lack of convection and advection. Under clear sky, roughly 60-70 % of the natural greenhouse effect is due to water vapor, which is the dominant greenhouse gas in earth's atmosphere. Next important is carbon dioxide, followed by methane, ozone, and nitrous oxide. Clouds are another big player in the game. Please don't confuse clouds with water vapor: clouds consist of water droplets or ice particles or both. Under cloudy sky the greenhouse effect is stronger than under clear sky. At the same time, cloud tops in the sunshine look brilliantly white: they reflect sunlight.  Globally and seasonally averaged, clouds currently exert the following effects: Outgoing terrestrial infrared trapped (warming) about 30 W/m  Solar radiation reflected back to space (cooling) nearly 50 W/m  Net cloud effect (cooling roughly 20 W/m Earth's present reflectivity or albedo (whiteness) is near 0.3. This means that about 30% or slightly over 100 W/m of the sun's incoming radiation is reflected back to space, while roughly 240 W/m or about 70 % is absorbed. Almost half of earth's current albedo and around 20 % of the natural greenhouse effect is caused by clouds. Globally averaged, the surface constantly gains radiative energy, whereas the atmosphere scores a loss. Sending up about 390 W/m, the surface absorbs roughly 170 W/m solar radiations and over 300 W/m infrared back radiations from greenhouse gases and clouds. The atmosphere, clouds included, radiates both up-and downwards, altogether over 500 W/m. It absorbs roughly 70 W/m solar radiation and 350 W/m terrestrial infrared. The surface's radiative heating and the atmosphere's radiative cooling are balanced by convection and by evaporation followed by condensation. When evaporating, water takes up latent heat; when water vapor condenses, as happens in cloud formation, latent heat is released to the atmosphere.

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IPCC LIST OF GREENHOUSE GASES Gases relevant to radiative forcing only (as per IPCC documentation) Alternate Name

Carbon dioxide

Carbonic anhydride

(CO2)

365 μmol/mol

87 μmol/mol

Carbon Monoxide

Carbonic Oxide

(CO)

11.1 μmol/mol

46 nmol/mol

Marsh gas Laughing gas Carbon tetrafluoride

(CH4) (N2O) (CF4)

1,745 nmol/mol 314 nmol/mol 80 pmol/mol

1,045 nmol/mol 44 nmol/mol 40 pmol/mol

Methane Nitrous oxide Tetrafluoromethane

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Gas

Formula

1998 Level

Increase since 1750

Perfluoroethane

(C2F6)

3 pmol/mol

Sulfur hexafluoride

Sulfur fluoride

(SF6)

4.2 pmol/mol

HFC-23 HFC-134a

Trifluoromethane 1,1,1,2tetrafluoroethane

(CHF3) 0.001(C2H2F4)

14 pmol/mol 7.5 pmol/mol

HFC-152a

1,1-Difluoroethane

(C2H4F2)

0.5 pmol/mol

Hexafluoroethane

GASES RELEVANT TO RADIATIVE FORCING AND OZONE DEPLETION (AS PER IPCC DOCUMENTATION) Gas CFC-11§ CFC-12§ CFC-13§ CFC-113 CFC-114 CFC-115 Carbon tetrachloride

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Alternate Name Trichlorofluoromethane Dichlorodifluoromethane Chlorotrifluoromethane 1,1,1-Trichlorotrifluoroethane 1,2-Dichlorotetrafluoroethane Chloropentafluoroethane Tetrachloromethane

Formula (CFCl3) (CF2Cl2) (CClF3) (C2F3Cl3) (C2F4Cl2) (C2F5Cl) (CCl4)

1998 Level 268 pmol/mol 533 pmol/mol 4 pmol/mol 84 pmol/mol 15 pmol/mol 7 pmol/mol 102 pmol/mol

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Increase since 1750 268 pmol/mol 533 pmol/mol 4 pmol/mol 84 pmol/mol 15 pmol/mol 7 pmol/mol 102 pmol/mol

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Water vapour:  Water vapour is the most potent of the greenhouse gases in Earth’s atmosphere, but its behaviour is fundamentally different from that of the other greenhouse gases.  The primary role of water vapour is not as a direct agent of radiative forcing but rather as a climate feedback—that is, as a response within the climate system that influences the system’s continued activity.  This distinction arises from the fact that the amount of water vapour in the atmosphere cannot, in general, be directly modified by human behaviour but is instead set by air temperatures.  The warmer the surface, the greater the evaporation rate of water from the surface.  As a result, increased evaporation leads to a greater concentration of water vapour in the lower atmosphere capable of absorbing longwave radiation and emitting it downward.

[BestCurrentAffairs.com's Book for IAS Prelims 2022] 1,1,1-Trichloroethane HCFC-141b HCFC-142b Halon-1211 Halon-1301

Methyl chloroform 1,1-Dichloro-1-Fluoroethane 1-Chloro-1,1-Difluoroethane Bromochlorodifluoromethane Bromotrifluoromethane

(CH3CCl3) (C2H3FCl2) (C2H3F2Cl) (CClF2Br) (CF3Br)

69 pmol/mol 10 pmol/mol 11 pmol/mol 3.8 pmol/mol 2.5 pmol/mol

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CARBON DIOXIDE:  Of the greenhouse gases, carbon dioxide (CO2) is most significant.  Natural sources of atmospheric CO2 include outgassing from volcanoes, the combustion and natural decay of organic matter, and respiration by aerobic (oxygen-using) organisms.  These sources are balanced, on average, by a set of physical, chemical, or biological processes, called “sinks,” that tend to remove CO2 from the atmosphere. Significant natural sinks include terrestrial vegetation, which takes up CO2 during the process of photosynthesis.  A number of oceanic processes also act as carbon sinks. One such process, called the “solubility pump,” involves the descent of surface sea water containing dissolved CO2.  Another process, the “biological pump,” involves the uptake of dissolved CO2 by marine vegetation and phytoplankton (small, free-floating, photosynthetic organisms) living in the upper ocean or by other marine organisms that use CO2 to build skeletons and other structures made of calcium carbonate (CaCO3).  As these organisms expire and fall to the ocean floor, the carbon they contain is transported downward and eventually buried at depth. A long-term balance between these natural sources and sinks leads to the background, or natural, level of CO2 in the atmosphere.  In contrast, human activities increase atmospheric CO2 levels primarily through the burning of fossil fuels (principally oil and coal, and secondarily natural gas, for use in transportation, heating, and the generation of electrical power) and through the production of cement.  Other anthropogenic sources include the burning of forests and the clearing of land.  Anthropogenic emissions currently account for the annual release of about 7 gigatons (7 billion tons) of carbon into the atmosphere.  Anthropogenic emissions are equal to approximately 3% of the total emissions of CO2 by natural sources, and this amplified carbon load from human activities far exceeds the offsetting capacity of natural sinks (by perhaps as much as 2–3 gigatons per year).  CO2 has consequently accumulated in the atmosphere at an average rate of 1.4 parts per million (ppm) by volume per year and now this rate of accumulation has been linear (that is, uniform over time).  However, certain current sinks, such as the oceans, could become sources in the future. This may lead to a situation in which the concentration of atmospheric CO2 builds at an exponential rate.  The natural background level of carbon dioxide varies on timescales of millions of years due to slow changes in out gassing through volcanic activity.  Radiative forcing caused by carbon dioxide varies in an approximately logarithmic fashion with the concentration of that gas in the atmosphere.  The logarithmic relationship occurs as the result of a saturation effect wherein it becomes increasingly difficult, as CO2 concentrations increase, for additional CO2 molecules to further influence the “infrared window” (a certain narrow band of wavelengths in the infrared region that is not absorbed by atmospheric gases).  The logarithmic relationship predicts that the surface warming potential will rise by roughly the same amount for each doubling of CO2 concentration.  At current rates of fossil-fuel use, a doubling of CO2 concentrations over preindustrial levels is expected to take place by the middle of the 21st century (when CO2 concentrations are projected to reach 560 ppm).  A doubling of CO2 concentrations would represent an increase of roughly 4 watts per square metre of radiative forcing. Given typical estimates of “climate sensitivity” in the absence of any offsetting factors, this energy increase would lead to a warming of 2 to 5 °C (3.6 to 9 °F) over preindustrial time.  The total radiative forcing by anthropogenic CO2 emissions since the beginning of the industrial age is approximately 1.66 watts per square metre.

METHANE:  Methane (CH4) is the second most important greenhouse gas.  CH4 is more potent than CO2 because the radiative forcing produced per molecule is greater.  In addition, the infrared window is less saturated in the range of wavelengths of radiation absorbed by CH4, so more molecules may fill in the region.  However, CH4 exists in far lower concentrations than CO2 in the atmosphere, and its concentrations by volume in the atmosphere are generally measured in parts per billion (ppb) rather than ppm.  CH4 also has a considerably shorter residence time in the atmosphere than CO2 (the residence time for CH4 is roughly 10 years, compared with hundreds of years for CO2).  Natural sources of methane include tropical and northern wetlands, methane-oxidizing bacteria that feed on organic material consumed by termites, volcanoes, seepage vents of the seafloor in regions rich with organic sediment, and methane hydrates trapped along the continental shelves of the oceans and in polar permafrost.  The primary natural sink for methane is the atmosphere itself, as methane reacts readily with the hydroxyl radical (OH-) within the troposphere to form CO2 and water vapour (H2O). When CH4 reaches the stratosphere, it is destroyed.  Another natural sink is soil, where methane is oxidized by bacteria.  As with CO2, human activity is increasing the CH4 concentration faster than it can be offset by natural sinks.  Anthropogenic sources currently account for approximately 70% of total annual emissions, leading to substantial increases in concentration over time.  The major anthropogenic sources of atmospheric CH4 are rice cultivation, livestock farming, the burning of coal and natural gas, the combustion of biomass, and the decomposition of organic matter in landfills.  The net radiative forcing by anthropogenic CH4 emissions is approximately 0.5 watt per square metre—or roughly one-third the radiative forcing of CO2.

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About ¼ of all methane emissions are said to come from domesticated animals such as dairy cows, goats, pigs, buffaloes, camels, horses, and sheep. These animals produce methane during the cud-chewing process. Methane is also released from rice or paddy fields that are flooded during the sowing and maturing periods. When soil is covered with water it becomes anaerobic or lacking in oxygen. Under such conditions, methane-producing bacteria and other organisms decompose organic matter in the soil to form methane. Nearly 90% of the paddy-growing area in the world is found in Asia, as rice is the staple food there. China and India, between them, have 80-90% of the world's rice-growing areas. Methane is also emitted from landfills and other waste dumps. If the waste is put into an incinerator or burnt in the open, carbon dioxide is emitted. Methane is also emitted during the process of oil drilling, coal mining and also from leaking gas pipelines (due to accidents and poor maintenance of sites). Electricity is the main source of power in urban areas. All our gadgets run on electricity generated mainly from thermal power plants. These thermal power plants are run on fossil fuels (mostly coal) and are responsible for the emission of huge amounts of greenhouse gases and other pollutants. Cars, buses, and trucks are the principal ways by which goods and people are transported in most of our cities. These are run mainly on petrol or diesel, both fossil fuels. We generate large quantities of waste in the form of plastics that remain in the environment for many years and cause damage. We use a huge quantity of paper in our work at schools and in offices- Timber is used in large quantities for construction of houses, which means that large areas of forest have to be cut down.

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SURFACE-LEVEL OZONE AND OTHER COMPOUNDS:  The next most significant greenhouse gas is surface, or low-level, ozone (O3).  Surface O3 is a result of air pollution; it must be distinguished from naturally occurring stratospheric O3, which has a very different role in the planetary radiation balance.  The primary natural source of surface O3 is the subsidence of stratospheric O3 from the upper atmosphere. In contrast, the primary anthropogenic source of surface O3 is photochemical reactions involving the atmospheric pollutant carbon monoxide (CO).  The best estimates of the concentration of surface O3 are 50 ppb, and the net radiative forcing due to anthropogenic emissions of surface O3 is approximately 0.35 watt per square metre.

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NITROUS OXIDES AND FLUORINATED GASES:  Additional trace gases produced by industrial activity that have greenhouse properties include nitrous oxide (N2O) and fluorinated gases (halocarbons), the latter including sulfur hexafluoride, hydrofluorocarbons (HFCs), and perfluorocarbons (PFCs).  Nitrous oxide is responsible for 0.16 watt per square metre radiative forcing, while fluorinated gases are collectively responsible for 0.34 watt per square metre.  Nitrous oxides have small background concentrations due to natural biological reactions in soil and water, whereas the fluorinated gases owe their existence almost entirely too industrial sources.  A large amount of nitrous oxide emission has been attributed to fertilizer application. This in turn depends on the type of fertilizer that is used, how and when it is used and the methods of tilling that are followed. Contributions are also made by leguminous plants, such as beans and pulses that add nitrogen to the soil.

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HYDROFLUOROCARBONS (HFCS):  The HFCs with the largest measured atmospheric abundances are (in order), HFC-23 (CHF3), HFC-134a (CF3CH2F), and HFC-152a (CH3CHF2).  HFC-23 is a by-product of HCFC-22 production. It has a long atmospheric lifetime of 260 years, so that most emissions, which have occurred over the past two decades, will have accumulated in the atmosphere.  Between 1978 and 1995, HFC-23 increased from about 3 to 10 ppt; and it continues to rise even more rapidly.  HFC-134a is used primarily as a refrigerant, especially in car air conditioners. It has an atmospheric lifetime of 13.8 years, and its annual emissions have grown from near zero in 1990 to an estimated 0.032 Tg/yr in 1996.  The abundance continues to rise almost exponentially as the use of this HFC increases.  HFC-152a is a short-lived gas with a mean atmospheric lifetime of 1.4 years. Its rise has been steady, but its low emissions and a short lifetime have kept its abundance below 1 ppt.

PERFLUOROCARBONS (PFCS) AND SULPHUR HEXAFLUORIDE (SF6):  PFCs, in particular CF4 and C2F6, as well as SF6 have sources predominantly in the Northern Hemisphere, atmospheric lifetimes longer than 1,000 years, and large absorption cross-sections for terrestrial infra-red radiation.  These compounds are far from a steady state between sources and sinks, and even small emissions will contribute to radiative forcing over the next several millennia.  Current emissions of C2F6 and SF6 are clearly anthropogenic and well quantified by the accumulating atmospheric burden.  CF4 and SF6 are naturally present in fluorites, and out-gassing from these materials leads to natural background abundances of 40 ppt for CF4 and 0.01 ppt for SF6.  However, at present the anthropogenic emissions of CF4 exceed the natural ones by a factor of 1,000 or more and are responsible for the rapid rise in atmospheric abundance.  The only important sinks for PFCs and SF6 are photolysis or ion reactions in the mesosphere. These gases provide useful tracers of atmospheric transport in both troposphere and stratosphere.  A new, long-lived, anthropogenic greenhouse gas has recently been found in the atmosphere. Trifluoromethyl sulphur pentafluoride (SF5CF3) - a hybrid of PFCs and SF6 not specifically addressed in Annex A of the Kyoto Protocol - has the largest radiative forcing, on a per molecule basis, of any gas found in the atmosphere to date. Its abundance has grown from near zero in the late 1960s to about 0.12 ppt in 1999.

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CARBON MONOXIDE (CO):  Carbon monoxide (CO) does not absorb terrestrial infrared radiation strongly enough to be counted as a direct greenhouse gas, but its role in determining tropospheric OH indirectly affects the atmospheric burden of CH4 and can lead to the formation of O3.  More than half of atmospheric CO emissions today are caused by human activities, and as a result the Northern Hemisphere contains about twice as much CO as the Southern Hemisphere.  Because of its relatively short lifetime and distinct emission patterns, CO has large gradients in the atmosphere, and its global burden of about 360 Tg is more uncertain than those of CH4 or N2O.  In the high northern latitudes, CO abundances vary from about 60 ppb during summer to 200 ppb during winter.  At the South Pole, CO varies between about 30 ppb in summer and 65 ppb in winter.  Observed abundances, supported by column density measurements, suggest that globally, CO was slowly increasing until the late 1980s, but has started to decrease since then possibly due to decreased automobile emissions as a result of catalytic converters.  Anthropogenic sources (deforestation, savanna and waste burning, fossil and domestic fuel use) dominate the direct emissions of CO, emitting 1,350 out of 1,550 Tg(CO)/yr.  A source of 1,230 Tg(CO)/yr is estimated from in situ oxidation of CH4 and other hydrocarbons, and about half of this source can be attributed to anthropogenic emissions.

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HYDROGEN (H2):  Molecular hydrogen (H2) is not a direct greenhouse gas. But it can reduce OH and thus indirectly increase CH4 and HFCs. Its atmospheric abundance is about 500 ppb.  H2 is produced in many of the same processes that produce CO (e.g., combustion of fossil fuel and atmospheric oxidation of CH4), and its atmospheric measurements can be used to constrain CO and CH4 budgets.  Due to the larger land area in the Northern Hemisphere than in the Southern Hemisphere, most H2 is lost in the Northern Hemisphere. As a result, H2 abundances are on average greater in the Southern Hemisphere despite 70% of emissions being in the Northern Hemisphere.  Currently the impact of H2 on tropospheric OH is small, comparable to some of the VOC.

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VOLATILE ORGANIC COMPOUNDS (VOC):  Volatile organic compounds (VOC), which include non-methane hydrocarbons (NMHC) and oxygenated NMHC (e.g., alcohols, aldehydes and organic acids), have short atmospheric lifetimes (fractions of a day to months) and small direct impact on radiative forcing.  VOC influence climate through their production of organic aerosols and their involvement in photochemistry, i.e., production of O3 in the presence of NOx and light.  The largest source, by far, is natural emission from vegetation.  Isoprene, with the largest emission rate, is not stored in plants and is only emitted during photosynthesis.  Monoterpenes are stored in plant reservoirs, so they are emitted throughout the day and night.  The monoterpenes play an important role in aerosol formation.  Vegetation also releases other VOC at relatively small rates, and small amounts of NMHC are emitted naturally by the oceans.  Anthropogenic sources of VOC include fuel production, distribution, and combustion, with the largest source being emissions (i) from motor vehicles due to either evaporation or incomplete combustion of fuel, and (ii) from biomass burning.  Natural emissions occur predominantly in the tropics (23°S to 23°N) with smaller amounts emitted in the northern mid-latitudes and boreal regions mainly in the warmer seasons.  Anthropogenic emissions occur in heavily populated, industrialised regions (95% in the Northern Hemisphere peaking at 40°N to 50°N), where natural emissions are relatively low, so they have significant impacts on regional chemistry despite small global emissions.  A few VOC, such as ethane and acetone, are longer-lived and impact tropospheric chemistry on hemispheric scales.

AEROSOLS:  The production of aerosols represents an important anthropogenic radiative forcing of climate.  Collectively, aerosols block—that is, reflect and absorb—a portion of incoming solar radiation, and this creates a negative radiative forcing.  Aerosols are second only to greenhouse gases in relative importance in their impact on near-surface air temperatures. Unlike the decade-long residence times of the “well-mixed” greenhouse gases, such as CO2 and CH4, aerosols are readily flushed out of the atmosphere within days, either by rain or snow (wet deposition) or by settling out of the air (dry deposition).  Aerosols have the ability to influence climate directly by absorbing or reflecting incoming solar radiation, but they can also produce indirect effects on climate by modifying cloud formation or cloud properties.  Most aerosols serve as condensation nuclei (surfaces upon which water vapour can condense to form clouds); however, darker-coloured aerosols may hinder cloud formation by absorbing sunlight and heating up the surrounding air.  Perhaps the most important type of anthropogenic aerosol in radiative forcing is sulfate aerosol. It is produced from sulfur dioxide (SO2) emissions associated with the burning of coal and oil.  Since the late 1980s, global emissions of SO2 have decreased from about 73 million tons to about 54 million tons of sulfur per year.  Nitrate aerosol is not as important as sulfate aerosol, but it has the potential to become a significant source of negative forcing. One major source of nitrate aerosol is smog (the combination of ozone with oxides of nitrogen in the lower atmosphere) released from the incomplete burning of fuel in internal-combustion engines.  Another source is ammonia (NH3), which is often used in fertilizers or released by the burning of plants and other organic materials. If greater amounts of atmospheric nitrogen are converted to ammonia and agricultural ammonia emissions continue to increase as projected, the influence of nitrate aerosols on radiative forcing is expected to grow.  Both sulfate and nitrate aerosols act primarily by reflecting incoming solar radiation, thereby reducing the amount of sunlight reaching the surface.  Most aerosols, unlike greenhouse gases, impart a cooling rather than warming influence on Earth’s surface.  One prominent exception is carbonaceous aerosols such as carbon black or soot, which are produced by the burning of fossil fuels and biomass.

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Carbon black tends to absorb rather than reflect incident solar radiation, and so it has a warming impact on the lower atmosphere, where it resides. Because of its absorptive properties, carbon black is also capable of having an additional indirect effect on climate. Through its deposition in snowfall, it can decrease the albedo of snow cover. This reduction in the amount of solar radiation reflected back to space by snow surfaces creates a minor positive radiative forcing. Natural forms of aerosol include windblown mineral dust generated in arid and semiarid regions and sea salt produced by the action of waves breaking in the ocean. Changes to wind patterns as a result of climate modification could alter the emissions of these aerosols. In addition, since the concentration of sea salt aerosol, or sea aerosol, increases with the strength of the winds near the ocean surface, changes in wind speed due to global warming and climate change could influence the concentration of sea salt aerosol. For example, some studies suggest that climate change might lead to stronger winds over parts of the North Atlantic Ocean. Areas with stronger winds may experience an increase in the concentration of sea salt aerosol. Other natural sources of aerosols include volcanic eruptions, which produce sulfate aerosol, and biogenic sources (e.g., phytoplankton), which produce dimethyl sulfide (DMS). Other important biogenic aerosols, such as terpenes, are produced naturally by certain kinds of trees or other plants. Anthropogenic pollutants such as nitrate and ozone, both of which serve as precursor molecules for the generation of biogenic aerosol, appear to have increased the rate of production of these aerosols several fold. This process appears to be responsible for some of the increased aerosol pollution in regions undergoing rapid urbanization. Human activity has greatly increased the amount of aerosol in the atmosphere compared with the background levels of preindustrial times. In contrast to the global effects of greenhouse gases, the impact of anthropogenic aerosols is confined primarily to the Northern Hemisphere, where most of the world’s industrial activity occurs. Aerosol emissions may rise in the future, however, as a result of the rapid emergence of coal-fired electric power generation in China and India. The total radiative forcing of all anthropogenic aerosols is approximately –1.2 watts per square metre. Of this total, –0.5 watt per square metre comes from direct effects (such as the reflection of solar energy back into space), and –0.7 watt per square metre comes from indirect effects (such as the influence of aerosols on cloud formation). This negative radiative forcing represents an offset of roughly 40% from the positive radiative forcing caused by human activity. However, the relative uncertainty in aerosol radiative forcing (approximately 90%) is much greater than that of greenhouse gases. It can be said that, if concentrations of anthropogenic aerosols continue to decrease as they have since the 1970s, a significant offset to the effects of greenhouse gases will be reduced, opening future climate to further warming.

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LAND-USE CHANGE:  There are a number of ways in which changes in land use can influence climate. The most direct influence is through the alteration of Earth’s albedo, or surface reflectance.  For example, the replacement of forest by cropland and pasture in the middle latitudes over the past several centuries has led to an increase in albedo, which in turn has led to greater reflection of incoming solar radiation in those regions.  This replacement of forest by agriculture has been associated with a change in global average radiative forcing of approximately –0.2 watt per square metre since 1750.  Land-use changes can also influence climate through their influence on the exchange of heat between Earth’s surface and the atmosphere.  For example, vegetation helps to facilitate the evaporation of water into the atmosphere through evapotranspiration. In this process, plants take up liquid water from the soil through their root systems.  Eventually this water is released through transpiration into the atmosphere, as water vapour through the stomata in leaves.  While deforestation generally leads to surface cooling due to the albedo factor discussed above, the land surface may also be warmed as a result of the release of latent heat by the evapotranspiration process.  The relative importance of these two factors, one exerting a cooling effect and the other a warming effect, varies by both season and region.  While the albedo effect is likely to dominate in middle latitudes, especially during the period from autumn through spring, the evapo-transpiration effect may dominate during the summer in the mid-latitudes and year-round in the tropics. The latter case is particularly important in assessing the potential impacts of continued tropical deforestation.  The rate at which tropical regions are deforested is also relevant to the process of carbon sequestration, the long-term storage of carbon in underground cavities and biomass rather than in the atmosphere.  By removing carbon from the atmosphere, carbon sequestration acts to mitigate global warming.  Deforestation contributes to global warming as fewer plants are available to take up carbon dioxide from the atmosphere.  As fallen trees, shrubs, & other plants are burned or allowed to slowly decompose, they release as carbon dioxide, the carbon they stored during their lifetimes.  Furthermore, any land-use change that influences the amount, distribution, or type of vegetation in a region can affect the concentrations of biogenic aerosols; however, the impact of such changes on climate is indirect and relatively minor. CARBON CYCLE

The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth. It is one of the most important cycles of the earth and allows for carbon to be recycled and reused throughout the biosphere and all of its organisms. The carbon cycle was initially discovered by Joseph Priestley and Antoine Lavoisier, and popularized by Humphry Davy. It is now usually thought of as including the following major reservoirs of carbon interconnected by pathways of exchange:  The Atmosphere  The terrestrial biosphere, which is usually defined to include fresh water systems and non-living organic material, such as soil carbon.  The oceans, including dissolved inorganic carbon and living and non-living marine biota,  The sediments including fossil fuels.

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The Earth's interior, carbon from the Earth's mantle and crust is released to the atmosphere and hydrosphere by volcanoes and geothermal systems. The annual movements of carbon, the carbon exchanges between reservoirs, occur because of various chemical, physical, geological, and biological processes. The ocean contains the largest active pool of carbon near the surface of the Earth, but the deep ocean part of this pool does not rapidly exchange with the atmosphere in the absence of an external influence, such as a black smoker or an uncontrolled deep-water oil well leak. The global carbon budget is the balance of the exchanges (incomes and losses) of carbon between the carbon reservoirs or between one specific loop (e.g., atmosphere ↔ biosphere) of the carbon cycle. An examination of the carbon budget of a pool or reservoir can provide information about whether the pool or reservoir is functioning as a source or sink for carbon dioxide. IN THE ATMOSPHERE

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Carbon exists in the Earth's atmosphere primarily as the gas carbon dioxide (CO2). Although it is a small percentage of the atmosphere (approximately 0.04% on a molar basis), it plays a vital role in supporting life. Other gases containing carbon in the atmosphere are methane and chlorofluorocarbons (the latter is entirely anthropogenic). Trees and other green plants such as grass convert carbon dioxide into carbohydrates during photosynthesis, releasing oxygen in the process. This process is most prolific in relatively new forests where tree growth is still rapid. The effect is strongest in deciduous forests during spring leafing out. This is visible as an annual signal in the Keeling curve of measured CO2 concentration. Northern hemisphere spring predominates, as there is far more land in temperate latitudes in that hemisphere than in the southern. Forests store 86% of the planet's terrestrial above-ground carbon and 73% of the planet's soil carbon. At the surface of the oceans towards the poles, seawater becomes cooler and more carbonic acid is formed as CO2 becomes more soluble. This is coupled to the ocean's thermohaline circulation which transports dense surface water into the ocean's interior. In upper ocean areas of high biological productivity, organisms convert reduced carbon to tissues, or carbonates to hard body parts such as shells and tests. These are, respectively, oxidized (soft-tissue pump) and redissolved (carbonate pump) at lower average levels of the ocean than those at which they formed, resulting in a downward flow of carbon. The weathering of silicate rock (see carbonate-silicate cycle). Carbonic acid reacts with weathered rock to produce bicarbonate ions. The bicarbonate ions produced are carried to the ocean, where they are used to make marine carbonates. Unlike dissolved CO2 in equilibrium or tissues which decay weathering does not move the carbon into a reservoir from which it can readily return to the atmosphere. In 1958, atmospheric carbon dioxide at Mauna Loa was about 320 parts per million (ppm), and in 2013 it was about 391ppm. Future CO2 emission can be calculated by the kaya identity.

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Carbon is released into the atmosphere in several ways:  Through the respiration performed by plants and animals. This is an exothermic reaction and it involves the breaking down of glucose (or other organic molecules) into carbon dioxide and water.  Through the decay of animal and plant matter. Fungi and bacteria break down the carbon compounds in dead animals and plants and convert the carbon to carbon dioxide if oxygen is present, or methane if not.  Through combustion of organic material which oxidizes the carbon it contains, producing carbon dioxide (and other things, like water vapor). Burning fossil fuels such as coal, petroleum products, and natural gas releases carbon that has been stored in the geosphere for millions of years. Burning agrofuels also releases carbon dioxide which has been stored for only a few years or less.  Production of cement. Carbon dioxide is released when limestone (calcium carbonate) is heated to produce lime (calcium oxide), a component of cement.  At the surface of the oceans where the water becomes warmer, dissolved carbon dioxide is released back into the atmosphere. (Course Book by BestCurrentAffairs.com)  Volcanic eruptions and metamorphism release gases into the atmosphere. Volcanic gases are primarily water vapor, carbon dioxide and sulfur dioxide. The carbon dioxide released is roughly equal to the amount removed by silicate weathering; so the two processes, which are the chemical reverse of each other, sum to roughly zero, and do not affect the level of atmospheric carbon dioxide on time scales of less than about 100,000 years.

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IN THE BIOSPHERE

Carbon is an essential part of life on Earth. About half the dry weight of most living organisms is carbon. It plays an important role in the structure, biochemistry, and nutrition of all living cells. Living biomass holds about 575 gigatons of carbon, most of which is wood. Soils hold approximately 1,500 gigatons, mostly in the form of organic carbon, with perhaps a third of that inorganic form of carbon such as calcium carbonate. Autotrophs are organisms that produce their own organic compounds using carbon dioxide from the air or water in which they live. To do this they require an external source of energy. Almost all autotrophs use solar radiation to provide this, and their production process is called photosynthesis. A small number of autotrophs exploit chemical energy sources in a process called chemosynthesis. The most important autotrophs for the carbon cycle are trees in forests on land and phytoplankton in the Earth's oceans. Photosynthesis follows the reaction 6CO2 + 6H2O → C6H12O6 + 6O2 Carbon is transferred within the biosphere as heterotrophs feed on other organisms or their parts (e.g., fruits). This includes the uptake of dead organic material (detritus) by fungi and bacteria for fermentation or decay. Most carbon leaves the biosphere through respiration. When oxygen is present, aerobic respiration occurs, which releases carbon dioxide into the surrounding air or water, following the reaction C6H12O6 + 6O2 → 6CO2 + 6H2O. Otherwise, anaerobic respiration occurs and releases methane into the surrounding environment, which eventually makes its way into the atmosphere or hydrosphere (e.g., as marsh gas or flatulence). Burning of biomass (e.g. forest fires, wood used for heating, anything else organic) can also transfer substantial amounts of carbon to the atmosphere

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Carbon may also be circulated within the biosphere when dead organic matter (such as peat) becomes incorporated in the geosphere. Animal shells of calcium carbonate, in particular, may eventually become limestone through the process of sedimentation.  Much remains to be learned about the cycling of carbon in the deep ocean. For example, a recent discovery is that larvacean mucus houses (commonly known as "sinkers") are created in such large numbers that they can deliver as much carbon to the deep ocean as has been previously detected by sediment traps. Because of their size and composition, these houses are rarely collected in such traps, so most biogeochemical analyses have erroneously ignored them. Carbon storage in the biosphere is influenced by a number of processes on different time-scales: while net primary productivity follows a diurnal and seasonal cycle, carbon can be stored up to several hundreds of years in trees and up to thousands of years in soils. Changes in those long term carbon pools (e.g. through de- or afforestation or through temperaturerelated changes in soil respiration) may thus affect global climate change. IN THE HYDROSPHERE

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The oceans contain around 36,000 gigatonnes of carbon, mostly in the form of bicarbonate ion (over 90%, with most of the remainder being carbonate). Extreme storms such as hurricanes and typhoons bury a lot of carbon, because they wash away so much sediment. For instance, a research team reported that a single typhoon in Taiwan buries as much carbon in the ocean—in the form of sediment—as all the other rains in that country all year long combined.  Inorganic carbon, that is carbon compounds with no carbon-carbon or carbon-hydrogen bonds, is important in its reactions within water. This carbon exchange becomes important in controlling pH in the ocean and can also vary as a source or sink for carbon.  Carbon is readily exchanged between the atmosphere and ocean. In regions of oceanic upwelling, carbon is released to the atmosphere. Conversely, regions of down welling transfer carbon (CO2) from the atmosphere to the ocean.  In the oceans, dissolved carbonate can combine with dissolved calcium to precipitate solid calcium carbonate, CaCO3, mostly as the shells of microscopic organisms. When these organisms die, their shells sink and accumulate on the ocean floor.  Over time these carbonate sediments form limestone which is the largest reservoir of carbon in the carbon cycle.  The dissolved calcium in the oceans comes from the chemical weathering of calcium-silicate rocks, during which carbonic and other acids in groundwater react with calcium-bearing minerals liberating calcium ions to solution and leaving behind a residue of newly formed aluminum-rich clay minerals and insoluble minerals such as quartz.  The flux or absorption of carbon dioxide into the world's oceans is influenced by the presence of widespread viruses within ocean water that infect many species of bacteria. The resulting bacterial deaths spawn a sequence of events that lead to greatly enlarged respiration of carbon dioxide, enhancing the role of the oceans as a carbon sink.

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GLOBAL CARBON PROJECT  The Global Carbon Project (GCP) was established in 2001. The organisation seeks to quantify global carbon emissions and their causes.  The main object of the group has been to fully understand the carbon cycle. The project has brought together emissions experts and economists to tackle the problem of rising concentrations of greenhouse gases.  The Global Carbon Project works collaboratively with the International Geosphere-Biosphere Programme, the World Climate Programme, the International Human Dimensions Programme on Global Environmental Change and Diversitas, under the Earth System Science Partnership.  In late 2006 researchers from the project claimed that carbon dioxide emissions had dramatically increased to a rate of 3.2% annually from 2000.

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CARBON SEQUESTRATION Carbon sequestration is the process through which carbon dioxide (CO2) from the atmosphere is absorbed by trees, plants and crops through photosynthesis, and stored as carbon in biomass (tree trunks, branches, foliage and roots) and soils. The term "sinks" is also used to refer to forests, croplands, and grazing lands, and their ability to sequester carbon. Agriculture and forestry activities can also release CO2 to the atmosphere. Therefore, a carbon sink occurs when carbon sequestration is greater than carbon releases over some time period. Carbon sequestration is the process of capture and long-term storage of atmospheric carbon dioxide (CO2) and may refer specifically to:  "The process of removing carbon from the atmosphere and depositing it in a reservoir." When carried out deliberately, this may also be referred to as carbon dioxide removal, which is a form of geoengineering.  The process of carbon capture and storage, where carbon dioxide is removed from flue gases, such as on power stations, before being stored in underground reservoirs.  Natural biogeochemical cycling of carbon between the atmosphere and reservoirs, such as by chemical weathering of rocks.  Carbon sequestration describes long-term storage of carbon dioxide or other forms of carbon to either mitigate or defer global warming and avoid dangerous climate change. It has been proposed as a way to slow the atmospheric and marine accumulation of greenhouse gases, which are released by burning fossil fuels.  Carbon dioxide is naturally captured from the atmosphere through biological, chemical or physical processes. Some anthropogenic sequestration techniques exploit these natural processes, while some use entirely artificial processes.  Carbon dioxide may be captured as a pure by-product in processes related to petroleum refining or from flue gases from power generation. CO2 sequestration includes the storage part of carbon capture and storage, which refers to large-scale, permanent artificial capture and sequestration of industrially produced CO2 using subsurface saline aquifers, reservoirs, ocean water, aging oil fields, or other carbon sinks. Biological processes: Biosequestration or carbon sequestration through biological processes affects the global carbon cycle. Examples include major climatic fluctuations, such as the Azolla event, which created the current Arctic climate. Such processes created fossil fuels, as well as clathrate or limestone. By manipulating such processes, geoengineers seek to enhance sequestration.  Peat production: Peat bogs are a very important carbon store. By creating new bogs, or enhancing existing ones, carbon can be sequestered.  Reforestation: Reforestation is the replanting of trees on marginal crop and pasture lands to incorporate carbon from atmospheric CO2 into biomass. For this process to succeed the carbon must not return to the atmosphere from burning or

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rotting when the trees die. To this end, the trees must grow in perpetuity or the wood from them must itself be sequestered, e.g., via biochar, bio-energy with carbon storage (BECS) or landfill. Short of growth in perpetuity, however, reforestation with long-lived trees (>100 years) will sequester carbon for a more graduated release, minimizing impact during the "carbon crisis" of the 21st century. Agriculture: Globally, soils are estimated to contain approximately 1,500 gigatons of organic carbon, more than the amount in vegetation and the atmosphere.  Modification of agricultural practices is a recognized method of carbon sequestration as soil can act as an effective carbon sink offsetting as much as 20% of 2010 carbon dioxide emissions annually.  Carbon emission reduction methods in agriculture can be grouped into two categories: reducing and/or displacing emissions and enhancing carbon removal. Some of these reductions involve increasing the efficiency of farm operations (i.e. more fuel-efficient equipment) while some involve interruptions in the natural carbon cycle. Also, some effective techniques (such as the elimination of stubble burning) can negatively impact other environmental concerns (increased herbicide use to control weeds not destroyed by burning). Reducing emissions: Increasing yields and efficiency generally reduces emissions as well, since more food results from the same or less effort. Techniques include more accurate use of fertilizers, less soil disturbance, better irrigation, and crop strains bred for locally beneficial traits and increased yields.  Replacing more energy intensive farming operations can also reduce emissions. Reduced or no-till farming requires less machine use and burns correspondingly less fuel per acre. However, no-till usually increases use of weed-control chemicals and the residue now left on the soil surface is more likely to release its CO2 to the atmosphere as it decays, reducing the net carbon reduction.  In practice, most farming operations that incorporate post-harvest crop residues, wastes and byproducts back into the soil provide a carbon storage benefit. This is particularly the case for practices such as field burning of stubble - rather than releasing almost all of the stored CO2 to the atmosphere, tillage incorporates the biomass back into the soil where it can be absorbed and a portion of it stored permanently. Enhancing carbon removal: All crops absorb CO2 during growth and release it after harvest. The goal of agricultural carbon removal is to use the crop and its relation to the carbon cycle to permanently sequester carbon within the soil. This is done by selecting farming methods that return biomass to the soil and enhance the conditions in which the carbon within the plants will be reduced to its elemental nature and stored in a stable state. Methods for accomplishing this include: Use cover crops such as grasses and weeds as temporary cover between planting seasons Concentrate livestock in small paddocks for days at a time so they graze lightly but evenly. This encourages roots to grow deeper into the soil. Stock also till the soil with their hooves, grinding old grass and manures into the soil. Cover bare paddocks with hay or dead vegetation. This protects soil from the sun and allows the soil to hold more water and be more attractive to carbon-capturing microbes. Restore degraded land, which slows carbon release while returning the land to agriculture or other use. Agricultural sequestration practices may have positive effects on soil, air, and water quality, be beneficial to wildlife, and expand food production. On degraded croplands, an increase of 1 ton of soil carbon pool may increase crop yield by 20 to 40 kilograms per hectare of wheat, 10 to 20 kg/ ha for maize, and 0.5 to 1 kg/ha for cowpeas. The effects of soil sequestration can be reversed. If the soil is disrupted or tillage practices are abandoned, the soil becomes a net source of greenhouse gases. Typically after 15 to 30 years of sequestration, soil becomes saturated and ceases to absorb carbon. This implies that there is a global limit to the amount of carbon that soil can hold. Many factors affect the costs of carbon sequestration including soil quality, transaction costs and various externalities such as leakage and unforeseen environmental damage. Because reduction of atmosperic CO2 is a long-term concern, farmers can be reluctant to adopt more expensive agricultural techniques when there is not a clear crop, soil, or economic benefit. Governments such as Australia and New Zealand are considering allowing farmers to sell carbon credits once they document that they have sufficiently increased soil carbon content. Key Agricultural Typical definition and some examples Effect on greenhouse gases Practices Conservation or Grasses or trees planted along streams and Increases carbon storage through riparian buffers croplands to prevent soil erosion and nutrient sequestration. runoff into waterways. Conservation tillage on Typically defined as any tillage and planting Increases carbon storage through croplands system in which 30% or more of the crop residue enhanced soil sequestration, may remains on the soil after planting. This disturbs the reduce energy-related CO2 soil less, and therefore allows soil carbon to emissions from farm equipment, accumulate. There are different kinds of and could affect N2O positively or conservation tillage systems, including no till, ridge negatively. till, minimum till and mulch till. Grazing land Modification to grazing practices that produce beef Increases carbon storage through management and dairy products that lead to net greenhouse enhanced soil sequestration and gas reductions (e.g., rotational grazing). may affect emissions of CH4 and N2O. Biofuel substitution Displacement of fossil fuels with biomass (e.g., Substitutes carbon for fossil fuel and agricultural and forestry wastes, or crops and energy-intensive products. Burning trees grown for biomass purposes) in energy and growing of biomass can also production, or in the production of energyaffect soil N2O emissions. intensive products like steel.

RADIATIVE FORCING  The temperature of Earth’s surface and lower atmosphere may be modified in three ways: (1) Through a net increase in the solar radiation entering at the top of Earth’s atmosphere, (2) Through a change in the fraction of the radiation reaching the surface, and (3) Through a change in the concentration of greenhouse gases in the atmosphere.  In each case the changes can be thought of in terms of “radiative forcing.”

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As defined by the Intergovernmental Panel on Climate Change (IPCC), radiative forcing is a measure of the influence a given climatic factor has on the amount of downward-directed radiant energy impinging upon Earth’s surface. Climatic factors are divided between those caused primarily by human activity (such as greenhouse gas emissions and aerosol emissions) and those caused by natural forces (such as solar irradiance); then, for each factor, so-called forcing values are calculated for the time period between 1750 and the present day. “Positive forcing” is exerted by climatic factors that contribute to the warming of Earth’s surface, whereas “negative forcing” is exerted by factors that cool Earth’s surface. On average about 342 watts of solar radiation strike each square metre of Earth’s surface per year, and this quantity can in turn be related to a rise or fall in Earth’s surface temperature. Temperatures at the surface may also rise or fall through a change in the distribution of terrestrial radiation (that is, radiation emitted by Earth) within the atmosphere. In some cases, radiative forcing has a natural origin, such as during explosive eruptions from volcanoes where vented gases and ash block some portion of solar radiation from the surface. In other cases, radiative forcing has an anthropogenic, or exclusively human, origin. For example, anthropogenic increases in carbon dioxide, methane, and nitrous oxide are estimated to account for 2.3 watts per square metre of positive radiative forcing. When all values of positive and negative radiative forcing are taken together and all interactions between climatic factors are accounted for, the total net increase in surface radiation due to human activities since the beginning of the Industrial Revolution is 1.6 watts per square metre.

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CLIMATE CHANGE INDICATORS  Temperature rise: The IPCC predicts a rise in annual mean surface temperatures of between 1.4 and 5.8ºC over the period 1990 to 2100. A mid-range temperature rise scenario will have a devastating effect on food security not only in the tropical and sub-tropical regions of the world but also in the mid-latitudes. Temperature rises of just 2-3 degrees will see crop yields in Africa, the Middle East and South Asia fall by as much as 30 to 40%. Higher average temperatures will also stimulate the emergence and re-emergence of pests and diseases, and increase the vectors that carry disease.  Ice melt: 1.7 billion people currently live in water-stressed countries but this number is expected to increase to 5 billion by 2025. Retreating glaciers and snowlines will increase variability in river flow, diminish consistent water supplies and exacerbate these stresses. The South Asian sub-continent and South America are both likely to suffer. Sea level rise is predicted to be between 0.09 and 0.88 metres over the period 1990 to 2100. Higher sea levels will have catastrophic implications for small Pacific states and low-lying countries such as Bangladesh, and also for all major coastal cities.  Extreme weather events: Increased precipitation will lead to more extensive flooding. These impacts will be accentuated in areas where drought has hardened the earth and increased the likelihood of flash floods. Flooding leads to soil erosion and results in landslides which cause extensive damage to dwellings and livelihoods. The Asian monsoon is sensitive to small temperature changes and stands to wreak havoc across the sub-continent. In July 2005, Mumbai received 37 inches of rain in 24 hours, the largest downpour recorded in an Indian city. Increased incidence of heat waves will result in illness and death, especially amongst the old and very young. Increased storm surges will have a significant impact on coastal settlements.  Length of growing season: The length of a growing season depends on the first and last day of a base temperature above which plants will grow. Increased climate variability is currently leading to unpredictable changes in the length of the growing seasons for all sorts of crops all around the world. This is the major concern not only for farmers whose livelihoods depend on consistent crop yields, but also to the billions of people living in poverty who are dramatically affected by variability in food prices. Climate variability can also play havoc with the natural breeding cycle of insects and animals, and the balance of the ecosystems that they live within.  Acidification of the oceans: The oceans absorb carbon dioxide from the atmosphere, form carbonic acid and reduce the pH of the water. The oceans have already absorbed 50% of the carbon dioxide that we have produced since the industrial revolution. The lowering of the ocean’s pH has a significant impact on the ability of small marine organisms to form shells. These organisms play a crucial role at the bottom of the marine food chain. Acidification also damages coral. Impacts on marine biodiversity and the coral reefs have significant implications for the communities who are dependent on already depleted fisheries for their subsistence and livelihood.  Human security: Indirect impacts have further implications for developing countries. The effects of climate change and the resultant reduction in the environment’s ‘carrying capacity’ in terms of food, water and energy quickly lead to security issues. It is easy to see that when food and water security are compromised, the likelihood of conflict and social insecurity increases.  Energy Security: Energy security is also threatened by extreme weather events that undermine the stability of ports and drilling rigs. Glacier retreat and ice cap melt will impact on hydro-electricity and melting permafrost will weaken pipelines. Energy insecurity jeopardizes the social and economic services that improve people’s capabilities and ameliorate the affects of poverty. The cumulative effect of all these factors will be to undermine the very basis of governance and productivity. With less capital and more desperate circumstances, the fabric of civilization itself becomes threatened. Consequently, action and support from developed countries on climate change has to be seen in the context of an overall responsibility to promote sustainable development and to fight poverty as expressed in the Millennium Development Goals. GLOBAL DIMMING  Global dimming is gradual decrease of the sun's radiation quantity that comes to Earth's surface, and is the result of tiny particles' increased quantity that had come to atmosphere by human activities (combustion of different fuels).  Independent researches in Israel and Holland showed that amount of the radiation which reach to the surface have decrease by average of 2-3% each decade, and in certain areas even bigger decrease.  When scientists started global dimming phenomenon researches they weren't able to find any cause responsible for such drastically decrease in sun's radiation that reaches earth's surface.  Especially since quantity of particles that went into the atmosphere as the result of fossil fuels combustion wasn’t sufficient for such large consequences. Their further researches showed that these particles aren't blocking sun radiation on level required to cause global dimming.  Global dimming is result of interaction of these particles with clouds and water that reside in atmosphere, and that combination acts like big mirror for Sun’s radiation, mirroring the Sun’s radiation back to universe.

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To understand why these additional particles increase reflectivity of clouds first we must know the conditions required for creation of rain. To put it simply, in normal conditions clouds are made of water steam and tiny particles called aerosols that are invisible to human eye. When these conditions become adequate small particles of water are starting to gather on these particles and once they're big enough rain starts to fall. The problem that actually causes the global dimming is increased quantity of aerosols in the atmosphere since small water particles have then much more particles on which they can gather and this results in much more tiny particles in the cloud than it's natural in normal conditions. These drops of water are now reflecting sun radiation back to space with much more efficiency because there is same quantity of water now spread in more of these particles. Rich countries have many different laws and regulations that have purpose in limiting the emission of particles when burning fuels and because of this global dimming effect started its decrease in Europe and America and somewhere about 1990 there was increase in quantity of sun radiation that gets to surface. The problem concerning global dimming lies in developing countries like China and India that are now having the same process as it was in Europe and North America in 70s and 80s, when there was big industrialization with no real efforts to protect the environment. This past global dimming didn't seriously affect Europe and North America, but it did strike the poorest countries in Africa. Because of the decreased ocean vaporization, monsoon rain zone that has season movement from south to north and back, didn't came in these years north enough and caused the hunger in Sub-Saharan Africa. This part of the world is specific since rain falls only once in one year, in monsoon season and disappearance of these monsoon rains destroyed crops and the cattle hadn't survived either. Once western countries, because of the new regulations started decreasing amount of released particles into the atmosphere, monsoon rains returned to their normal condition that was before this crisis.

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Relation between Global warming and global dimming:  Researches pointed the conclusion that global dimming in fact moderates global warming effect and that global warming and global dimming are two opposite effects and current state favors global warming because of increase in average temperatures on Earth.  Logical conclusion from this would be that if we could increase emissions of tiny particles into the atmosphere we could solve the global warming problem without reducing the greenhouse gases emission.  This is in fact true, but side effects of the tiny articles emission are acid rains and health problem. But not only that, this also wouldn’t be ethical since this would be once again causing the problem of monsoon rains in Africa causing another hunger in Sub-Saharan Africa.  If we assume that in about 20 year time developing countries will accept standards for preservation of air quality like western countries, this would be ideal conditions for acceleration of global warming.  The problem lies in the fact that western countries have not limited greenhouse gases emissions; they only limited emission of tiny particles into atmosphere.  Result of those measures is decreased global dimming effect, but global warming effect is still increasing because of greenhouse gases. And if this example is followed by developing countries then global dimming effect will be returning to levels before industrialization, but in the same time global warming effect will be increased because of the greenhouse gases emissions.  To put it in other words, current effect of global dimming that moderate the intensity of global warming will be lost.

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SINKS OF GHGs Sinks refer to 'storehouses' of the gases - places where they can be sequestered.  The oceans are, perhaps, the biggest sink and contain about 40000 GtC (giga tonnes of carbon). By contrast, the atmosphere contains 750 Gt and the terrestrial biosphere, 2200 Gt.  Vegetation and soil also have the capacity to sequester carbon. Soils also remove methane to some degree.  Atmospheric methane, however, is removed mainly by its oxidation by the OH radical in the troposphere.  Halocarbons do not have any significant mechanism of removal. They persist in the upper atmosphere (mid-upper stratosphere) for long periods and break down in the presence of sunlight. Nitrous oxide may also break down in this manner.

VULNERABILITY AND ADAPTATION Severe storms, floods and droughts since the eighties have served as reminders that climate change is a global problem. The most dramatic change has been in the temperature, with measurement records suggesting that warming by 0.3-0.6 th °C has already taken place since the 1860s. The last two decades of the 20 century were the warmest in this period. Over the next hundred years, the earth's surface temperature is projected to increase by 1.4 to 5.8 °C which will be greater than that experienced over the last 10000 years. Climate changes have occurred in the past, but always gradually, over thousands of years, giving ecosystems time to adapt. The rapid change that is currently taking place will leave ecosystems vulnerable. The large quantities of water locked in the polar ice caps and glaciers will be released as a consequence of warming. This, together with an increase in the thermal expansion of the oceans, will make the global mean sea level rise by 9 cm to 88 cm. The effects of global warming are difficult to quantify because of the complicated relationships between air temperature, precipitation quantity and pattern, vegetative cover and soil moisture. However, it is likely that the frequency, intensity and duration of storms and other extreme weather events could increase. POTENTIAL EFFECTS OF GLOBAL WARMING  The path of future climate change will depend on what courses of action are taken by society—in particular the emission of greenhouse gases from the burning of fossil fuels.  A range of alternative emissions scenarios have been proposed by the IPCC to predict future climate changes. These scenarios depend on various assumptions concerning future rates of human population growth, economic development, energy demand, technological advancement, and other factors.  Scenarios with the smallest increases in greenhouse gases are associated with low-to-moderate economic growth and increasing use of more environmentally friendly and resource-efficient technologies or with rapid economic growth and use of alternative energy sources.

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In each of these scenarios, CO2 concentrations at the year 2100 are held near or below twice the levels of the preindustrial age—that is, at or below 600 ppm. At the other extreme are scenarios that assume either more intensive use of fossil fuels or unabated growth in world population. In these scenarios CO2 concentrations approach or exceed 900 ppm by 2100. The intermediate scenarios reflect so-called “business-as-usual” (BAU) activities, where civilization continues to burn fossil fuels at early 21st-century rates. In the BAU scenarios CO2 concentrations approach levels of 700–750 ppm by 2100.

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Projected range of sea-level rise by climate change scenario Scenario Temperature change (°C) Sea-level rise (m) in 2090–99 relative to 1980–99 in 2090–99 relative to 1980–99 B1 1.1–2.9 0.18–0.38 A1T 1.4–3.8 0.20–0.45 B2 1.4–3.8 0.20–0.43 A1B 1.7–4.4 0.21–0.48 A2 2.0–5.4 0.23–0.51 A1Fl 2.4–6.4 0.26–0.59

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Simulations of future climate change  The differences between the various simulations arise from disparities between the various climate models used and from assumptions made by each emission scenario.  For example, best estimates of the predicted increases in global surface temperature between the years 2000 and 2100 range from about 1.8 °C (3.2 °F) to about 4 °C (7.2 °F), depending on which emission scenario is assumed and which climate model is used.  These projections are conservative in that they do not take into account potential positive carbon cycle feedbacks.  Only the lower-end emissions scenarios are likely to hold additional global surface warming by 2100 to less than 2 °C (3.6 °F)—a level considered by many scientists to be the threshold above which pervasive and extreme climatic effects will occur.

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Patterns of warming  The greatest increase in near-surface air temperature is projected to occur over the polar region of the Northern Hemisphere because of the melting of sea ice and the associated reduction in surface albedo.  Greater warming is predicted over land areas than over the ocean. Largely due to the delayed warming of the oceans and their greater specific heat, the Northern Hemisphere—with less than 40 percent of its surface area covered by water—is expected to warm faster than the Southern Hemisphere.  Some of the regional variation in predicted warming is expected to arise from changes to wind patterns and ocean currents in response to surface warming.  For example, the warming of the region of the North Atlantic Ocean just south of Greenland is expected to be slight. This anomaly is projected to arise from a weakening of warm northward ocean currents combined with a shift in the jet stream that will bring colder polar air masses to the region.

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Precipitation patterns  The climate changes associated with global warming are also projected to lead to changes in precipitation patterns across the globe.  Increased precipitation is predicted in the polar and subpolar regions, whereas decreased precipitation is projected for the middle latitudes of both hemispheres as a result of the expected poleward shift in the jet streams.  Whereas precipitation near the Equator is predicted to increase, it is thought that rainfall in the subtropics will decrease. Both phenomena are associated with a forecasted strengthening of the tropical Hadley cell pattern of atmospheric circulation.  Changes in precipitation patterns are expected to increase the chances of both drought and flood conditions in many areas.  Decreased summer precipitation in North America, Europe, and Africa, combined with greater rates of evaporation due to warming surface temperatures, is projected to lead to decreased soil moisture and drought in many regions.  Furthermore, since anthropogenic climate change will likely lead to a more vigorous hydrologic cycle with greater rates of both evaporation and precipitation, there will be a greater probability for intense precipitation and flooding in many regions.

Regional predictions  Regional predictions of future climate change remain limited by uncertainties in how the precise patterns of atmospheric winds and ocean currents will vary with increased surface warming.  For example, some uncertainty remains in how the frequency and magnitude of El Nino/Southern Oscillation (ENSO) events will adjust to climate change.  Since ENSO is one of the most prominent sources of inter-annual variations in regional patterns of precipitation and temperature, any uncertainty in how it will change implies a corresponding uncertainty in certain regional patterns of climate change.  For example, increased El Nino activity would likely lead to more winter precipitation in some regions, such as the desert southwest of the United States.  This might offset the drought predicted for those regions, but at the same time it might lead to less precipitation in other regions.  Rising winter precipitation in the desert southwest of the United States might exacerbate drought conditions in locations as far away as South Africa. Ice melt and sea-level rise  A warming climate holds important implications for other aspects of the global environment. Because of the slow process of heat diffusion in water, the world’s oceans are likely to continue to warm for several centuries in response to increases in greenhouse concentrations that have taken place so far.

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The combination of seawater’s thermal expansion associated with this warming and the melting of mountain glaciers is predicted to lead to an increase in global sea level of 0.21–0.48 metre (0.7–1.6 feet) by 2100 under the BAU emissions scenario. However, the actual rise in sea level could be considerably greater than this. It is probable that the continued warming of Greenland will cause its ice sheet to melt at accelerated rates. In addition, this level of surface warming may also melt the ice sheet of West Antarctica. Paleoclimatic evidence suggests that an additional 2 °C (3.6 °F) of warming could lead to the ultimate destruction of the Greenland Ice Sheet, an event that would add another 5 to 6 metres (16 to 20 feet) to predicted sea-level rise. Such an increase would submerge a substantial number of islands and lowland regions. Selected lowland regions include substantial parts of the U.S. Gulf Coast and Eastern Seaboard (including roughly the lower third of Florida), much of the Netherlands and Belgium (two of the European Low Countries), and heavily populated tropical areas such as Bangladesh. In addition, many of the world’s major cities—such as Tokyo, New York, Mumbai (Bombay), Shanghai, and Dhaka—are located in lowland regions vulnerable to rising sea levels. With the loss of the West Antarctic ice sheet, additional sea-level rise would approach 10.5 metres (34 feet). While the current generation of models predicts that such global sea-level changes might take several centuries to occur, it is possible that the rate could accelerate as a result of processes that tend to hasten the collapse of ice sheets. One such process is the development of moulins, or large, vertical shafts in the ice that allow surface meltwater to penetrate to the base of the ice sheet. A second process involves the vast ice shelves off Antarctica that buttress the grounded continental ice sheet of Antarctica’s interior. If these ice shelves collapse, the continental ice sheet could become unstable, slide rapidly toward the ocean, and melt, thereby further increasing mean sea level. Thus far, neither process has been incorporated into the theoretical models used to predict sea-level rise.

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Ocean circulation changes  Another possible consequence of global warming is a decrease in the global ocean circulation system known as the “thermohaline circulation” or “great ocean conveyor belt.”  This system involves the sinking of cold saline waters in the subpolar regions of the oceans, an action that helps to drive warmer surface waters poleward from the subtropics.  As a result of this process, a warming influence is carried to Iceland and the coastal regions of Europe that moderates the climate in those regions.  Some scientists believe that global warming could shut down this ocean current system by creating an influx of fresh water from melting ice sheets and glaciers into the subpolar North Atlantic Ocean.  Since fresh water is less dense than saline water, a significant intrusion of fresh water would lower the density of the surface waters and thus inhibit the sinking motion that drives the large-scale thermohaline circulation.  It has also been speculated that, as a consequence of large-scale surface warming, such changes could even trigger colder conditions in regions surrounding the North Atlantic.  Experiments with modern climate models suggest that such an event would be unlikely. Instead, a moderate weakening of the thermohaline circulation might occur that would lead to a dampening of surface warming—rather than actual cooling—in the higher latitudes of the North Atlantic Ocean. We Revise and Update our Books Every Year according the changing Trend of the Exam.

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Tropical cyclones  One of the more controversial topics in the science of climate change involves the impact of global warming on tropical cyclone activity. It appears likely that rising tropical ocean temperatures associated with global warming will lead to an increase in the intensity (and the associated destructive potential) of tropical cyclones.  In the Atlantic a close relationship has been observed between rising ocean temperatures and a rise in the strength of hurricanes.  Trends in the intensities of tropical cyclones in other regions, such as in the tropical Pacific and Indian oceans, are more uncertain due to a paucity of reliable long-term measurements.  The warming of oceans favours increased tropical cyclone intensities.

Environmental consequences of global warming  Global warming and climate change have the potential to alter biological systems.  More specifically, changes to near-surface air temperatures will likely influence ecosystem functioning and thus the biodiversity of plants, animals, and other forms of life.  The current geographic ranges of plant and animal species have been established by adaptation to long-term seasonal climate patterns.  As global warming alters these patterns on timescales considerably shorter than those that arose in the past from natural climate variability, relatively sudden climatic changes may challenge the natural adaptive capacity of many species.  It has been estimated that one-fifth to one-third of all plant and animal species are likely to be at an increased risk of extinction if global average surface temperatures rise another 1.5 to 2.5 °C (2.7 to 4.5 °F) by the year 2100.  A 40% extinction rate would likely lead to major changes in the food webs within ecosystems and has a destructive impact on ecosystem function.  Surface warming in temperate regions is likely to lead changes in various seasonal processes—for instance, earlier leaf production by trees, earlier greening of vegetation, altered timing of egg-laying and hatching, and shifts in the seasonal migration patterns of birds, fishes, and other migratory animals.  In high-latitude ecosystems, changes in the seasonal patterns of sea ice threaten predators such as polar bears and walruses. (Both species rely on broken sea ice for their hunting activities.)  Also in the high latitudes, a combination of warming waters, decreased sea ice, and changes in ocean salinity and circulation is likely to lead to reductions or redistributions in populations of algae and plankton. As a result, fish and other organisms that forage upon algae and plankton may be threatened.  On land, rising temperatures and changes in precipitation patterns and drought frequencies are likely to alter patterns of disturbance by fires and pests.

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Other likely impacts on the environment include the destruction of many coastal wetlands, salt marshes, and mangrove swamps as a result of rising sea levels and the loss of certain rare and fragile habitats that are often home to specialist species that are unable to thrive in other environments. For example, certain amphibians limited to isolated tropical cloud forests either have become extinct already or are under serious threat of extinction. Cloud forests—tropical forests that depend on persistent condensation of moisture in the air—are disappearing as optimal condensation levels move to higher elevations in response to warming temperatures in the lower atmosphere. In many cases a combination of stresses caused by climate change as well as human activity represents a considerably greater threat than either climatic stresses or non-climatic stresses alone. A particularly important example is coral reefs, which contain much of the ocean’s biodiversity. Rising ocean temperatures increase the tendency for coral bleaching (a condition where zooxanthellae, or yellow-green algae, living in symbiosis with coral either lose their pigments or abandon the coral polyps altogether), and they also raise the likelihood of greater physical damage by progressively more destructive tropical cyclones. In many areas coral is also under stress from increased ocean acidification, marine pollution, runoff from agricultural fertilizer, and physical damage by boat anchors and dredging. Climate and non-climatic stresses are threat to migratory animals. As these animals attempt to relocate to regions with more favorable climate conditions, they are likely to encounter impediments such as highways, walls, artificial waterways, and other man-made structures. Warmer temperatures are also likely to affect the spread of infectious diseases, since the geographic ranges of carriers, such as insects and rodents, are often limited by climatic conditions. Warmer winter conditions in New York in 1999, for example, appear to have facilitated an outbreak of West Nile virus, whereas the lack of killing frosts in New Orleans during the early 1990s led to an explosion of disease-carrying mosquitoes and cockroaches. Warmer winters in the Korean peninsula and southern Europe have allowed the spread of the Anopheles mosquito, which carries the malaria parasite, whereas warmer conditions in Scandinavia in recent years have allowed for the northward advance of encephalitis. In the southwestern United States, alternations between drought and flooding related in part to the ENSO phenomenon have created conditions favorable for the spread of hanta viruses by rodents. The spread of mosquito-borne Rift Valley fever in equatorial East Africa has also been related to wet conditions in the region associated with ENSO. Severe weather conditions conducive to rodents or insects have been implicated in infectious disease outbreaks—for instance, the outbreaks of cholera and leptospirosis that occurred after Hurricane Mitch struck Central America in 1998. Global warming could therefore affect the spread of infectious disease through its influence on ENSO or on severe weather conditions. SOCIO-ECONOMIC CONSEQUENCES OF GLOBAL WARMING

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Socio-economic impacts of global warming could be substantial depending on the actual temperature increases over the next century.  Models predict that a net global warming of 1 to 3 °C (1.8 to 5.4 °F) beyond the late-20th-century global average would produce economic losses in some regions (particularly the tropics and high latitudes) and economic benefits in others.  For warming beyond these levels, benefits would tend to decline and costs increase. For warming in excess of 4 °C (7.2 °F), models predict that costs will exceed benefits on average, with global mean economic losses estimated between 1 and 5 percent of gross domestic product.  Substantial disruptions could be expected under these conditions, specifically in the areas of agriculture, food and forest products, water and energy supply, and human health.  Agricultural productivity might increase modestly in temperate regions for some crops in response to a local warming of 1–3 °C (1.8–5.4 °F), but productivity will generally decrease with further warming.  For tropical and subtropical regions, models predict decreases in crop productivity for even small increases in local warming.  In some cases, adaptations such as altered planting practices are projected to ameliorate losses in productivity for modest amounts of warming.  An increased incidence of drought and flood events would likely lead to further decreases in agricultural productivity and to decreases in livestock production, particularly among subsistence farmers in tropical regions.  In regions such as the African Sahel, decreases in agricultural productivity have already been observed as a result of shortened growing seasons, which in turn have occurred as a result of warmer and drier climatic conditions.  In other regions, changes in agricultural practice, such as planting crops earlier in the growing season, have been undertaken.  The warming of oceans is predicted to have an adverse impact on commercial fisheries by changing the distribution and productivity of various fish species, whereas commercial timber productivity may increase globally with modest warming.  Water resources are likely to be affected substantially by global warming. At current rates of warming, a 10–40 percent increase in average surface runoff and water availability has been projected in higher latitudes and in certain wet regions in the tropics by the middle of the 21st century, while decreases of similar magnitude are expected in other parts of the tropics and in the dry regions in the subtropics. This would be particularly severe during the summer season.  In many cases water availability is already decreasing or expected to decrease in regions that have been stressed for water resources since the turn of the 21st century.  Such regions as the African Sahel, western North America, southern Africa, the Middle East, and Western Australia continue to be particularly vulnerable. In these regions drought is projected to increase in both magnitude and extent, which would bring about adverse effects on agriculture and livestock raising.  Earlier and increased spring runoff is already being observed in western North America and other temperate regions served by glacial or snow-fed streams and rivers. Fresh water currently stored by mountain glaciers and snow in both the tropics and extra-tropics is also projected to decline and thus reduce the availability of fresh water for more than 15 percent of the world’s population.  It is also likely that warming temperatures, through their impact on biological activity in lakes and rivers, may have an adverse impact on water quality, further diminishing access to safe water sources for drinking or farming. For example, warmer waters favour an increased frequency of nuisance algal blooms, which can pose health risks to humans.

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HEALTH CONCERN Temperature related morbidity: Vector borne diseases

Health effects extreme weather

Health effects due to insecurity

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VULNERABILITIES DUE TO CLIMATE CHANGE Heat and cold related illness Cardio vascular illnesses Changed patterns of diseases by region and by climate parameter Malaria, Filaria, Kala-azar, Japanese Encephalitis, and Dengue caused by bacteria, viruses and other pathogens carried by mosquitoes, ticks, and other vectors. Diarrhea, Cholera and intoxication caused by biological and chemical contaminants in water Damaged public health infrastructure due to cyclones / floods Injuries and illness Social and mental health stress due to disasters and displacement Malnutrition, hunger, particularly in children

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Energy availability and use could be affected in at least two distinct ways by rising surface temperatures. In general, warmer conditions would favour an increased demand for air-conditioning; however, this would be at least partially offset by decreased demand for winter heating in temperate regions. Energy generation that requires water either directly, as in hydroelectric power, or indirectly, as in steam turbines used in coalfired power plants or in cooling towers used in nuclear power plants, may become more difficult in regions with reduced water supplies. As discussed above, it is expected that human health will be further stressed under global warming conditions by potential increases in the spread of infectious diseases. Declines in overall human health might occur with increases in the levels of malnutrition due to disruptions in food production and by increases in the incidence of afflictions. Such afflictions could include diarrhea, cardio respiratory illness, and allergic reactions in the mid-latitudes of the Northern Hemisphere as a result of rising levels of pollen. Rising heat-related mortality, such as that observed in response to the 2003 European heat wave, might occur in many regions, especially in impoverished areas where air-conditioning is not generally available. The economic infrastructure of most countries is predicted to be severely strained by global warming and climate change. Poor countries and communities with limited adaptive capacities are likely to be disproportionately affected. Projected increases in the incidence of severe weather, heavy flooding, and wildfires associated with reduced summer ground moisture in many regions will threaten homes, dams, transportation networks and other facets of human infrastructure. In high-latitude and mountain regions, melting permafrost is likely to lead to ground instability or rock avalanches, further threatening structures in those regions. Rising sea levels and the increased potential for severe tropical cyclones represent a heightened threat to coastal communities throughout the world. It has been estimated that an additional warming of 1–3 °C (1.8–5.4 °F) beyond the late-20th-century global average would threaten millions more people with the risk of annual flooding. People in the densely populated, poor, low-lying regions of Africa, Asia, and tropical islands would be the most vulnerable, given their limited adaptive capacity. In addition, certain regions in developed countries, such as the Low Countries of Europe and the Eastern Seaboard and Gulf Coast of the United States, would also be vulnerable to the effects of rising sea levels. Adaptive steps are already being taken by some governments to reduce the threat of increased coastal vulnerability through the construction of dams and drainage works.

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IMPACT OF CLIMATE CHANGE ON INDIA

CLIMATE CHANGE IN HIMALAYAN REGION  The Himalayan region, one of the most dynamic and complex mountain ranges, has a profound effect on the climate of the Indian subcontinent. It prevents frigid, dry Arctic winds from blowing south into the subcontinent, which keeps South Asia much warmer than corresponding temperate regions in the other continents. It also forms a barrier for the monsoon winds, keeping them from travelling northwards, and causing heavy rainfall in the Terai region. :: But now Himalayas are vulnerable to global climate change and increasing human activities. In addition to the already existing threats and pressures on mountain ecosystem, climate change can be an additional burden to bear by the mountain ecosystems, species and peoples.  The Himalayan glaciers are the second largest body of ice in the world, covering 17% (3 million hectares) of the mountain area and are the source of water for the numerous rivers that flow across the Indo-Gangetic plains. :: Unfortunately, the Himalayan glaciers are retreating faster than any other glaciers. The image shows the approximate recession of the Gangotri glacier- one of the largest glaciers in the Himalayans. From 1780 to 2001 this glacier retreated almost 2 km.  Millions of the peoples living in Himalayan region are relying on the glacial melt waters from the Himalayan glaciers. A decline in glacier mass balance can mean less water available for rivers.  It is a worry that the receding glacier trend could lead to the Ganga, Indus, Brahmaputra and other rivers in northern India becoming seasonal rivers (IPCC 2007). If these major rivers are dry during the summer months. It will affect the water supply for irrigation. IMPACT ON FORESTS  An assessment of the impact of climate change projections on forest ecosystems for the two greenhouse gas emission scenarios for 2085 showed that 68% and 77% of forested grid are likely to experience shifts in forest vegetation type.  Notably, the country’s dominant forest cover, characterized by Moist Savanna (32.5%) and Dry Savanna (33%) is projected to change, such that Tropical Dry Forest (37.2%) and Tropical Seasonal Forest (28.4%) become dominant.

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IMPACTS ON WATER AND AGRICULTURE  The presence of highly complex river basin systems indicates the importance of glaciated mountains, which account for most of the glacial melt water. Both glacial melt water and monsoonal precipitation provide a significant component of water resources for different parts of the country. While snow and glacier melt are the major factors in the western and central Himalayan region, rainfall patterns in the eastern part of India are responsible for the changing water regime.  Impact of de-glaciation on the water resources of the Himalayan region and change in local water discharges can respond to future climate scenarios. This may results in increased water availability in some river basins and decreased water supplies in other regions in the coming decades.  The glacial fed rivers of Uttarakhand are an important resource for the Ganga basin with many rivers contributing to the irrigation potential of some of India’s most densely populated states like Uttar Pradesh, Bihar, Delhi, Haryana etc.

LOSS OF GLACIERS, RUNOFF AND RIVER FLOW  A very robust finding of hydrological impact studies is that warming leads to change in the seasonality of river flows where much winter precipitation currently falls as snow. Many rivers draining glaciated regions, particularly in the Hindu KushHimalaya are sustained by glacier melt during the summer season.  Higher temperatures generate increased glacier melt. As these glaciers retreat due to global warming, river flows are increased in the short term, but the contribution of glacier melt will gradually decrease over the next few decades.  In the higher reaches of Himalayas, snowfall builds up from year to year to form glaciers that provide long-term reservoirs of water stored as ice. The Himalayan range has a total area of 35,110 sq. km of glacier and ice cover, with a total ice reserve of 3,735 cu. Km.  Climate controls river flow and glacier mass balance in the Himalayan region, and these vary considerably from west to east. The variations in the hydrological cycles of rivers in India are determined mainly by the seasonality of the precipitation and the temperature, which governs the ratio between snow and rainfall. It is found that annual snowmelt run off, glacier melt run-off o and total stream flow increase linearly with change in temperature (1-3 C), but the most prominent effect of increase in temperature has been noticed on glacier melt run off.

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FLOODING AND FLOOD FREQUENCY  A warmer climate, with its increased climate variability, will increase the risk of floods. As there are a number of climatic and non-climatic drivers influencing flood impacts, the realization of risks depends on several factors. Floods include river floods, flash floods, urban floods and sewer floods, and can be caused by intense and/or long-lasting precipitation, snowmelt, dam break, or reduced conveyance due to ice jams or landslides. :: Floods depend on precipitation intensity, volume, timing, antecedent conditions of rivers and their drainage basins (e.g., presence of snow and ice, soil character, wetness, urbanization, and existence of dikes, dams, or reservoirs). Human encroachment into flood plains and lack of flood response plans increase the damage potential.  With more than one-sixth of the Earth’s population relying on melt water from glaciers and seasonal snow packs for their water supply, the consequences of projected changes for future water availability, predicted with high confidence and already diagnosed in some regions, will be adverse and severe. :: Drought problems are projected for regions, which depend heavily on glacial melt water for their main dry-season water supply. Rapid melting of glaciers can lead to flooding of rivers and to the formation of glacial melt-water lakes, which may pose a serious threat of outburst floods. The entire Hindu Kush-Himalaya ice mass has decreased in the last two decades. Hence, water supply in areas fed by glacial melt water from the Himalayas, on which millions of people in India depend, will be negatively affected.

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PROJECTED FACTS  The wheat, which is generally grown in the winter, is more likely to be affected than rice. Reductions in wheat production as a result of climate change are predicted to be more pronounced for rain fed crops (as opposed to irrigated crops) and under limited water supply situations because there are no coping mechanisms for rainfall variability.  The difference in yield is influenced by baseline climate. In sub tropical environments the decrease in potential wheat yields ranged from 1.5 to 5.8%, while in tropical areas the decrease was relatively higher, suggesting that warmer regions can expect greater crop losses.  The increases in temperature (by about 2ºC) reduced potential grain yields of wheat in most places in India. Reductions in yields as a result of climate change are predicted to be more pronounced for rainfed crops (as opposed to irrigated crops) and under limited water supply situations because there are no coping mechanisms for rainfall variability.  Overall, temperature increases are predicted to reduce rice yields. An increase of 2-4ºC is predicted to result in a reduction in yields.  Eastern regions are predicted to be most impacted by increased temperatures and decreased radiation, resulting in relatively fewer grains and shorter grain filling durations. By contrast, potential reductions in yields due to increased temperatures in Northern India are predicted to be offset by higher radiation, lessening the impacts of climate change.  Although additional CO2 can benefit crops, this effect was nullified by an increase of temperature.

COASTAL ZONE  The coastal zone is an important and critical region for India. More than 100 million people of the Indian population live along 2 the 7510 km country’s coasts, with an average population density of 455 persons per km which is about 1.5 times the national average of 324 (Census, 2001).  Climate change effects on sea level can impact coastal areas in two ways – through increase in mean sea level, and through increased frequency and intensity of coastal surges and storms.  Climate change is of concern to India in view of the damages that occur along the east coast of India from the cyclones that form in the Bay of Bengal. Any increase in the frequency or intensity of tropical disturbances due to climate change in the future could cause increased damages to life and property in the coastal regions.  Future climate change in the coastal zones is likely to be manifested through the worsening of climate related problems like erosion, flooding, subsidence and deterioration of coastal ecosystems. The key climate related risks in the coastal zone includes tropical cyclone, sea level rise, and changes in temperature and precipitation.  It is expected that a rise in global temperatures will bring a rise in sea levels, with adverse impact. The observed trends in the mean sea level along the Indian coast indicate a rising of about one centimeter per decade, which is close to that noticed in

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[BestCurrentAffairs.com's Book for IAS Prelims 2022] other parts of the globe. The projected future sea level rise could inundate low-lying areas, coastal marshes and wetlands erode beaches and increase flooding and salinity of rivers, bays and aquifers.

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SEA-LEVEL RISE  Climate warming will lead to thermal expansion of water and melting of glacier and polar land ice, with a subsequent rise in sea level. The effects of sea-level rise will vary with location, speed of the rise, and the geological and biological responses of the affected ecosystems.  Using the available models, global sea-level rise of 10-25 cm per 100 years has been predicted due to the emission of GHGs. A rise in sea level has significant implications on the coastal population and agricultural performance of India. According to India’s NATCOM report variety of impacts are expected which include:  Land loss and population displacement.  Increased flooding of low-lying coastal areas.  Agricultural impacts (like, loss of yield & employment) resulting from inundation, salinization, and land loss.  Impacts on coastal aquaculture.  Impacts on coastal tourism, particularly the erosion of sandy beaches.  Sea level rise will affect many regions, with the Andaman and Nicobar Islands, the Lakshadweep island in the south western part, the low lying deltaic region in West Bengal, and the Couch region in Gujarat are likely to be the most vulnerable area.  Additionally, increased occurrence of extreme events due to climate change will also affect the poor the most as their adoptive capacities are less. The coastal zone in India is frequently affected by cyclones and sea level rise is going to be an area o f concern for the country.

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DESERT  Deserts are unique, naturally occurring environments characterized by low and irregular rainfall (less than 100 mm a year on average) and extreme temperatures. The dry conditions found in deserts have resulted in a limited number of human inhabitants. Despite this, deserts sustain a diverse range of plants and animals as many species including reptiles and mammals have developed ingenious ways to cope with the extremes.  Among the findings of UNEP’s Global Desert Outlook, climate change impacts are listed as the greatest threat. Climate change O O over the past 25 years has caused temperatures to rise faster in the deserts, up to 2 C, than the global average of 0.45 C. O The study found also that most deserts will see temperature rise by 5-7 C by the end of the century and rainfall drop 10-20%. According to UNEP these vast open spaces, home to rare and useful plants and animals, are at risk from climate change and human exploitation.

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IMPACT ON INDIAN DESERT  The arid western part of Indian subcontinent, including the western part of Rajasthan state, containing the Thar Desert is likely to experience large scale changes due to changing climatic conditions. The region is already witnessing subtle change in rainfall. The spatial patterns of changes in rainfall and temperature in arid western part of India suggest the likely evolution of 3 major sub zones in the regions climate.  The hotter and very dry north west Rajasthan and adjoining Punjab  The warmer and moderately wetter arid Gujarat and adjoining Rajasthan  The hotter and slightly wetter eastern fringe of arid Rajasthan and adjoining Haryana  These patterns are not encouraging for agriculture related activities in most part of the Indian desert and its fringes. Higher temperature in association with reduced rainfall will desiccate the soil further and reduce chances of crop survival. Considering that the north western part of the desert is likely to far drier than northwestern part of the desert is likely to be far drier than at present. It is high time to identify appropriate adaptation options

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ALGAL BLOOMS IN NEWS  An algal bloom is a rapid increase or accumulation in the population of algae (typically microscopic) in an aquatic system. Algal blooms may occur in freshwater as well as marine environments. Typically, only one or a small number of phytoplankton species are involved, and some blooms may be recognized by discoloration of the water resulting from the high density of pigmented cells.  Although there is no officially recognized threshold level, algae can be considered to be blooming at concentrations of hundreds to thousands of cells per milliliter, depending on the severity. Algal bloom concentrations may reach millions of cells per milliliter. Algal blooms are often green, but they can also be other colors such as yellow-brown or red, depending on the species of algae.  Bright green blooms are a result of cyanobacteria (colloquially known as blue-green algae) such as Microcystis. Blooms may also consist of macroalgal (non-phytoplanktonic) species. These blooms are recognizable by large blades of algae that may wash up onto the shoreline.  Of particular note are harmful algal blooms (HABs), which are algal bloom events involving toxic or otherwise harmful phytoplankton such as dinoflagellates of the genus Alexandrium and Karenia, or diatoms of the genus Pseudo-nitzschia. Such blooms often take on a red or brown hue and are known colloquially as red tides.  FRESHWATER ALGAL BLOOMS: Freshwater algal blooms are the result of an excess of nutrients, particularly phosphorus. The excess of nutrients may originate from fertilizers that are applied to land for agricultural or recreational purposes; these nutrients can then enter watersheds through water runoff. Excess carbon and nitrogen have also been suspected as causes.  When phosphates are introduced into water systems, higher concentrations cause increased growth of algae and plants. Algae tend to grow very quickly under high nutrient availability, but each alga is short-lived, and the result is a high concentration of dead organic matter which starts to decay. The decay process consumes dissolved oxygen in the water, resulting in hypoxic conditions. Without sufficient dissolved oxygen in the water, animals and plants may die off in large numbers.  Blooms may be observed in freshwater aquariums when fish are overfed and excess nutrients are not absorbed by plants. These are generally harmful for fish, and the situation can be corrected by changing the water in the tank and then reducing the amount of food given.  HARMFUL ALGAL BLOOMS: A harmful algal bloom (HAB) is an algal bloom that causes negative impacts to other organisms via production of natural toxins, mechanical damage to other organisms, or by other means. HABs are often associated with large-scale marine mortality events and have been associated with various types of shellfish poisonings.

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HARMFUL ALGAL BLOOM IN INDIA: Harmful algal blooms (HAB), lethal for human beings and marine ecosystems alike, are steadily increasing in intensity in the Indian waters. Researchers have found out that the toxic blooms had increased by around 15 % over the last 12 years in Indian seas. There were 80 harmful blooms between 1998 and 2010 in the Indian seas against the 38 that took place between 1958 and 1997. The number of such blooms was just 12 between 1917 and 1957. MONITORING: The researchers had monitored the harmful blooms and tried to identify the factors causing the bloom, dynamics of bloom formation, spread and its ecological consequences on marine ecosystems. The potentially toxic micro algae recorded from the Indian waters included Alexandrium, Gymnodinium, Dinophysis, Coolia monotis, Prorocentrum lima and Pseudo-nitzschia. Toxic blooms have been reported from over 30 countries, including India. The first recorded observation on algal blooms in India was in 1908.

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CLIMATE RESEARCH Modern research into climatic variation and change is based on a variety of empirical and theoretical lines of inquiry. One line of inquiry is the analysis of data that record changes in atmosphere, oceans, and climate from roughly 1850 to the present. In a second line of inquiry, information describing paleo-climatic changes is gathered from “proxy,” or indirect, sources such as ocean and lake sediments, pollen grains, corals, ice cores, and tree rings. Finally, a variety of theoretical models can be used to investigate the behavior of Earth’s climate under different conditions. These three lines of investigation are described in this section.

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Modern observations;  Although a limited regional subset of land-based records is available from the 17th and 18th centuries, instrumental measurements of key climate variables have been collected systematically and at global scales since the mid-19th to early 20th centuries.  These data include measurements of surface temperature on land and at sea, atmospheric pressure at sea level, precipitation over continents and oceans, sea-ice extents, surface winds, humidity, and tides.  Such records are the most reliable of all available climate data, since they are precisely dated and are based on wellunderstood instruments and physical principles.  Since the 1970s these data have been supplemented by polar-orbiting and geostationary satellites and by platforms in the oceans that gauge temperature, salinity, and other properties of seawater.  Attempts have been made to fill the gaps in early measurements by using various statistical techniques and “backward prediction” models and by assimilating available observations into numerical weather prediction models.  These techniques seek to estimate meteorological observations or atmospheric variables (such as relative humidity) that have been poorly measured in the past.  Modern measurements of greenhouse gas concentrations began with an investigation of atmospheric carbon dioxide (CO2) concentrations by American climate scientist Charles Keeling at the summit of Mauna Loa in Hawaii in 1958.  Keeling’s findings indicated that CO2 concentrations were steadily rising in association with the combustion of fossil fuels, and they also yielded the famous “Keeling curve,” a graph in which the longer-term rising trend is superimposed on small oscillations related to seasonal variations in the uptake and release of CO2 from photosynthesis and respiration in the terrestrial biosphere.  Keeling’s measurements at Mauna Loa apply primarily to the Northern Hemisphere.  Taking into account the uncertainties, the instrumental climate record indicates substantial trends over the past century consistent with a warming Earth.  These trends include a rise in global surface temperature of 0.6 °C (1.1 °F), an associated elevation of global sea level of 17 cm (6.7 inches), and a decrease in snow cover in the Northern Hemisphere of approximately 1.5 million square km (580,000 square miles).  Records of average global temperatures kept by the World Meteorological Organization (WMO) indicated that the years 1998, 2005, and 2010 were statistically tied with one another as the warmest years since modern record keeping began in 1880; the WMO also noted that the decade 2001–10 was the warmest decade since 1880.  Increases in global sea level are attributed to a combination of seawater expansion due to ocean heating and freshwater runoff caused by the melting of terrestrial ice.  Reductions in snow cover are the result of warmer temperatures favoring a steadily shrinking winter season.

THEORETICAL CLIMATE MODELS  Theoretical models of Earth’s climate system can be used to investigate the response of climate to external radiative forcing as well as its own internal variability.  Two or more models that focus on different physical processes may be coupled or linked together through a common feature, such as geographic location.  Climate models vary considerably in their degree of complexity. The simplest models of energy balance describe Earth’s surface as a globally uniform layer whose temperature is determined by a balance of incoming and outgoing shortwave and longwave radiation.  These simple models may also consider the effects of greenhouse gases.  At the other end of the spectrum are fully coupled, three-dimensional, global climate models. These are complex models that solve for radiative balance; for laws of motion governing the atmosphere, ocean, and ice; and for exchanges of energy and momentum within and between the different components of the climate.  In some cases, theoretical climate models also include an interactive representation of Earth’s biosphere and carbon cycle.  Even the most-detailed climate models cannot resolve all the processes that are important in the atmosphere and ocean.  Most climate models are designed to gauge the behavior of a number of physical variables over space and time, and they often artificially divide Earth’s surface into a grid of many equal-sized “cells.”  Each cell may neatly correspond to some physical process (such as summer near-surface air temperature) or other variable (such as land-use type), and it may be assigned a relatively straightforward value. So-called “sub-grid-scale” processes, such as those of clouds, are too small to be captured by the relatively coarse spacing of the individual grid cells.  Instead, such processes must be represented through a statistical process that relates the properties of the atmosphere and ocean. For example, the average fraction of cloud covers over a hypothetical “grid box” (that is, a representative volume of air or water in the model) can be estimated from the average relative humidity and the vertical temperature profile of the grid cell.  Variations in the behaviour of different coupled climate models arise in large part from differences in the ways sub-grid-scale processes are mathematically expressed.

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Despite these required simplifications, many theoretical climate models perform remarkably well when reproducing basic features of the atmosphere, such as the behaviour of midlatitude jet streams or Hadley cell circulation. The models also adequately reproduce important features of the oceans, such as the Gulf Stream. In addition, models are becoming better able to reproduce the main patterns of internal climate variability, such as those of El Niño/Southern Oscillation (ENSO). Consequently, periodically recurring events—such as ENSO and other interactions between the atmosphere and ocean currents—are being modeled with growing confidence. Climate models have been tested in their ability to reproduce observed changes in response to radiative forcing. In 1987 a team at NASA’s Goddard Institute for Space Studies in New York City used a fairly primitive climate model to predict warming patterns that might occur in response to three different scenarios of anthropogenic radiative forcing. Warming patterns were forecasted for subsequent decades. Of the three scenarios, one very closely followed the actual nearsurface air temperature pattern that occurred through the 1990s and into the following decade, and it predicted the temperature rise of roughly 0.5 °C (0.9 °F) that actually took place during that interval. The NASA team also used a climate model to successfully predict that global mean surface temperatures would cool by about 0.5 °C for one to two years after the 1991 eruption of Mount Pinatubo in the Philippines. More recently, so-called “detection and attribution” studies have been performed. These studies compare predicted changes in near-surface air temperature and other climate variables with patterns of change that have been observed for the past one to two centuries. The simulations have shown that the observed patterns of warming of Earth’s surface and upper oceans, as well as changes in other climate phenomena such as prevailing winds and precipitation patterns are consistent with the effects of an anthropogenic influence predicted by the climate models. In addition, climate model simulations have shown success in reproducing the magnitude and the spatial pattern of cooling in the Northern Hemisphere between roughly 1400 and 1850—during the Little Ice Age, which appears to have resulted from a combination of lowered solar output and heightened explosive volcanic activity.

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INTERNATIONAL NEGOTIATIONS  As public concern about changes in the world's climate mounted in the 1980s, the WMO (World Meteorological Organisation) and the UNEP (United Nations Environmental Programme) established the IPCC (Intergovernmental Panel on Climate Change) in 1988 to assess the seriousness of the problem.  The First Assessment Report of the IPCC, completed in 1990, highlighted the global threat of climate change.  In December 1990, the UN General Assembly decided to launch negotiations on what was to become the UNFCCC (United Nations Framework Convention on Climate Change). The negotiations commenced in February 1991 and were concluded in 15 months. The Convention was adopted in May 1992, and opened for signature in Rio at the UN Conference on Environment and Development. It came into force in March, 1994 after being ratified by 50 countries.  In 1997, the Parties to the UNFCCC adopted the Kyoto Protocol, which requires Annex I countries (developed countries and economies in transition) to reduce their overall GHG emissions by 5.2% below their 1990 levels.

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TIMELINE OF NEGOTIATIONS

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1987

1988 1989 1990

Milestone 1st World Climate Conference  Climate as a vital natural resource  Live in harmony with nature  Governments should ‘foresee and prevent potential man-made changes in climate that might be adverse to the well-being of humanity’ Brundtland Commission Report: Need to adopt a sustainable development path that would help meet present needs while leaving enough resources to meet future needs. Precedent set by successful negotiation of Montreal Protocol WMO and UNEP establish IPCC (Intergovernmental Panel on Climate Change) UN General Assembly Resolution calls for global summit on environment and development issues First Assessment Report of IPCC published: UN General Assembly resolution establishes INC (Intergovernmental Negotiating Committee) to draft a framework convention

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February 1991 to May 1992 May 1992 June 1992

21 March 1994

April 1995

December 1995

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Representatives of 160 nations negotiate key issues  Commitments to emission targets  Provisions for technology transfer and financial resources to developing countries INC adopts UNFCCC (United Nations Framework Convention on Climate Change) UNFCCC opened for signature at United Nations Conference on Environment and Development (Rio Earth Summit) UNFCCC comes into force on 21 March 1994 (ratified by 186 countries as of July 2002)  No legally binding targets (Annex I countries to return to 1990 levels by the end of the decade)  Submit National Communications First Conference of Parties (COP-1) in Berlin adopts the Berlin Mandate. New round of negotiations launched on a 'protocol or other legal instrument'  No new commitments for non-Annex I countries  Introduction of Activities Implemented Jointly (AIJ)  voluntary cooperative GHG-mitigation projects IPCC approves its Second Assessment Report. Its findings underline the need for strong policy action.  The balance of evidence suggests a discernible human influence on global climate

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December 1997 March 1998 November 1998

November 1999

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July 1996

 Significant 'no regrets' opportunities available  Potential risk of damage sufficient to justify action beyond 'no regrets' COP-2 in Geneva takes note of the Geneva Ministerial Declaration, which acts as a further impetus to the on-going negotiations  Scientific research provides basis for urgently strengthening action  World faces significant, often adverse impacts from climate change  Legally-binding significant overall reductions in GHG emissions to be negotiated by the next COP  COP-3 meeting in Kyoto adopts the Kyoto Protocol to the UN Framework Convention on Climate Change  Kyoto Protocol opened for signature at UN headquarters in New York. Over a one-year period, it receives 84 signatures  COP-4 meeting in Buenos Aires adopts the Buenos Aires Plan of Action setting out a programme of work on the operational details of the Kyoto Protocol and the implementation of the Convention. COP-6 set as deadline for adopting many important decisions  COP-5 in Bonn sets an aggressive timetable to achieve measurable progress by COP-6 on the entry into force of the Kyoto Protocol  COP-6 meets in The Hague, but fails to agree on a package of decisions under the Buenos Aires Plan of Action  COP-6 part II (or COP-6b) resumes in Bonn. Parties adopt the Bonn Agreements, registering political consensus on key issues under the Buenos Aires Plan of Action. They also complete work on a series of detailed decisions, but some remain outstanding  COP-7 in Marrakesh finalizes and formally adopts COP-6 decisions as the Marrakesh Accords  Entry into force of the Kyoto Protocol.  The first Meeting of the Parties to the Kyoto Protocol (MOP 1) takes place in Montreal.  In accordance with Kyoto Protocol requirements, Parties launched negotiations on the next phase of the KP under the Ad Hoc Working Group on Further Commitments for Annex I Parties under the Kyoto Protocol (AWG-KP).  IPCC's Fourth Assessment Report released.  Climate science entered into popular consciousness. At COP13, Parties agreed on the Bali Road Map, which charted the way towards a post-2012 outcome in two work streams: the AWG-KP, and another under the Convention, known as the Ad-Hoc Working Group on Long-Term Cooperative Action under the Convention.  Copenhagen Accord drafted at COP15 in Copenhagen. This was taken note of by the COP.  Countries later submitted emissions reductions pledges or mitigation action pledges, all non-binding.  The Durban Platform for Enhanced Action drafted and accepted by the COP, at COP17.  Cancun Agreements drafted and largely accepted by the COP, at COP16.  The Doha Amendment to the Kyoto Protocol is adopted by the CMP at CMP8. More on the Doha Amendment.  Several decisions taken opening a gateway to greater ambition and action on all levels.  COP 19 was the 19th yearly session of the Conference of the Parties (COP) to the 1992 United Nations Framework Convention on Climate Change (UNFCCC) and the 9th session of the Meeting of the Parties (CMP) to the 1997 Kyoto Protocol (the protocol having been developed under the UNFCCC's charter).  The conference was held in Warsaw, Poland from 11 to 23 November 2013.  Key decisions adopted at COP19/CMP9 include decisions on further advancing the Durban Platform, the Green Climate Fund and Long-Term Finance, the Warsaw Framework for REDD Plus and the Warsaw International Mechanism for Loss and Damage.  On 1–12 December 2014, Lima, Peru hosted the 20th yearly session of the Conference of the Parties (COP) to the 1992 United Nations Framework Convention on Climate Change (UNFCCC) and the 10th session of the Meeting of the Parties (CMP) to the 1997 Kyoto Protocol (the protocol having been developed under the UNFCCC's charter).  The pre-COP conference was held in Venezuela.  The COP 21 was held in Paris from 30 November to 12 December 2015.  Negotiations resulted in the adoption of the Paris Agreement on 12 December, governing climate change reduction measures from 2020.  The adoption of this agreement ended the work of the Durban platform, established during COP17. The agreement will enter into force (and thus become fully effective) on November 4, 2016.  On October 4, 2016 the threshold for adoption was reached with over 55 countries representing at least 55% of the world's greenhouse gas emissions ratifying the Agreement.

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COP 22 was held in Marrakech, in the North-African country of Morocco, on 7– 18 November 2016.  A focal issue of COP 22 is that of water scarcity, water cleanliness, and waterrelated sustainability, a major problem in the developing world, including many African states.  Prior to the event a special initiative on water was presided by Charafat Afailal, Morocco’s Minister in Charge of Water and Aziz Mekouar, COP 22 Ambassador for Multilateral Negotiations.  COP 23 was held on 6–17 November 2017 in Bonn, Germany.  It marked the opening of the Talanoa Dialogue. This allows countries to informally take stock of progress towards the Paris Agreement’s goals, without any sense of judgement. Countries agreed to create more space for Suva expert dialogue. COP 24 was held in December 2018 in Katowice, Poland. Main Outcomes:  The Green Climate Fund planned.  Governments agreed on a mechanism to address loss and damage caused by climate change.  Countries urged voluntary cancellation of Certified Emission Reductions (CERs).  Governments established the Warsaw International Mechanism for Loss and Damage.  Cutting emissions from deforestation - "the Warsaw Framework for REDD+".  Developed countries met the target capitalization of USD 100 million for the Adaptation Fund.  The Climate Technology Centre and Network (CTCN) made open for business. UN Climate Change Conference/ COP25, was the 25th United Nations Climate Change conference. It was held in Madrid, Spain, from 2 to 13 December 2019 under the presidency of the Chilean government. The conference incorporated the 25th Conference of the Parties to the United Nations Framework Convention on Climate Change (UNFCCC), the 15th meeting of the parties to the Kyoto Protocol (CMP15), and the second meeting of the parties to the Paris Agreement (CMA2). The decisions about the carbon market and emissions cuts were delayed to the next climate conference in Glasgow. European Union reached an agreement about The European Green Deal that should lower its emissions to zero by 2050. Climate Ambitious Coalition contains now "73 countries committed to net zero emissions by 2050, as well as a further 1214 actors (regions, cities, businesses, investors) who have pledged the same goal. The 2021 United Nations Climate Change Conference, more commonly referred to as COP26, was the 26th United Nations Climate Change conference, held at the SEC Centre in Glasgow, Scotland, United Kingdom, from 31 October to 13 November 2021.

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2021

IPCC 5TH ASSESSMENT REPORT

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The Fifth Assessment Report (AR5) of the United Nations Intergovernmental Panel on Climate Change (IPCC) is the fifth in a series of such reports. The IPCC was established in 1988 by the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP) to assess scientific, technical and socio-economic information concerning climate change, its potential effects and options for adaptation and mitigation. The Fifth Assessment Report was finalized in 2014. As had been the case in the past, the outline of the AR5 was developed through a scoping process which involved climate change experts from all relevant disciplines and users of IPCC reports; in particular representatives from governments. Governments and organizations involved in the Fourth Report were asked to submit comments and observations in writing with the submissions analysed by the panel. The report was delivered in stages, starting with Working Group I's report on the physical science basis, based on 9,200 peer-reviewed studies. The summaries for policy makers were released for the first report, on 31 March 2014 for the second report entitled "Impacts, Adaptation, and Vulnerability" and on 14 April 2014 for the third report entitled "Mitigation of Climate Change". The Synthesis Report was released on 2 November 2014. It is anticipated that the Fifth Assessment Report will pave the way for a global, legally binding treaty on reducing carbon emissions at the UN Climate Change Conference in Paris during late 2015.

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MODELS  AR5 relies on the Coupled Model Intercomparison Project Phase 5 (CMIP5), an international effort among the climate modeling community to coordinate climate change experiments.  Most of the CMIP5 and Earth System Model (ESM) simulations for AR5 WRI were performed with prescribed CO2 concentrations reaching 421 ppm (RCP2.6), 538 ppm (RCP4.5), 670 ppm (RCP6.0), and 936 ppm (RCP 8.5) by the year 2100.  Climate models have improved since the prior report.  Model results, along with observations, provide confidence in the magnitude of global warming in response to past and future forcing.

PREDICTIONS  Further warming will continue if emissions of greenhouse gases continue. The global surface temperature increase by the end of the 21st century is likely to exceed 1.5 °C relative to the 1850 to 1900 period for most scenarios, and is likely to exceed 2.0 °C for many scenarios. The global water cycle will change, with increases in disparity between wet and dry regions, as well as wet and dry seasons, with some regional exceptions.  The oceans will continue to warm, with heat extending to the deep ocean, affecting circulation patterns.

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Decreases are very likely in Arctic sea ice cover, Northern Hemisphere spring snow cover, and global glacier volume Global mean sea level will continue to rise at a rate very likely to exceed the rate of the past four decades Changes in climate will cause an increase in the rate of CO2 production. Increased uptake by the oceans will increase the acidification of the oceans. Future surface temperatures will be largely determined by cumulative CO2, which means climate change will continue even if CO2 emissions are stopped. The summary also detailed the range of forecasts for warming, and climate impacts with different emission scenarios. Compared to the previous report, the lower bounds for the sensitivity of the climate system to emissions were slightly lowered, though the projections for global mean temperature rise (compared to pre-industrial levels) by 2100 exceeded 1.5 °C in all scenarios.

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IPCC SIXTH ASSESSMENT REPORT

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At its 41st Session in February 2015, the IPCC decided to produce a Sixth Assessment Report (AR6). At its 43rd Session in April 2016, it decided to produce three Special Reports, a Methodology Report and AR6. The Sixth Assessment Report (AR6) of the United Nations (UN) Intergovernmental Panel on Climate Change (IPCC) is the sixth in a series of reports which assess scientific, technical, and socio-economic information concerning climate change. Three Working Groups (WG) assess  I The Physical Science Basis,  II Impacts, Adaptation and Vulnerability and  III Mitigation of Climate Change, of which the first WGI study has been published in 2021 and the other two are planned for 2022. The final synthesis report is due to be finished by late 2022. The first of three working groups (WGI) published Climate Change 2021: The Physical Science Basis on 9 August 2021. A total of 234 scientists from 66 countries contributed to this first of three working group reports. The report's authors built on more than 14,000 scientific papers to produce a 3,949-page report, which was then approved by 195 governments. The Summary for Policymakers (SPM) document was drafted by scientists and agreed to line-by-line by the 195 governments in the IPCC during the five days leading up to 6 August 2021. According to the report, it is only possible to avoid warming of 1.5 °C or 2 °C if massive and immediate cuts in greenhouse gas emissions are made. In a front page story, The Guardian described the report as "its starkest warning yet" of "major inevitable and irreversible climate changes", a theme echoed by many newspapers as well as political leaders and activists around the world. The sixth assessment report is made up of the reports of three working groups (WG I, II, and III) and a synthesis report which concludes the assessment in late 2022.  The Physical Science Basis of Climate Change in August 2021 (WGI contribution)  Impacts, adaptation and vulnerability in February 2022 (WGII contribution)  Mitigation of climate change in March 2022 (WGIII contribution)  Synthesis Report in October 2022 A total of 234 scientists from 66 countries contributed to the first of three working group reports. Working group 1 (WGI) published Climate Change 2021: The Physical Science Basis. According to the report, it is only possible to avoid warming of 1.5 °C or 2 °C if massive and immediate cuts in greenhouse gas emissions are made. The Working Group 1 (WGI) report, Climate Change 2021: The Physical Science Basis comprises thirteen chapters and is focused on the foundational consensus of the climate science behind the causes and effects of human greenhouse gas emissions. The report quantifies climate sensitivity as between 2.5 °C and 4 °C for each doubling of carbon dioxide in the atmosphere, while the best estimate is 3 °C.: SPM-14 In all the represented Shared Socioeconomic Pathways the temperature reaches the 1.5 °C warming limit, at least for some period of time in the middle of the 21st century. SSP1-1.9 is a new pathway with a rather low radiative forcing of 1.9 W/m2 in 2100 to model how people could keep warming below the 1.5 °C threshold. But, even in this scenario, the global temperature peaks at 1.6 °C in the years 2041 – 2060 and declines after. SHARED SOCIOECONOMIC PATHWAYS IN THE IPCC SIXTH ASSESSMENT REPORT SSP Scenario Estimated Estimated Very likely range warming warming in °C (Likelihood ) (2041– (2081– (2081–2100) 2060) 2100) SSP1very low GHG emissions: 1.6 °C 1.4 °C 1.0 – 1.8 1.9 CO2 emissions cut to net zero around 2050 SSP1low GHG emissions: 1.7 °C 1.8 °C 1.3 – 2.4 2.6 CO2 emissions cut to net zero around 2075 intermediate GHG emissions (likely): SSP22.0 °C 2.7 °C 2.1 – 3.5 4.5 CO2 emissions around current levels until 2050, then falling but not reaching net zero by 2100 high GHG emissions (unlikely): SSP32.1 °C 3.6 °C 2.8 – 4.6 7.0 CO2 emissions double by 2100 very high GHG emissions (highly unlikely): SSP52.4 °C 4.4 °C 3.3 – 5.7 8.5 CO2 emissions triple by 2075

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According to AR6 coauthors, the probable temperature rise is in the middle of the scenario spectrum that reaches from 1.5 °C to 5 °C, at about 3 °C at the end of the century. It is likely that 1.5 °C will be reached before 2040. The threats from comp ound impacts are rated higher than in previous IPCC reports. The famous hockey stick graph has been extended. Extreme weather is expected to increase in line with temperature, and compound effects (such as heat and drought together) may impact more on society. The report includes a major change from previous IPCC in the ability of scientists to attribute specific extreme weather events.

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The global carbon budget to keep below 1.5 °C is estimated at 500 billion more tonnes of greenhouse gas, which would need the whole world to be net zero before 2050. Staying within this budget, if counting from the beginning of the year 2020, gives a 50% chance to stay below 1.5 °C. For having a 67% chance, the budget is 400 billion tonnes and for a 83% chance it is 300 billion tonnes.: SPM-38f The report says that rapidly reducing methane emissions is very important, to make short-term gains to buy time for carbon dioxide emission cuts to take effect.  Any future warming will increase the occurrence of extreme weather events. Even in a 1.5 °C temperature rise there will be "an increasing occurrence of some extreme events unprecedented in the observational record". The likelihood of more rare events increases more.: SPM-19  The frequency, and the intensity of such events will considerably increase with warming, as described in the following table:: SPM-23 Increase in frequency and intensity of extreme events with global warming Name of event Climate in 1 °C warming 1.5 °C warming 2 °C warming 4 °C warming 1850 - 1900 1 in 10 years Normal 2.8 times more 4.1 times more 5.6 times more 9.4 times more heatwave often, 1.2 °C hotter often, 1.9 °C hotter often, 2.6 °C hotter often, 5.1 °C hotter 1 in 50 years Normal 4.8 times more 8.6 times more 13.9 times more 39.2 times more heatwave often, 1.2 °C hotter often, 2.0 °C hotter often, 2.7 °C hotter often, 5.3 °C hotter 1 in 10 years heavy Normal 1.3 times more 1.5 times more 1.7 times more 2.7 times more precipitation event often, 6.7% wetter often, 10.5% wetter often, 14.0% wetter often, 30.2% wetter 1 in 10 years drought Normal 1.7 times more 2.0 times more 2.4 times more 4.1 times more often, 0.3 sd drier often, 0.5 sd drier often, 0.6 sd drier often, 1.0 sd drier

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