CLOUD COMMUNICATION POLLUTION MAY HARM OUR CLOUDS
Polar high; little year-round precipitation Sub-polar low; precipitation year round Dry summers; wet winters Sub-tropical high; dry year round Dry winters; wet summers
Equatorial low; ample year-round precipitation
Dry winters; wet summers Sub-polar low; precipitation year round Polar high; little year-round precipitation
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CLOUD COMMUNICATION
CLOUD COMMUNICATION POLLUTION MAY HARM OUR CLOUDS
CLOUD COMMUNICATION POLLUTION MAY HARM OUR CLOUDS
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POLLUTION MAY HARM OUR CLOUDS
CLOUD COMMUNICATION COPYRIGHT © 2015 All Rights Reserved. No part of this book may be reproduced in any form or by any electronic or mechanical means, including information storage and retrieval systems, without permission in writing from the publisher, except by a reviewer who may quote brief passages in a review. ©2015 Houghton Mifflin Harcourt. All rights reserved. Terms of Use Privacy Policy Children’s Privacy Policy Student (K-12) Privacy Policy Sitemap Printed in the United States
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01 How Does Air Pollution Affect Clouds?
IN DEDICATION To Ilan Koren, planetary scientist at the Weizmann Institute of Science in Israel.
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CLOUD COMMUNICATION POLLUTION MAY HARM OUR CLOUDS
INTRODUCTION BY ALINA BRADFORD Pollution is the process of making land, water, air or other parts of the environment dirty and unsafe or unsuitable to use. This can be done through the introduction of a contaminant into a natural environment, but the contaminant doesn’t need to be tangible. Things as simple as light, sound and temperature can be considered pollutants when introduced artificially into an environment. Toxic pollution affects more than 200 million people worldwide, according to Pure Earth, a non-profit environmental organization. In some of the world’s worst polluted places, babies are born with birth defects, children have lost 30 to 40 IQ points, and life expectancy may be as low as 45 years because of cancers and other diseases. Read on to find out more about specific types of pollution.
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TABLE OF CONTENTS 09 NTRODUCTION 013
CHAPTER 1
014 021
CHAPTER 2
THE ANSWER COULD HELP CLARIFY AEROSOLS
022
AEROSOL SOURCES, COMPOSITION,
026
HOW IS HUMAN-CAUSED AIR POLLUTION CHANGING OUR CLIMATE?
029
CHAPTER 3
030 037
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HOW DOES AIR POLLUTION AFFECT CLOUDS?
CHAPTER 4
AIR POLLUTION CAN PREVENT RAINFAL URBAN AND INDUSTRIAL AIR POLLUTION CAN STIFLE RAIN POLLUTION ENHANCED THUNDERSTORMS
038
POLLUTION TEAMS WITH THUNDERCLOUDS TO WARM ATMOSPHERE
043
TO MORE REALISTICALLY MODEL CLOUDS
044
THE SPRINGTIME
046
BIBLIOGRAPHY
049
COLOPHON
CLOUD COMMUNICATION
CLOUD COMMUNICATION
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01 How Does Air Pollution Affect Clouds?
HOW DOES AIR POLLUTION AFFECT CLOUDS? AEROSOLS ARE KEY IN WHIPPING UP A CLOUD, A PROCESS THAT BEGINS WITH THE SUN.
01 How Does Air Pollution Affect Clouds?
01
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THE ANSWER COULD HELP CLARIFY
Few clouds used to populate our skies before the Industrial Revolution, and pollutants spewed by factories since then have vastly increased the cloudiness of our atmosphere.
HOW WARM CLIMATE CHANGE MIGHT GET Deadening calm fills the Horse Latitudes, where there’s ocean, sky and little else. A satellite peers down, capturing wisps of cloud, counting particles suspended in the air, measuring rainfall and monitoring weather. There is little wind. These latitudes, between 30 and 35 degrees away from the equator, are so calm that Spanish sailors in the 17th century could not move their heavily laden ships, or so the legend goes. So, the sailors dumped their cargo— horses—into the subtropical ocean and heaved on. But they left the place with a name: Horse Latitudes. These windless tracts have yielded a new hypothesis relevant to climate science: Few clouds may have populated our skies before the Industrial Revolution, and pollutants spewed by factories since then may have vastly increased the cloudiness of our atmosphere. The results were published yesterday in the journal Science.
CLOUD COMMUNICATION
POLLUTION MAY HARM OUR CLOUDS
The finding cuts to the heart of uncertainty contained in climate models today. Most scientists agree that humans are releasing massive quantities of carbon dioxide into the atmosphere and causing global temperatures to rise. But they disagree on the rate of warming. A doubling of CO2 concentrations could warm the planet by between 2 and 4.5 degrees Celsius, according to the Intergovernmental Panel on Climate Change (IPCC). Part of the uncertainty is due to clouds. They come in various shapes and types, as most people know—puffy popcorns (cumulus); loose brush strokes of mostly ice (cirrus); towering, dark monsters of thunderstorms (cumulonimbus) and many others. Clouds can either reflect the sun’s incoming rays back into space, cooling the Earth. Or they can act as a sheath and trap heat close to the Earth’s surface, warming the planet. Often, they do a little of both. And they do it incredibly well. Clouds have the ability to heat the planet much more than CO2, depending on the type of cloud, its geography and its altitude. And to make things more complicated, cloud particles can have various sizes, shapes and various traits. Translating these into predictions about the overall effect of clouds on the climate can be quite difficult.
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01 How Does Air Pollution Affect Clouds?
01 How Does Air Pollution Affect Clouds?
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US Air Pollution 1980-2013 20% 0% Ozone
PM2.5
Relativ e Level
-20% PM10
-40% Sulfur Dioxide
-60% -80%
Nitrogen Dioxide Carbon Monoxide
Lead
-100% 1980
1985
1990
1995
2000
2005
2010 EPA (2014)
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01 How Does Air Pollution Affect Clouds?
01 How Does Air Pollution Affect Clouds?
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02 Aerosols
AEROSOLS SMALL PARTICLES SUSPENDED IN THE EARTH’S ATMOSPHERE
02 Aerosols
02
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POLLUTION MAY HARM OUR CLOUDS
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Small particles suspended in the Earth’s atmosphere (aerosols) include fine aerosols such as pollution and smoke (red) and coarse aerosols such as dust and sea-salt (green). Image shows aerosol levels on April 13, 2001 as seen by a NASA satellite.
AEROSOL SOURCES, COMPOSITION, AND REMOVAL PROCESSES Worldwide, most atmospheric aerosol particles are produced by ‘natural’ processes such as grinding and erosion of land surfaces resulting in dust, salt-spray formation in oceanic breaking waves, biological decay, forest fires, chemical reactions of atmospheric gases, and volcanic injection. Some particles, on the other hand, have human origins—industry, agriculture, transport (including aviation), and construction. The composition of atmospheric aerosol particles varies widely depending on their source—they may contain salts (predominantly sulfates), minerals (such as silicon), organic materials, and, in most cases, water. The particles grow by absorbing water vapor and other gases. If the relative humidity is sufficiently high (usually about 80 percent or more), tiny water drops can form on some of the particles. A subset of these, called ‘cloud condensation nuclei,’ then grow into cloud drops, which eventually fall to the surface as rain or snow, depositing the particles on land or in the ocean. At higher altitudes, cloud ice particles form on some insoluble particles, such as dust. Although dust plumes from the Sahara and Gobi deserts can be seen circling most of the globe in satellite pictures, aerosol particles in the lower troposphere (the lowest layer of the atmosphere where weather occurs) are usually removed from the atmosphere by settling and precipitation within several days to weeks after they were produced. Their impacts, then, are fairly localized. In the stratosphere (the atmosphere layer above the troposphere), chemical reactions of gases from volcanoes produce sulfate particles that can remain for one or more years, spreading over much of the globe. Although we are familiar with local particulate ‘air pollution’ due to human activities, the fact that atmospheric particles of both natural and human origin have substantial influence on our climate is less widely understood.
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02 Aerosols
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POLLUTION MAY HARM OUR CLOUDS [ 24 ]
01 How Does Air Pollution Affect Clouds?
01 How Does Air Pollution Affect Clouds?
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POLLUTION MAY HARM OUR CLOUDS
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HOW IS HUMAN-CAUSED AIR POLLUTION CHANGING OUR CLIMATE? Human-caused particulate air pollution has a relatively minor—and likely decreasing— impact on our climate. Since aerosol particles of human origin both reflect and absorb solar energy as the solar beam travels down through the atmosphere, these particles can diminish the energy that arrives at the Earth’s surface as heat. Scientists estimate that particles produced by human activities have led to a net loss of solar energy (heat) at the ground (by as much as 8 percent in densely populated areas)[5] over the past few decades. This effect, sometimes referred to as ‘solar dimming,’ may have masked some of the late 20th century global warming due to heat-trapping gases. Human activities that result in production of both reflecting and absorbing aerosol particle have been curtailed by legislation and modern technology in many places. The ‘pea soup fogs’ that so bedeviled London in Sherlock Holmes’ day, for example, were caused by particles produced by incomplete combustion of coal. These ‘fogs’ are now a thing of the past, thanks to mandatory scrubbers and other advanced combustion techniques. Clean air regulations in the United States have also decreased particle concentrations considerably. Even today, though, haze clouds seen over urban regions give dramatic proof of the effects of human-induced particles in the United States, while atmospheric soot production is still very high in many parts of Asia. Global warming is primarily caused by emissions of too much carbon dioxide (CO2) and other heat-trapping gases into the atmosphere when we burn fossil fuels to generate electricity, drive our cars, and power our lives. These heat-trapping gases spread worldwide and remain in the atmosphere for decades to centuries. Thus, as we continue to emit these gases, their atmospheric concentrations build up over time. In contrast, atmospheric aerosol particles are largely localized near their sources, and do not linger in the atmosphere for long so that, even if we continue to emit them at current rates, their atmospheric concentrations will not build up markedly over time. Thus the effect of long-lived global warming emissions will far outweigh the cooling effect of short-lived particles.
02 Aerosols
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03 Air Pollution Can Prevent Rainfall
AIR POLLUTION CAN PREVENT RAINFALL URBAN AND INDUSTRIAL AIR POLLUTION CAN STIFLE RAIN AND SNOWFALL,
03 Air Pollution Can Prevent Rainfall
03
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URBAN AND INDUSTRIAL AIR POLLUTION CAN STIFLE RAIN AND SNOWFALL, BECAUSE THE POLLUTION PARTICLES PREVENT CLOUD WATER FROM CONDENSING INTO RAINDROPS AND SNOWFLAKES. The new study, by Daniel Rosenfeld, of the Hebrew University of Jerusalem, presents satellite images and measurements of “pollution tracks” downstream from major urban areas and air pollution sources such as power plants, lead smelters, and oil refineries. The tracks consist of polluted clouds that have shut off virtually all precipitation because they contain abnormally small water droplets. The droplets’ small size is caused by pollution particles that act as “seeding” sites around which cloud moisture condenses. Approximately one million small droplets must collide and coalesce in order to make a precipitation-sized drop-that is, one large enough to fall below the cloud base and reach the ground before evaporating. In polluted clouds, there are too many small droplets and not enough larger ones. These small droplets float in the air with low probability of bumping into each other and merging into raindrops. The smaller droplets are also slower to freeze into ice crystals, resulting in less sleet and snowfall. Because urban and industrial air pollution is a significant problem in many regions of the world, Rosenfeld’s findings suggest that human activity may be affecting rainfall patterns on a global scale. These data are the first direct evidence of how urban and industrial pollution affects rainfall levels, a question scientists have debated for several decades. In fact, some previous studies have concluded that air pollution might increase rainfall, but the debate has continued due to a lack of convincing data.
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03 Air Pollution Can Prevent Rainfall
COLD SMOKE Sulfur Dioxide Nitrogen Oxides Carbon-Dioxide
30%
Efficiency
WARM SMOKE Recycle waste Gases Flares
98%
Efficiency
HOT SMOKE Airborne Soil Sand
27%
Efficiency
03 Air Pollution Can Prevent Rainfall
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Las Vegas Pheonix Tuscon El Paso Fresno
85% 90%
100’-110’
Reno Sacramento
80% 84%
Albuqerque Pueblo Midland
75% 79% 90-100’
Amarillo Los Angeles Lubbock Little Rock
70% 74%
Honolulu
80’-90’
Abilere Miami
65% 69%
70’-80’
Denver Oklahoma City
% of Sunny Days
San Diego
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03 Air Pollution Can Prevent Rainfall
Extreme High Temperatures
Honolulu Los Angeles San Diego
60’-70’ 50‘-60’ 40‘-50’
30‘-40’
20‘-30’ 10’-20’ Extreme Low Temperatures
Midland Miami Denver Reno Sacramento Las Vegas Pheonix Tuscon Fresno Albuquerque El Paso Pueblo Little Rock Oklahoma City Amarillo Abilene
03 Air Pollution Can Prevent Rainfall
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04 Pollution Enhanced Thunderstorms
POLLUTION ENHANCED THUNDERSTORMS WARM THE PLANET?
04 Pollution Enhanced Thunderstorms
04
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POLLUTION TEAMS WITH THUNDERCLOUDS TO WARM ATMOSPHERE NEW SIMULATION STUDY SHOWS THAT ATMOSPHERE WARMS WHEN POLLUTION INTENSIFIES STORMS Pollution is warming the atmosphere through summer thunderstorm clouds, according to a computational study published May 10 in Geophysical Research Letters. How much the warming effect of these clouds offsets the cooling that other clouds provide is not yet clear. To find out, researchers need to incorporate this new-found warming into global climate models. Pollution strengthens thunderstorm clouds, causing their anvil-shaped tops to spread out high in the atmosphere and capture heat — especially at night, said lead author and climate researcher Jiwen Fan of the Department of Energy’s Pacific Northwest National Laboratory. “Global climate models don’t see this effect because thunderstorm clouds simulated in those models do not include enough detail,” said Fan. “The large amount of heat trapped by the pollution-enhanced clouds could potentially impact regional circulation and modify weather systems.” Clouds are one of the most poorly understood components of Earth’s climate system. Called deep convective clouds, thunderstorm clouds reflect a lot of the sun’s energy back into space, trap heat that rises from the surface, and return evaporated water back to the surface as rain, making them an important part of the climate cycle.
04 Pollution Enhanced Thunderstorms
01 How Does Air Pollution Affect Clouds?
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01 How Does Air Pollution Affect Clouds?
01 How Does Air Pollution Affect Clouds?
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04 Pollution Enhanced Thunderstorms
Previous work showed that when it’s not too windy, pollution leads to bigger clouds. This occurs because more pollution particles divide up the available water for droplets, leading to a higher number of smaller droplets that are too small to rain. Instead of raining, the small droplets ride the updrafts higher, where they freeze and absorb more water vapor. Collectively, these events lead to bigger, more vigorous convective clouds that live longer. Now, researchers from PNNL, Hebrew University in Jerusalem and the University of Maryland took to high-performance computing to study the invigoration effect on a regional scale. To find out which factors contribute the most to the invigoration, Fan and colleagues set up computer simulations for two different types of storm systems: warm summer thunderstorms in southeastern China and cool, windy frontal systems on the Great Plains of Oklahoma. The data used for the study was collected by different DOE Atmospheric Radiation Measurement facilities. The simulations had a resolution that was high enough to allow the team to see the clouds develop. The researchers then varied conditions such as wind speed and air pollution. Fan and colleagues found that for the warm summer thunderstorms, pollution led to stronger storms with larger anvils. Compared to the cloud anvils that developed in clean air, the larger anvils both warmed more — by trapping more heat — and cooled more — by reflecting additional sunlight back to space. On average, however, the warming effect dominated.
04 Pollution Enhanced Thunderstorms
POLLUTION MAY HARM OUR CLOUDS
CLOUD COMMUNICATION
To more realistically model clouds on a small scale, such as in this study, researchers use the physics of temperature, water, gases and aerosols — tiny particles in the air such as pollution, salt or dust on which cloud droplets form. In large-scale models that look at regions or the entire globe, researchers substitute a stand-in called a parameterization to account for deep convective clouds. The size of the grid in global models can be a hundred times bigger than an actual thunderhead, making a substitute necessary. However, thunderheads are complicated, dynamic clouds. Coming up with an accurate parameterization is important but has been difficult due to their dynamic nature. Inside a thunderstorm cloud, warm air rises in updrafts, pushing tiny aerosols from pollution or other particles upwards. Higher up, water vapor cools and condenses onto the aerosols to form droplets, building the cloud. At the same time, cold air falls, creating a convective cycle. Generally, the top of the cloud spreads out like an anvil.
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The springtime frontal clouds did not have a similarly significant warming effect. Also, increasing the wind speed in the summer clouds dampened the invigoration by aerosols and led to less warming. This is the first time researchers showed that pollution increased warming by enlarging thunderstorm clouds. The warming was surprisingly strong at the top of the atmosphere during the day when the storms occurred. The pollutionenhanced anvils also trapped more heat at night, leading to warmer nights. “Those numbers for the warming are very big,” said Fan, “but they are calculated only for the exact day when the thunderstorms occur. Over a longer time-scale such as a month or a season, the average amount of warming would be less because those clouds would not appear everyday.” Next, the researchers will look into these effects on longer time scales. They will also try to incorporate the invigoration effect in global climate models. Aerosol indirect effects, i.e., the interactions of aerosols with clouds by serving as cloud condensation nuclei or ice nuclei constitute the largest uncertainty in climate forcing and projection. Previous IPCC reported negative aerosol indirect forcing, which does not account for aerosol-convective cloud interactions because the complex processes involved are poorly understood and represented in climate models. Here we elucidated how aerosols change convective intensity, diabatic heating, and regional circulation under different environmental conditions. We found that aerosol indirect effect on deep convective cloud systems could lead to enhanced regional convergence and a strong top-of-atmosphere warming. Aerosol invigoration effect occurs mainly in warmed-based convection with weak shear. This could result in a strong radiative warming in the atmosphere (up to +5.6 W m−2), a lofted latent heating, and a reduced diurnal temperature difference, all of which could potentially impact regional circulation and modify weather systems. The positive aerosol radiative forcing on deep clouds could offset the negative aerosol radiative forcing on low clouds to an unknown extent.
Heat is then transported upwards by convection, which is done by clouds (cumulus for example) and especially thunderstorms. So, given the amount of energy transport, I’m puzzled as to how they think this new theory works as a net warming, especially when all they are doing is running a model, and providing no hard data.
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04 Pollution Enhanced Thunderstorms
04 Pollution Enhanced Thunderstorms
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BIBLIOGRAPHY HOW DOES AIR POLLUTION AFFECT CLOUDS? By Gayathri Vaidyanathan and ClimateWire June 6, 2014 FEW CLOUDS USED TO POPULATE OUR SKIES BEFORE THE INDUSTRIAL REVOLUTION Credit: Thinkstock June 6, 2014 DOES AIR POLLUTION—SPECIFICALLY PARTICULATE MATTER (AEROSOLS)—AFFECT GLOBAL WARMING?
Wallace, J. M. and P. V. Hobbs. 2006. Atmospheric science: An Introductory Survey (Second edition) (International Geophysics Series), Elsevier, London, UK. SMALL PARTICLES SUSPENDED IN THE EARTH’S ATMOSPHERE Source: NASA. April 13, 2001 HOW IS HUMAN-CAUSED AIR POLLUTION CHANGING OUR CLIMATE? Ramanathan, V. and G. Carmichael. 2008. Global and regional climate changes
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AIR POLLUTION CAN PREVENT RAINFALL
American Association For The Advancement Of Science March 14, 2000
URBAN AND INDUSTRIAL AIR POLLUTION CAN STIFLE RAIN AND SNOWFALL These findings are reported in the 10 March issue of Science. POLLUTION ENHANCED THUNDERSTORMS WARM THE PLANET? Anthony Watts / May 18, 2012 POLLUTION TEAMS WITH THUNDERCLOUDS TO WARM ATMOSPHERE Jiwen Fan, Daniel Rosenfeld, Yanni Ding, L. Ruby Leung, and Zhanqing Li, 2012. AEROSOL INDIRECT EFFECTS, I.E., THE INTERACTIONS May 18, 2012 in Aerosols, Modeling, thunderstorms, Weather. Tags: THE HEAT SOURCE AT THE BASE OF THE ATMOSPHERE Edim May 18, 2012 at 1:28 pm CONCEPTUALIZING EARTH DIFFERENTLY By Carol Rasmussen, NASA’s Earth Science News Team January 26, 2015
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01 How Does Air Pollution Affect Clouds?
COLOPHON FONTS FranklinGothic URW Baskerville Nimbus Sans
3 STAR EPSON PAPER TOOLS Adobe Illustrator Adobe InDesign Adobe Photoshop DESIGNER Paul Lubianker
COLOR PALLETE
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POLLUTION MAY HARM OUR CLOUDS
CONCEPTUALIZING EARTH DIFFERENTLY How much these climate effects will increase in the coming decades is an open question. How much they can be reversed if emissions are reduced in Asia also remains unclear.