Global warming
Revised
The enhanced greenhouse effect
The greenhouse effect is both natural and good – without it there would be no human life on Earth. On the other hand, there are concerns about the enhanced greenhouse effect. The enhanced greenhouse effect is a build up of certain greenhouse gases as a result of human activity. Studies of cores taken from ice packs in Antarctica and Greenland show that the level of CO2 between 10,000 years ago and the midnineteenth century was stable at about 270 ppm. By 1957 the concentration of CO2 atmosphere was 315 ppm. It has since risen to about 360 ppm and is expected to reach 600 ppm by 2050. The increase is due to human activities – primarily the burning of fossil fuels (coal, oil and natural gas) and deforestation. Deforestation of the tropical rainforest also increases atmospheric CO2 levels because it removes the trees that convert CO2 into oxygen.
Greenhouse gases, such as water vapour, CO2, methane, ozone, nitrous oxides and chlorofluorocarbons (CFCs), like the glass on a greenhouse, allow short-wave radiation from the Sun to pass through, but they trap outgoing long-wave radiation, thereby raising the temperature of the lower atmosphere.
2 Atmosphere and weather
2.4 The human impact
Table 2.2 Properties of key greenhouse gases
CO2
Average atmosphereic concentration (ppmv)
Rate of change (% per annum)
355
0.5
Direct global warming potential (GWP) 1
Lifetime (years)
Type of indirect effect
120
None
Methane
1.72
0.6–0.75
11
10.5
Positive
Nitrous oxide
0.31
0.2–0.3
270
132
Uncertain
CFC-11
0.000255
4
3400
55
Negative
CFC-12
0.000453
4
7100
116
Negative
Climate change
Climate change is a very complex issue for a number of reasons: l It involves interactions between the atmosphere, oceans and land masses. l It includes natural as well as anthropogenic forces. l There are feedback mechanisms, not all of which are fully understood. l Many of the processes are long term and so the impact of changes may not yet have occurred.
The effects of increased global temperature
The effects of global warming are very varied. Much depends on the scale of the changes. For example, some impacts could include: l a rise in sea levels, causing flooding in low-lying areas such as the Netherlands, Egypt and Bangladesh – up to 200 million people could be displaced l an increase in storm activity, such as more frequent and intense hurricanes (owing to more atmospheric energy) l 4 billion people suffering from water shortage if temperatures rise by 2°C l 35% drop in crop yields across Africa and the Middle East if temperatures rise by 3°C l 200 million more people could be exposed to hunger if world temperatures rise by 2°C, 550 million if temperatures rise by 3°C l extinction of up to 40% of species of wildlife if temperatures rise by 2°C
Expert tip There are many causes of global climate change. Natural causes include: l variations in the Earth’s orbit around the Sun l variations in the tilt of the Earth’s axis l variations in solar output (sunspot activity) l changes in the amount of dust in the atmosphere (partly due to volcanic activity) l changes in the Earth’s ocean currents as a result of continental drift All of these have helped cause climate change, and may still be doing so, despite anthropogenic (humangenerated) forces.
Paper 1 Core Geography
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