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Climate Change: The Background |
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| The scientific evidence is clear: the earth's climate is changing. The atmosphere is warming and this trend will continue. Because of the complexity of atmospheric and oceanic currents this warming will produce violent storms, drought and floods and other not-yet-predictable weather events. Already several examples of atmospheric warming are available from around the globe. For example, nine of the hottest years recorded in more than a century have occurred since 1988 (1). Worldwide, July 1998 was the hottest month ever (2). In 1998 India experienced its worst hot spell in 50 years, which took a toll of over 3,000 lives (3). Another startling phenomenon is the retreat of the Himalayan Glaciers—18 m per year in the case of Gangotri (4). These changes are happening because humans have released various heat-absorbing gases into the atmosphere--mainly through burning fossil fuels. | |
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For the past two decades scientists have been collecting and debating evidence of long-term climate change. Are the observed warming trends simply natural variations in climate or are they a long- term trend? And if there is a trend what is causing it--human activity or natural fluctuations? In 1988 the United Nations set up the Intergovernmental Panel on Climate Change (IPCC)—an official scientific body comprised of leading atmospheric |
Global Mean Surface Air Temperatures, 1865-1995
Source:World Resources Institute (www.wri.org) |
| scientists to
investigate climate change. IPCC’s Second Assessment Report published
in 1995 states that climate change is a long-term trend, and human
activities are its major cause. At the root of this is the human use of
fossil fuels. When burnt they release what are called greenhouse gases (GHGs).
However, the release of key GHGs--carbon dioxide, methane, and nitrous oxide--is not only due to the burning of fossil fuels. It is also a part of nature’s normal processes. Like the panes of a greenhouse, GHGs allow sunlight to pass through the troposphere (lower atmosphere), but trap the heat. As the heat rises from the earth’s surface, into the troposphere, some of this heat escapes into space, some is reflected back to the surface by the molecules of GHGs, warming the air. This natural trapping of heat, or the greenhouse effect, has made earth habitable. Without it the earth would have been a cold, lifeless planet Thus in the normal scheme of things GHGs, which make up less than 1 per cent of the atmosphere, are benign. Their levels in the atmosphere are determined by a balance between "sources" (processes which release these gases) and "sinks" (processes which absorb or remove them). But a lot of modern human activity tends to disrupt this optimal balance. Such disruption may happen by way of introducing new or additional sources of natural GHGs, of manmade GHGs such as CFCs and their substitutes, or of interference with natural sinks. The enhanced levels of GHG accumulation in the atmosphere resulting from this disruption are the cause of Global Warming and Climate Change. Levels of greenhouse gases are rising as a direct result of human activity. Additions by human activity can significantly affect the amount of heat trapped in the atmosphere over time, and most of these gases have fairly long life spans ranging from ten to thousands of years. What we put into the atmosphere today will therefore continue to warm the planet for a long time to come Potent warmers of the globe (sources of gases) Carbon dioxide (CO2) is responsible for over 60 per cent of the current global warming from GHGs produced by human activities since preindustrial times (around 1750). Its concentration since then has increased by more than 30 per cent and currently increases by 1 per cent every year. The main sources (75 per cent) are the burning of fossil fuels, particularly coal, and increasingly, motor vehicle exhaust. Deforestation and biomass burning contribute 25 per cent. CO2 remains in the atmosphere for around 200 years. Methane (CH4) can trap 20 to 25 times more heat than CO2 on a molecule for molecule basis. It is produced by decomposition of organic matter in rice paddies, natural wetlands, landfills, intestines of cattle, sheep and termites, and in natural gas leaks. Its concentration has doubled since preindustrial times. It stays in the atmosphere for only 10-12 years, but it is removed when it reacts with the hydroxyl (OH) radical to form CO2 (3). Nitrous oxide (N2O) can trap 200 times more heat than CO2 on a molecule for molecule basis and has a life span of 120 to 190 years (1, 5). It is released from a variety of sources including the burning of biomass and coal, the application of nitrogen fertilizers, and from nylon production. Its concentration is growing by 0.25 per cent per year. Chlorofluorocarbons (CFCs) can trap 1,500 to 1,700 times more heat than CO2 on a molecule for molecule basis and remain in the atmosphere for several thousand years. The main sources are leaking refrigerants, industrial solvents, aerosol propellants and production of plastic foams. Their concentration had been growing by 4 per cent per year in the 1990s, but their use is now being phased out under the Montreal Protocol because of their ozone-depleting properties. As a result, CFCs are not included within the scope of the Framework Convention or the Kyoto Protocol. The substitutes developed for CFCs do not directly destroy ozone in the earth’s atmosphere but do contribute to global warming. Hydroflurocarbon gases (HFCs) are a manmade alternative for CFCs for use in refrigeration, as agents used to blow foams or insulation, and as solvents or cleaning agents specially in semiconductor manufacturing. Their global warming potential is, however, 4,000 to 10,000 times that of CO2. Perfluorocarbons (PFCs) are replacement gases for CFCs, but are also a by-product of aluminium smelting. Small amounts are also produced during the uranium enrichment process. They can trap 6,000 to10,000 times more heat than CO2 as GHGs (5). Sulphur hexafluoride (SF6) is a manmade gas used as insulating material for high-voltage equipment such as circuit breakers. It is also used for detecting water leaks in cable cooling systems. It can trap 25,000 times more heat than CO2 (5). Although at present the CFC substitutes listed above contribute little to global climate change, the projected growth in their use could contribute to it significantly in the 21st century (6). Share of greenhouse warming due to different greenhouse gases
Source:World Resources Institute (www.wri.org)
How much have greenhouse gases increased? Concentration of greenhouse gases in the atmosphere has continued to increase. Atmospheric concentrations of CO2, CH4 and N2O have increased by 30 per cent, 145 per cent and 15 per cent respectively since preindustrial times. CO2 concentration, for example, has increased from 280 ppmv (parts per million by volume) in the 1750s to almost 360 ppmv in 2000. The IPCC has set 450 ppmv as the top concentration at which greenhouse gases should be stabilized by the end of the 21st century (6). Most scientists agree that the earth's mean temperature has risen by at least 0.6ОC over the last 120 years. Global warming will lead to a rise in mean sea levels as water expands when heated. The earth's average sea level is expected to rise by about 50 cm by 2100, flooding many low-lying islands and coastal areas. Some of them, such as many islands of the Maldives and large parts of southern Bangladesh, may even become permanently submerged. The energy imbalance in the climate system caused by global warming will result in more violent weather events, increasing the threat of drought and floods (already a major factor due to other kinds of environmental degradation) and intense storms. Global warming also poses serious threats to food production, fresh water sources and human health. Tropical diseases such as malaria could spread to formerly temperate zones, affecting 60 per cent of humanity. Sea level rise and changing weather patterns could trigger large-scale migration from more seriously affected areas. By 2050 global warming could produce as many as 150 million environmental refugees, most of whom would migrate to other countries, causing social tensions and political instability (7). All these consequences of global warming will translate into huge financial costs. Scientist estimate that just to stabilize the levels of CO2 in the atmosphere at their current levels, current global emissions will have to be cut by 60 to 80 percent. But projections suggest that between 1990 and 2010 CO2 emissions will increase by nearly 50per cent (7). Recognizing climate change as a serious global problem, countries of the world got together to discuss what could be done to check the threat. The First World Climate Conference was held in 1979. A formal system of governmental negotiations to tackle the problem was subsequently initiated which resulted in the UN Framework Convention on Climate Change. The legally- binding Kyoto Protocol requiring industrialized countries to make GHG emission reductions is currently open for ratification. It is not yet clear when it will come into force.
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