Global Warming - New challenges before the World

Global warming is the increase in the average temperature of the Earth's near-surface, air and oceans and its projected continuation. Global surface temperature increased 0.74 ± 0.18 °C during the last century. The Intergovernmental Panel on Climate Change (IPCC) concludes that increasing greenhouse gas concentrations resulting from human activity such as fossil fuel burning and deforestation are responsible for most of the observed temperature increase since the middle of the twentieth century.

IPCC report indicates that global surface temperature will probably rise a further 1.1 to 6.4 °C during the 21st century. Increasing global temperature will cause sea levels to rise and will change the amount and pattern of precipitation, probably including expansion of subtropical deserts. The continuing retreat of glaciers, permafrost and sea ice is expected, with the Arctic region being particularly affected. Other likely effects include shrinkage of the Amazon rainforest and Boreal forests, increases in the intensity of extreme weather events, species extinctions and changes in agricultural yields.

Political and public debate continues regarding the appropriate response to global warming. The available options are mitigation to reduce further emissions; adaptation to reduce the damage caused by warming; and, more particularly, geo-engineering to reverse global warming. Most national governments have signed and ratified the Kyoto Protocol aimed at reducing greenhouse gas emissions.

Temperature changes vary over the globe. Ocean temperatures increase more slowly than land temperatures because of the larger effective heat capacity of the oceans and because the ocean loses more heat by evaporation. The Northern Hemisphere has more land than the Southern Hemisphere so it warms faster. The Northern Hemisphere also has extensive areas of seasonal snow and sea-ice cover. Although more greenhouse gases are emitted in the Northern than Southern Hemisphere this does not contribute to the difference in warming because the major greenhouse gases persist long enough to mix between hemispheres.

The Earth's climate changes in response to external forces, such as changes in greenhouse gas concentrations, changes in solar luminosity and volcanic eruptions. Climate also changes in response to variations in Earth's orbit around the Sun, but as these orbital cycles vary over thousands of years they are too gradual to have affected temperature changes observed in the past century.

Naturally occurring greenhouse gases have a mean warming effect of about 33 °C. The major greenhouse gases are water vapor, which causes about 36–70 percent of the greenhouse effect (not including clouds); carbon dioxide (CO₂), which causes 9–26 percent; methane (CH₄), which causes 4–9 percent; and ozone, which causes 3–7 percent.

Human activity since the industrial revolution has increased the amount of greenhouse gases in the atmosphere, leading to increased amounts of CO₂, methane, ozone, CFCs and nitrous oxide. The concentrations of CO₂ and methane have increased by 36% and 148% respectively since the mid-1700s. CO₂ concentrations are continuing to rise due to burning of fossil fuels and land-use change. Fossil fuel reserves are sufficient to reach these levels and continue emissions past 2100 if coal and tar sands are extensively exploited.

Greenhouse gases and solar activity affect temperatures in different ways. While both increased solar activity and increased greenhouse gases are expected to warm the troposphere, an increase in solar activity should warm the stratosphere while an increase in greenhouse gases should cool the stratosphere. Observations show that temperatures in the stratosphere have been steady or cooling since 1979, when satellite measurements became available. When ice melts, land or open water takes its place. Both land and open water are on average less reflective than ice and thus absorb more solar radiation. This causes more warming, which in turn causes more melting, and this cycle continues.

Warming is also the triggering variable for the release of methane from sources both on land and on the deep ocean floor, making both of these possible feedback effects. Thawing permafrost, such as the frozen peat bogs in Siberia, creates a positive feedback due to the release of CO₂ and methane.

It usually is impossible to connect specific weather events to global warming. Instead, global warming is expected to cause changes in the overall distribution and intensity of events, such as changes to the frequency and intensity of heavy precipitation. Broader effects are expected to include glacial retreat, Arctic shrinkage and worldwide sea level rise. Other effects may include changes in crop yields, addition of new trade routes, species extinctions, and changes in the range of disease vectors.

Some effects on both the natural environment and human life are, at least in part, already being attributed to global warming. A 2001 report by the IPCC suggests that glacier retreat, ice shelf disruption such as that of the Larsen Ice Shelf, sea level rise, changes in rainfall patterns, and increased intensity and frequency of extreme weather events are attributable in part to global warming. Other expected effects include water scarcity in some regions and increased precipitation in others, changes in mountain snowpack, and adverse health effects from warmer temperatures.

Social and economic effects of global warming may be aggravated by growing population densities in affected areas. Temperate regions are projected to experience some benefits, such as fewer cold-related deaths. A summary of probable effects and recent understanding can be found in the report made for the Report. The newer IPCC Fourth Assessment Report summary reports that there is observational evidence for an increase in intense tropical cyclone activity in the North Atlantic Ocean since 1970, in correlation with the increase in sea surface temperature.

Additional anticipated effects include sea level rise of 0.18 to 0.59 meters in 2090-2100 relative to 1980-1999, repercussions to agriculture, reductions in the ozone layer, increasingly intense hurricanes and extreme weather events, lowering of ocean pH, oxygen depletion in the oceans, and the spread of diseases such as malaria and dengue fever, as well as Lyme disease, hantavirus infections, bubonic plague, and cholera. One study predicts 18% to 35% of a sample of 1,103 animal and plant species would be extinct by 2050, based on future climate projections. However, few mechanistic studies have documented extinctions due to recent climate change and one study suggests that projected rates of extinction are uncertain.

Increased atmospheric CO₂ increases the amount of CO₂ dissolved in the oceans. CO₂ dissolved in the ocean reacts with water to form carbonic acid, resulting in ocean acidification. Ocean surface pH is estimated to have decreased from 8.25 near the beginning of the industrial era to 8.14 by 2004, and is projected to decrease by a further 0.14 to 0.5 units by 2100 as the ocean absorbs more CO₂. Since organisms and ecosystems are adapted to a narrow range of pH, this raises extinction concerns, directly driven by increased atmospheric CO₂, that could disrupt food webs and impact human societies that depend on marine ecosystem services.

If global warming continues, excess heat and carbon dioxide trapped in the oceans may still take hundreds years to be re-emitted, even after greenhouse gas emissions are eventually reduced. According to United Nations Environment Programme (UNEP), economic sectors are likely to face difficulties related to climate change which include banks, agriculture, transport and others. Developing countries dependent upon agriculture will be particularly harmed by global warming.

The Global Humanitarian Forum projected in a 2009 report that in 2010, about 14,500 deaths due to droughts, temperature extremes, floods, storms, and wildfires will directly attributable to climate change, and 29,000 in 2050 if trends continue. 99% of those deaths are within developing countries. Likewise, in 2010, nearly 87 million people will be affected by those conditions, and 351 million in 2050 if current trends continue.

The world's primary international agreement on reducing greenhouse gas emissions is the Kyoto Protocol. The Protocol now covers more than 160 countries and over 55 percent of global greenhouse gas emissions. Only the United States and Kazakhstan have not ratified the treaty, with the United States historically being the world's largest emitter of greenhouse gases. The treaty expires in 2012. International talks began in May 2007 on a future treaty to succeed the current one. UN negotiations are now gathering pace.

The issue of climate change has sparked debate weighing the benefits of limiting industrial emissions of greenhouse gases against the costs that such changes would entail. There has been discussion in several countries about the cost and benefits of adopting alternative energy sources in order to reduce carbon emissions. Business-centered organizations, conservative commentators, and companies such as the Competitive Enterprise Institute and ExxonMobil have downplayed IPCC climate change scenarios, funded scientists who disagree with the scientific consensus, and provided their own projections of the economic cost of stricter controls. Likewise, environmental organizations and a number of public figures have emphasized the potential risks of climate change and promote the implementation of GHG emissions reduction measures. Some fossil fuel companies have scaled back their efforts in recent years, or called for policies to reduce global warming.

Another point of contention is the degree to which emerging economies such as India and China should be expected to constrain their emissions. According to recent reports, China's gross national CO₂ emissions may now exceed those of the U.S. China has contended that it has less of an obligation to reduce emissions since its per capita emissions are roughly one-fifth that of the United States. India, also exempt from Kyoto restrictions and another of the biggest sources of industrial emissions, has made similar assertions. The U.S. contends that if it must bear the cost of reducing emissions, then China should do the same.

Jasvinder Sharma published 8 Books, the latest, a collection of Essays from Penguin. Won Sahitya Akademy Award in 2005.

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Global Warming - New challenges before the World

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