Global warming is the rise in the average temperature of Earth’s atmosphere and oceans. Since the early 20th century, Average temperatures have climbed 1.4 degrees Fahrenheit (0.8 degree Celsius) around the world since 1880, with about two-thirds of the increase occurring since 1980, according to NASA’s Goddard Institute for Space Studies. The 20th century’s last two decades were the hottest in 400 years and possibly the warmest for several millennia
Global Warming is primarily caused by increasing concentrations of greenhouse gases produced by human activities such as the burning of fossil fuels and deforestation. The primary greenhouse gas responsible for global warming is carbon dioxide. The U.S. is responsible for 19.91% of the carbon dioxide emissions worldwide. Carbon dioxide takes 100 years to disperse in the atmosphere. Even if emissions are stopped today, we will still feel the effects for years to come.
Intergovernmental Panel on Climate Change (IPCC) climate model indicated that during the 21st century the global surface temperature is likely to rise a further 1.1 to 2.9 °C (2 to 5.2 °F) for their lowest emissions scenario and 2.4 to 6.4 °C (4.3 to 11.5 °F) for their highest.
The effects of an increase in global temperature include a rise in sea levels and a change in the amount and pattern of precipitation, as well a probable expansion of subtropical deserts. Global warming would be associated with the continuing retreat of glaciers, permafrost and sea ice; more frequent occurrence of extreme-weather events including heat waves, droughts and heavy rainfall, ocean acidification and species extinctions due to shifting temperature regimes. Effects significant to humans include the threat to food security from decreasing crop yields and the loss of habitat.
Sea levels have risen between 4-8 inches worldwide during the last century, and experts predict they could rise as much 2 feet in the next 100 years.
The Arctic is feeling the effects the most. Average temperatures in Alaska, western Canada, and eastern Russia have risen at twice the global average, according to the multinational Arctic Climate Impact Assessment report compiled between 2000 and 2004.
Glaciers and mountain snows are rapidly melting—for example, Montana’s Glacier National Park now has only 27 glaciers, versus 150 in 1910. In the Northern Hemisphere, thaws also come a week earlier in spring and freezes begin a week later.
Coral reefs, which are highly sensitive to small changes in water temperature, suffered the worst bleaching—or die-off in response to stress—ever recorded in 1998, with some areas seeing bleach rates of 70 percent. Experts expect these sorts of events to increase in frequency and intensity in the next 50 years as sea temperatures rise.
The World Health Organization blames 150,000 deaths per year on the effects of global warming including extreme weather, drought, heat waves, decreased food production and the increased spread of diseases like malaria.
At least 279 species of plants and animals are already responding to global warming, migrating north to escape rising temperatures.
Coral reefs are highly sensitive to small changes in water temperature. Scientists say if current CO2 emission trends continue, the world’s coral reefs could be virtually destroyed by 2050.
Proposed policy responses to global warming include mitigation by emissions reduction, adaptation to its effects, and possible future geoengineering.
Reducing the amount of future climate change is called mitigation of climate change. The IPCC defines mitigation as activities that reduce greenhouse gas (GHG) emissions, or enhance the capacity of carbon sinks to absorb GHGs from the atmosphere. Adaptation to climate change may be planned, either in reaction to or anticipation of climate change, or spontaneous, i.e., without government intervention. Adaptation also define as the ability of a system (human, natural or managed) to adjust to climate change (including climate variability and extremes) to moderate potential damages, to take advantage of opportunities, or to cope with consequences.
While Geoengineering is the deliberate modification of the climate, has been investigated as a possible response to global warming, e.g. by NASAand the Royal Society.
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Source : http://www.wikipedia.org