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Global warming

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Jump to: navigation , search For past climate change , see paleoclimatology and geologic temperature record .

Global mean surface temperature anomaly relative to 19611990

Mean surface temperature anomalies during the period 1999 to 2008 with respect to theaverage temperatures from 1940 to 1980

Global warming is the increase in the average temperature of the Earth's near-surface airand oceans since the mid-twentieth century and its projected continuation. Global surfacetemperature increased 0.74 0.18 C (1.33 0.32 F) during the last century. [1]A[] TheIntergovernmental Panel on Climate Change (IPCC) concludes that anthropogenic greenhouse gases are responsible for most of the observed temperature increase since themiddle of the twentieth century, [1] and that natural phenomena such as solar variation andvolcanoes probably had a small warming effect from pre-industrial times to 1950 and asmall cooling effect afterward. [2][3] These basic conclusions have been endorsed by more

than 40 scientific societies and academies of science ,B[]

including all of the nationalacademies of science of the major industrialized countries .[4]

Climate model projections summarized in the latest IPCC report indicate that globalsurface temperature will probably rise a further 1.1 to 6.4 C (2.0 to 11.5 F) during thetwenty-first century. [1] The uncertainty in this estimate arises from the use of models withdiffering climate sensitivity , and the use of differing estimates of future greenhouse gasemissions . Some other uncertainties include how warming and related changes will varyfrom region to region around the globe. Most studies focus on the period up to 2100.However, warming is expected to continue beyond 2100 even if emissions stop, becauseof the large heat capacity of the oceans and the long lifetime of carbon dioxide in the

atmosphere.[5][6]

Increasing global temperature will cause sea levels to rise and will change the amountand pattern of precipitation , probably including expansion of subtropical deserts .[7] Thecontinuing retreat of glaciers , permafrost and sea ice is expected, with the Arctic region being particularly affected. Other likely effects include shrinkage of the Amazonrainforest and Boreal forests , increases in the intensity of extreme weather events, speciesextinctions and changes in agricultural yields .

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Political and public debate continues regarding the appropriate response to globalwarming. The available options are mitigation to reduce further emissions; adaptation toreduce the damage caused by warming; and, more speculatively, geoengineering toreverse global warming. Most national governments have signed and ratified the KyotoProtocol aimed at reducing greenhouse gas emissions.

Question: What Causes Global Warming?

Answer: Scientists have determined that a number of human activities are contributing toglobal warming by adding excessive amounts of greenhouse gases to the atmosphere.Greenhouse gases such as carbon dioxide accummulate in the atmosphere and trap heat thatnormally would exit into outer space.

Greenhouse Gases and Global Warming While many greenhouse gases occur naturally and are needed to create the greenhouse effect

that keeps the Earth warm enough to support life, human use of fossil fuels is the main sourceof excess greenhouse gases . By driving cars, using electricity from coal-fired power plants, orheating our homes with oil or natural gas, we release carbon dioxide and other heat-trappinggases into the atmosphere. Deforestation is another significant source of greenhouse gases,because fewer trees means less carbon dioxide conversion to oxygen.

During the 150 years of the industrial age, the atmospheric concentration of carbon dioxidehas increased by 31 percent. Over the same period, the level of atmospheric methane hasrisen by 151 percent, mostly from agricultural activities such as raising cattle and growingrice.

Effects of global warmingThere are two major effects of global warming:

Increase of temperature on the earth by about 3 to 5 C (34 to 41 Fahrenheit)by the year 2100.

Rise of sea levels by at least 25 meters (82 feet) by the year 2100.

More details about the effects of global warming :

Increasing global temperatures are causing a broad range of changes. Sea levels are

rising due to thermal expansion of the ocean, in addition to melting of land ice. Amounts

and patterns of precipitation are changing. The total annual power of hurricanes has

already increased markedly since 1975 because their average intensity and average

duration have increased (in addition, there has been a high correlation of hurricane power

with tropical sea-surface temperature).

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Changes in temperature and precipitation patterns increase the frequency, duration, and

intensity of other extreme weather events, such as floods, droughts, heat waves, and

tornadoes. Other effects of global warming include higher or lower agricultural yields,

further glacial retreat, reduced summer stream flows, species extinctions. As a further

effect of global warming, diseases like malaria are returning into areas where they have

been extinguished earlier.

Although global warming is affecting the number and magnitude of these events, it is

difficult to connect specific events to global warming. Although most studies focus on the

period up to 2100, warming is expected to continue past then because carbon dioxide

(chemical symbol CO 2) has an estimated atmospheric lifetime of 50 to 200 years.