en.wikipedia.org/wiki/Global_warming
Carbon dioxide during the last 400,000 years and the rapid rise since the Industrial Revolution; changes in the Earth's orbit around the Sun, known as Milankovitch cycles, are believed to be the pacemaker of the 100,000 year ice age cycle.
identifies increased levels of greenhouse gases due to human activity as the main influence. This attribution is clearest for the most recent 50 years, for which the most detailed data are available. Contrasting with this view, other hypotheses have been proposed to explain some of the observed increase in global temperatures, including: the warming is within the range of natural variation;
The monthly CO2 measurements display small seasonal oscillations in an overall yearly uptrend; each year's maximum is reached during the northern hemisphere's late spring, and declines during the northern hemisphere growing season as plants remove some CO2 from the atmosphere.
levels are expected to rise due to ongoing burning of fossil fuels and land-use change. The rate of rise will depend on uncertain economic, sociological, technological, natural developments, but may be ultimately limited by the availability of fossil fuels.
Feedbacks The effects of forcing agents on the climate are complicated by various feedback processes. One of the most pronounced feedback effects relates to the evaporation of water.
injected into the atmosphere causes a warming of the atmosphere and the earth's surface. The warming causes more water to be evaporated into the atmosphere. Since water vapor itself acts as a greenhouse gas, this causes still more warming;
in the atmosphere warms the Earth's surface and leads to melting of ice near the poles. 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. Feedback effects due to clouds are an area of ongoing research and debate. Seen from below, clouds absorb infrared radiation and so exert a warming effect. Seen from above, the same clouds reflect sunlight and so exert a cooling effect. Increased global water vapor concentration may or may not cause an increase in global average cloud cover. The net effect of clouds thus has not been well modeled.
They conclude that even with an enhanced climate sensitivity to solar forcing, most of the warming during the latest decades is attributable to the increases in greenhouse gases.
Curves of reconstructed temperature at two locations in Antarctica and a global record of variations in glacial ice volume. Today's date is on the left side of the graph Curves of reconstructed temperature at two locations in Antarctica and a global record of variations in glacial ice volume.
Two millennia of mean surface temperatures according to different reconstructions, each smoothed on a decadal scale. The unsmoothed, annual value for 2004 is also plotted for reference. Two millennia of mean surface temperatures according to different reconstructions, each smoothed on a decadal scale. The unsmoothed, annual value for 2004 is also plotted for reference.
Calculations of global warming prepared in or before 2001 from a range of climate models under the SRES A2 emissions scenario, which assumes no action is taken to reduce emissions.
The geographic distribution of surface warming during the 21st century calculated by the HadCM3 climate model if a business as usual scenario is assumed for economic growth and greenhouse gas emissions.
HadCM3 climate model if a business as usual scenario is assumed for economic growth and greenhouse gas emissions. These models are based on physical principles of fluid dynamics, radiative transfer, and other processes, with some simplifications being necessary because of limitations in computer power. These models predict that the net effect of adding greenhouse gases is to produce a warmer climate.
Global glacial mass balance in the last 50 years, reported to the WGMS and the NSIDC. The increased downward trend in the late 1980s is symptomatic of the increased rate and number of retreating glaciers.
While changes are expected for overall patterns, intensity, and frequencies, it is difficult to attribute specific events to global warming. Other expected effects include water scarcity, changes in mountain snowpack, adverse health effects from warmer temperatures, and the spread of disease.
North Atlantic since about 1970, correlated with increases of tropical sea surface temperatures. There are also suggestions of increased intense tropical cyclone activity in some other regions where concerns over data quality are greater. Multi-decadal variability and the quality of the tropical cyclone records prior to routine satellite observations in about 1970 complicate the detection of long-term trends in tropical cyclone activity.
Politics of global warming The scientific findings surrounding global warming have led to the involvement of politicians, energy industry funding of critics and skeptical politicians, participation by environmental groups, and active discussions by pundit and media personalities over the cause, effects, and mitigations. Governments have taken stances, often widely divergent at national and local levels.
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