Within the last 40 years, it has been recognized that human activity is slowly increasing the atmospheric concentration of several gases (primarily carbon dioxide) that contribute to the greenhouse effect , and during the past 30 years scientists have begun to consider the climatic consequences of an enhanced greenhouse effect. Despite the degree to which this topic has recently become politicized both nationally and internationally, the scientists who study this problem do so without preconceived notions or biases: they honestly seek the best possible answer to the scientific question of how the Earth's climate will respond to artificial changes in atmospheric composition.
The principal tools used to study the climate changes associated with an enhanced greenhouse are global climate models. While great progress has been made in understanding our climate using these models, they are known to have significant deficiencies and limitations. Given these deficiencies, scientists around the world have convened to reach a consensus on what is reasonable to conclude from global climate model simulations of the enhanced greenhouse effect. The consensus, which is monitored and published by the Intergovernmental Panel on Climate Change, is that global average surface air temperature will rise by about 0.2° C per decade (if the carbon dioxide concentration continues rising at its current rate), global sea level will rise by about 0.2 to 0.8 meters over the next 100 years, and precipitation will increase over the high latitudes. The near-surface warming is expected to be greater over continents than over oceans, and the extremes of temperature and precipitation may swing over a wider range increasing the likelihood of drought in continental areas. A more thorough discussion of the background for climate change and a description of the changes that scientists agree are virtually certain, very probable, probable and uncertain may be found in an article by Prof. Eric Barron of Penn State University.
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