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21st Century Climate Change

Prediction of climate change over the next 100 to 150 years is based solely on climate model simulations run on computers. The vast majority of modelling has concentrated on the effects of continued man-made pollution of the atmosphere by greenhouse gases, and to a lesser extent, atmospheric aerosols. The main concern at present is to determine how much the Earth will warm in the near future.

Significant results from some of the best climate models available indicate that a global average warming of 0.3C per decade can be expected to occur during the 21st century, assuming that mankind fails to control current emissions of greenhouse gases, although it could be as high as 0.6C. In addition regional variations in the patterns of temperature and precipitation change will occur, with greater warming likely in the polar regions. Currently, models suggest that if the atmospheric concentration of carbon dioxide, the main greenhouse gas, is doubled from pre-industrial levels, the Earth will warm by between 1.5 and 4.5C sometime over the next 200 years or so. The large margin of error in future prediction of temperature emphasises that modelling the climate is inherently a difficult business. Part of the problem stems from trying to guess what climate feedbacks might occur that may enhance the initial warming due to an enhanced greenhouse effect. Melting ice in the polar regions for example could accelerate warming because exposed ground absorbs more energy from the Sun than snow and ice, which reflect about 80 to 90%.

Whilst uncertainties concerning the actual response of the global climate to man-made greenhouse gas emissions exist, most scientists agree that the global warming trend of the 20th century will continue into the 21st century. The projected rate of warming is faster than at any time during recent Earth history. If nations fail to respond, the world may experience numerous adverse impacts as a result of global warming in the decades ahead.