From Global to Regional Climate Change: Relative Knowns and Unknowns about Global Warming

Atmospheric concentrations of major greenhouse gases (CO 2 , CH 2 , N 2 O, and CFCs) have increased significantly in the last century, mainly due to anthropogenic activities such as fossil fuel burning, deforestation, agriculture, and chlorofluorocarbon production. It is estimated that a doubling of carbon dioxide concentrations would eventually raise average global temperatures by 2 to 5°C, higher than they have been over the last one hundred thousand years. If greenhouse gas concentrations continue to grow as they have in recent decades, the effective doubling of CO 2 would occur by about the year 2030. The full extent of climate change caused by that doubling would be realized several decades later. This rate of climate change would be faster than ever before, and continued greenhouse gas emissions would warm temperatures even more. There is a concensus about how global climate would change as a result of increased greenhouse gas concentrations: higher concentrations would likely lead to stratospheric cooling, increases in atmospheric temperature and precipitation, and rise in sea level. Much less is known about how regional climate would change. It is not known whether temperatures would rise in all parts of the globe. Although global precipitation would increase, there could be a reduction in rainfall in many regions. We are also uncertain about how climate variability and the frequency of extreme events would change. All of these uncertainties make it difficult to predict effects of climate change on a regional scale.