Temperature changes of the magnitude expected from the enhanced greenhouse effect have occurred in the past, but the previous changes took place over centuries or millennia instead of decades. Rates of natural migration and adaptation of species and communities appear to be much slower than the predicted rate of climate change. As a result, populations of many species and inhabited ranges could change as the climate to which they are adapted effectively shifts northward or to higher elevations. One of the consequences of global climate change may be increases in the frequency of extreme weather events, particularly droughts and floods. These events, when they do occur, can be costly.
Floods are more likely because the frequency of intense rainfall is predicted to increase.
Water scarcity in Middle Eastern and African countries is also likely to be exacerbated by climate change. A 50 cm rise in sea level by the year 2100, which is within the range projected by the IPCC, could inundate more than 5,000 mi2 of dryland and an additional 4000 mi2 of wetlands in the U.S. if no protective actions are taken. Internationally, many low- lying areas such as parts of the Maldives, Egypt, and Bangladesh would be completely inundated and uninhabitable by a similar sea level rise. Changing temperatures and precipitation patterns may produce new breeding sites for pests and pathogens. Drought could become more frequent, particularly in the Great Plains.