Moreover, in an unprecedented string, every month between April 1997 and October 1998 established a new temperature record. In 1996, the IPCC projected that the average surface temperature of the Earth would rise another two to six degrees Fahrenheit by the year 2100, with continued increases thereafter, unless concerted measures are adopted to limit the emissions of greenhouse gases. The IPCC has predicted several probable consequences of future warming, including sea level rises of an additional six to 37 inches by the year 2100, and increased frequency and duration of many extreme weather events, such as heat waves and droughts. Heavy rains and flooding are also predicted to occur more frequently in many parts of the world, since higher temperatures lead to more rapid rates of evaporation and precipitation. In the United States, where the best data are available, an increased number of extreme rainfall events has already been observed.
Climate change is likely to have wide-ranging and mostly adverse effects on human health.
The greater frequency of heat waves is expected to raise mortality rates from heat stress, and to enlarge the potential ranges of many infectious diseases, for example, bringing malaria and dengue fever into the temperate zone, including parts of the United States. For the 50 percent to 70 percent of the human population living in coastal areas, rising sea levels and more frequent storm surges could have devastating effects, subjecting millions of people's homes to periodic flooding or permanent submergence. In many parts of the tropics such as Africa, where inhabitants are already prone to malnutrition and famine, harvests are projected to decline as a result of climate change. In some temperate and northern regions, agricultural production could increase, depending on how the expected proliferation of pests and weeds due to climate change balances out the fertilizing effects of increased carbon dioxide. Global warming also has the potential to transform many of the world's natural ecosystems over the next century, causing, for example, about one-third of the Earth's forested area to undergo major shifts in composition.