Title: Climate Change Over the Last 100 Years
Headings: 
Climate Change Over the Past 100 Years
Content: Since   the beginning of the century, precipitation in the United States has increased   by about 6 percent, while the frequency of intense precipitation events (heavy   downpours of more than two inches per day) has increased by 20 percent. Such   events can cause flooding, soil erosion, and even loss of life. In some   midcontinental areas, increased evaporation has led to drought because the   heavy rains fell elsewhere. There is also evidence that ecosystems are reacting to warming. Between   1981 and 1991, the length of the growing season in the northern high latitudes    (between 45 o and 70 o N) increased by a total of up to   twelve days, as documented by satellite imagery. Greening in spring and summer   occurred up to eight days earlier, and vegetation continued to photosynthesize   an estimated four days longer. Global mean sea level has risen 4 to 10 inches over the last 100 years,   mainly because water expands when heated. The melting of glaciers, which has   occurred worldwide over the last century, also contributes to the rise. Formerly frozen soils (permafrost) in the Alaskan and Siberian arctic have also   begun to melt, damaging both ecosystems and infrastructure. Melting and tundra   warming will also lead to decay of organic matter and the release of trapped   carbon and methane, creating an additional source of greenhouse gases.