Extreme Wet
The atmosphere's water-holding capacity increases by about 4 percent for every 1° Fahrenheit (0.6° Celsius) rise in temperature. This effect is similar to the difference between a warm bathroom and a cold bathroom: the mirror fogs up more when the air is warmer.
Extreme precipitation is likely when a storm passes through a warmer atmosphere holding more water. In warmer months, it takes the form of torrential rainstorms; in winter,blizzards are more likely.
At the same time, most regions, in the face of warming temperatures, are losing snow cover on the ground that lasts longer than 30 days. Winters are shorter, fewer cold records are set, more precipitation is falling as rain and less as snow—although whopper snowstorms are even more likely in some places—and snowpacks are shrinking and melting earlier. Whether precipitation falls as rain or snow, these extremes can heighten the risk of flood, and cause economic and social disruptions for communities unprepared to cope.
Wet places tend to get wetter. Atmospheric circulation over oceans, plains, and mountains helps determine where rainforests thrive and semi-arid regions develop. However, wet places tend to get wetter and dry places dryer in a warming world—as is already occurring today. Places now wetter than the historical average include Northern Europe, eastern North and South America, and northern and central Asia. Northern Scandinavia and South and North Korea recorded precipitation increases of 3-15 percent per decade between 1979 and 2005. In the U.S. Northeast, the number of days with very heavy precipitation rose by 58 percent over the last 50 years, while the number of such days in the U.S. Midwest rose 27 percent. Yet even as rainfall occurs in heavier events, the periods between these extremes are likely to become longer, warmer, and drier. Scientists expect these trends to intensify if our carbon emissions continue unabated.
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