BACKGROUND: Storms will dump heavier rain and more snow around the world as earth's climate continues to warm in the next 100 years, according to several leading computer models. A new study by scientists at the National Center for Atmospheric Research (NCAR) explains how and where warmer oceans and atmosphere will produce more intense precipitation. Such information could help communities better manage water resources and anticipate possible flooding.
ABOUT GLOBAL WARMING: Global warming refers to an average increase in the earth's temperature -- which has risen about 1 degree Fahrenheit over the past 100 years -- which in turn causes changes in climate. A warmer earth may lead to changes in rainfall patterns, and a rise in sea level, for example, as polar glaciers melt. Some of this rise is due to the greenhouse effect: certain gases in the atmosphere trap energy from the sun so that heat can't escape back into space. Without the greenhouse effect, the earth would be too cold for humans to survive, but if it becomes too strong, the earth could become much warmer than usual, causing problems for humans, plants and animals.
WHAT NCAR FOUND: Both the oceans and the atmosphere are warming as greenhouse gases build. Warmer sea surfaces boost evaporation, while warmer air holds more moisture. As this soggy air moves from the oceans to the land, it dumps extra rain per storm. The greatest increases will occur over land in the tropics because that is where water vapor most tends to increase, according to the NCAR study. However, extra moisture combined with changes in sea-level pressures and winds means that northwestern and northeastern North America, northern Europe, northern Asia, the east coast of Asia, and southwestern Australia will also experience heavier rain or snowfall.
WHAT CAUSES RAIN AND SNOW: Rain and snow are two forms of precipitation, along with sleet, hail, dew and fog. Rising warm air carries water vapor high into the sky, where it cools and condenses into water droplets. Some vapor freezes into tiny ice crystals, which can attract cooled water drops to form snowflakes. As snowflakes fall, they meet warmer air and melt into raindrops, unless temperatures are below freezing close to the ground: then we get snow.
The American Meteorological Society contributed to the information in the TV portion of this report.