Reported February 2006

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, causing changes in climate. The earth's temperature has risen about 1 degree F over the past 100 years. A warmer earth may lead to changes in rainfall patterns and a rise in sea level. An example of this is when polar glaciers melt. Some of this rise in temperature 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. Extra moisture combined with changes in sea-level pressures and winds, however, means 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.

If you would like more information, please contact:

University Corporation for Atmospheric Research
1850 Table Mesa Dr.
Boulder, CO 80305
(303) 497-1174

For more information on meteorological science, contact:

The American Meteorological Society
45 Beacon Street
Boston, MA 02108-3693
(617) 227-2425
http://www.ametsoc.org

FACTOID...

Raindrops are actually shaped like hamburgers. But as they fall, the air pushes on the bottoms of the drops, causing them to flatten out while the tops remain round, producing a teardrop shape.

ON THE WEB:

For kids: http://www.epa.gov/globalwarming
For adults: http://yosemite.epa.gov/oar

NCAR: http://www.ucar.edu