Global warming to bring heavier rains, snow

Rising temperatures in the world's atmosphere and oceans will lead to more intense storms as the century progresses, according to a new report from the National Center for Atmospheric Research.

Evaporation increases when the surface temperature of the ocean rises and warmer air can hold more moisture. When this soggier-than-normal air moves over land, it results in storms wetter and more intense than those experienced in the past.

The greatest changes will occur over land in the tropics, according to the study, which was released Thursday. Heavier rain or snow, however, will also fall in northwestern and northeastern North America, northern Europe, northern and eastern Asia, southwestern Australia, and parts of South America during the current century.

"The models show most areas around the world will experience more intense precipitation for a given storm during this century," lead author Gerald Meehl said in a statement. "Information on which areas will be most affected could help communities to better manage water resources and anticipate possible flooding."

The Mediterranean and the southwestern U.S., meanwhile, will experience a different pattern. Storms will likely become wetter, particularly in the fall and winter, but dry spells may stretch for longer in the warmer months. A picture of how this pattern might develop was seen in Europe this year: While Germany endured unprecedented floods, Spain and Portugal imposed water rationing because of a lengthy drought.

Researchers at the Massachusetts Institute of Technology in April released a report predicting that hurricanes would become more intense over the coming century. It became an oft-cited study after Hurricane Katrina hit.

Climate change has become a hot-button issue for scientists, politicians and the general public. The scientific community now generally agrees that global warming is in fact happening, and most of the future scenarios aren't pretty.

Rising sea levels could lead to more frequent flooding in Bangladesh and other low-lying nations. Food production could also be disrupted. Melting polar ice is expected by some to lead to a sea lane above Siberia in a few years.

While scientists generally agree that the world's climate is changing, there is more disagreement over how much of the change is due to human behavior. Some believe a great deal of the warming is caused by burning fossil fuels, which create greenhouse gases that trap heat. Examination of data from the 20th century implicates humans, Meehl said in a phone interview.

"Probably most of the climate change in the early part of the century was caused by natural events," he said, such as a rebounding of temperatures that ordinarily occurs after volcanoes. "But the change in the latter part of he 20th century was the result of human activity."

Others disagree. Still others assert that, because the stakes are so high, debating whether or not reducing greenhouse gas emissions can help makes no sense.