June 19 (Bloomberg) -- The chances for extreme weather in the U.S. such as the record rainfall and flooding in Iowa this month are increasing as worldwide temperatures rise, a government agency that researches climate change said.

North America may get more abnormally hot days and nights, heavier downpours and deadlier storms from global warming, today's report from the Bush administration's U.S. Climate Change Science Program said. Elevated temperatures in recent decades already have led to more intense rainstorms in the Midwest, Northeast and Mid-Atlantic regions, said Thomas Karl, co-chairman of the report.

``The probability of heavy downpours is increasing, which leads to events like what we're seeing in the Midwest,'' said Karl, director of the National Climatic Data Center at the National Oceanic and Atmospheric Administration, in an interview.

The Iowa disaster helped drive corn prices to a record high. Flood damage may exceed $2.7 billion, according to economics professors Mark Burton at the University of Tennessee in Knoxville and Michael Hicks at Ball State University in Muncie, Indiana.

``We think that climate change is really a driver, not only in tropical storms but in other precipitation events,'' Eberhard Faust, head of climate risk analysis for Munich Re, the world's second-biggest re-insurer, said in an interview before the report. ``We can anticipate that many of these processes will get even worse, even stronger.''

Billion-Dollar Disaters

From 1980 to 2006, there have been 70 weather-related U.S. disasters that each caused more than $1 billion in damage, the study said. Continued warming, which scientists have blamed largely on a greenhouse effect stemming from carbon-dioxide emissions and deforestation, may also lead to more frequent droughts, it concluded.

``There are aspects of it that certainly imply that the costs are going to go up,'' Thomas Peterson, a NOAA scientist and co-author of the report, said on a conference call with reporters.

Some measures designed to protect against moderate weather events can backfire, the report said. For example, when levees that allow housing and other development in floodplains fail during extreme weather, more people and buildings are at risk.

Eleven levees on the 96-mile stretch of the Mississippi River from Hannibal, Missouri, to St. Louis have overtopped and four more are in danger of failing from this week's flooding, the Army Corps of Engineers said.

Frequent Flooding

Today's report didn't specifically mention the Iowa floods. Karl, when asked about Iowa, said, ``Those types of events will increase in frequency as time goes on and global temperatures increase.''

The climate program was created by President George W. Bush in 2002 to integrate research from federal agencies, including the Energy Department and the National Aeronautics & Space Administration. Last month, the agency reported that burning fossil fuels in power plants and automobiles is most likely responsible for global warming, endorsing an opinion accepted by many of the world's scientists.

``Human-induced warming is known to affect climate variables such as temperature and precipitation,'' according to the report. ``Within a changing climate system, some of what are now considered to be extreme events will occur more frequently.''

Carbon dioxide, a byproduct of burning coal, oil, and natural gas, contributed most to global warming in the last century, the climate program said. Greenhouse gases cause the atmosphere to hold more water vapor, leading to heavy downpours, and sea surface temperatures to rise, which produces stronger hurricanes.

Iowa Evacuations

Flooding and severe weather have killed at least 24 people in Iowa, Wisconsin and Kansas this month and forced the evacuation of more than 40,000 people. In the past two weeks, parts of Iowa received as much as 15 inches (38.1 centimeters) of rain, more than double the normal amount, National Weather Service data show.

``Precipitation is likely to be less frequent but more intense,'' according to today's report. Daily rainfall ``so heavy that it now occurs only once every 20 years is projected to occur approximately every eight years by the end of this century.''

By the middle of the century, a day so hot that it now occurs once every 20 years will occur every three years over much of the continental U.S. and every five years over most of Canada, according to the report. North Atlantic and North Pacific hurricanes will pack stronger winds, more rainfall and higher storm surges.

``Its likely that future hurricanes will have stronger winds and in particular will have much more intense precipitation,'' Gerry Meehl, senior scientist at the National Center for Atmospheric Research, said.

To contact the reporter on this story: Jim Efstathiou Jr. in New York at jefstathiou@bloomberg.net.

Last Updated: June 19, 2008 15:17 EDT