More intense and frequent rainstorms and more frequent hot days and nights are among the weather extremes forecast for North America, according to an Iowa State University researcher who was one of the lead authors of a new government climate report released last week.
William Gutowski, professor of geological and atmospheric sciences, said additional weather extremes - such as heavy downpours, frequent heat waves, intense hurricanes and more areas affected by drought - are likely to occur.
Gutowski was a coordinating lead author of a key chapter for the report titled Weather and Climate Extremes in a Changing Climate. The U.S. Climate Change Science Program and the Subcommittee on Global Change Research produced the 164-page report. The scientific assessment provides the first comprehensive analysis of observed and projected changes in weather and climate extremes in North America and U.S. territories.
Gutowski's chapter dealt with the degree to which climate changes over the past century can be attributed to human causes, and what lies ahead.
"There is scientific evidence," according to the report, "that a warming world will be accompanied by changes in the intensity, duration, frequency and geographic extent of weather and climate extremes." The report also stated human-induced warming has "likely caused much of the average temperature increase in North America over the past 50 years and, consequently, changes in temperature extremes."
Gutowski said extensive climate models project the continued warming of North America. The phenomenon has direct implications for extreme weather. "Weather events that have been occurring roughly once every 20 years might, in certain parts of the country, occur every five years or so by the end of the century."
While Iowa's flooding woes coincided with the report's release, Gutowski said a single weather extreme cannot be blamed on the earth's warming.
"You can't look at any given event and say it definitely was caused by global warming," he said. "What you can say is the likelihood has increased because that heavy precipitation is more likely to occur in a warmer climate."
Work on the report began in earnest in 2006, said Gutowski, adding that the contributing scientists dealt with some "rather contentious issues," such as changes in hurricanes, as they wrote the analysis.
"There were some vigorous, frank discussions," Gutowski noted. "The report had three levels of review. It was probably more heavily peer-reviewed than any journal paper I've ever been part of."
Gutowski said people have many different viewpoints on global warming. However, even the most skeptical "have gone from a point where they used to just want to deny there was any warming going on to where they now admit there is some warming even if they won't attribute it to humans."
After Hurricane Katrina flooded New Orleans, Gutowski said he sensed a shift in public attitudes. "I think the impact of Katrina on people of the United States really brought home the point very dramatically that we are not invulnerable to weather and climate.
"A number of things have come together to where the contention now is not whether this is occurring or whether humans are doing it, but what are the real outcomes? What can we see happening in the future?"
Fourteen federal agencies and departments participate in the U.S. Climate Change Science Program, which produced the report. The Intergovernmental Panel on Climate Change (IPCC) previously evaluated extreme weather and climate events globally. However, this report is the first specific assessment for North America. Gutowski and fellow Iowa State climate researchers Gene Takle and Ray Arritt contributed to the IPCC, which shared the 2007 Nobel Peace Prize with former Vice President Al Gore.
NOTE - The National Oceanic and Atmospheric Administration news release about the report is at this link: http://www.noaanews.noaa.gov/stories2008/
20080619_climatereport.html
William Gutowski
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