The report said, however, that climate change likely led to an increase in heavy precipitation events and the amount of precipitation.
Pielke said that floods in the United State have not increased in intensity or frequency since at least 1950 and that hurricane landfalls in the country have not increased in frequency, intensity or normalized damage since at least 1900.
The federal government's Storm Prediction Center, based in Norman, says the effect of climate change on tornado occurrence is unknown.
“Climate models cannot resolve tornadoes or individual thunderstorms,” the center says on its webpage. “They can indicate broad-scale shifts in three of the four favorable ingredients for severe thunderstorms (moisture, instability and wind shear), but as any severe weather forecaster can attest, having some favorable factors in place doesn't guarantee tornadoes.”
Rep. Suzanne Bonamici, D-Ore., said Wednesday that lawmakers should be focusing on the cumulative effects of climate change.
“To focus only on the question of whether there will be more extreme events misses the point that by the end of this century, much of the world as we know it ... will be considerably altered by the weather effects of climate change,” she said.
Pielke said the fact storms and droughts couldn't be attributed to climate change didn't mean human-caused climate change wasn't real.
“It does mean, however, that some activists, politicians, journalists, corporate and government agency representatives and even scientists who should know better have made claims that are unsupportable based on evidence and research,” he said.