WASHINGTON -- If you think the weather is getting more extreme, you're right — and global warming caused by human activity probably is the reason, according to a report released Thursday by a panel of government scientists.
The report comes as the Midwest copes with record rainfall and catastrophic flooding.
There is strong evidence the increasing frequency of extreme rain, heat, drought and tropical storms is caused by global climate change, according to the report from the U.S. Climate Change Science Program.
"Changes in some weather and climate extremes are attributable to human-induced emissions of greenhouse gases," the study authors concluded.
The report is a synthesis of the latest research on extreme weather in the U.S. and comes after nearly six months that saw a record number of tornadoes, unusual winter warmth and record-setting precipitation in many regions.
The most extreme weather event so far this year, the Midwest floods, continues to unfold.
Climate change likely played an important role in setting up conditions that led to the region's second 500-year flood event in 15 years, according to experts.
As global temperatures have increased in recent years, so have sea surface temperatures. Warmer oceans evaporate more water vapor into the atmosphere. Water vapor is the fuel that drives rainstorms.
"When you get a system like we have had over the past month or two in the Midwest, this persistent pattern of low pressure and fronts in the area, now there is more moisture to work with and they produce frequently heavy rains," said Ken Kunkel, interim chief of the Illinois State Water Survey office and one of the authors of the report released Thursday.
It's the opposite of the severe drought that helped create the Dust Bowl of the 1930s that caused extensive environmental and agricultural damage.
"The data are quite clear," said Kunkel, who specializes in studying U.S. extreme precipitation. "We're in an era when these heavy rain events have been occurring more frequently."
The report also concluded that:
• Human-caused warming likely has caused much of the increase in average and extreme temperatures observed in the U.S. over the past 50 years.
• Heavy precipitation events have increased over the past 50 years. That's consistent with increases in atmospheric water vapor associated with human-caused increases in greenhouse gases.
• Droughts are becoming more severe in some regions, though there are no clear national trends.
• The power and frequency of Atlantic hurricanes have increased substantially in recent decades, likely driven by human-caused increases in sea surface temperatures. However, the number of hurricanes making landfall does not appear to have increased over the past century.