InsideClimate News reports: When Michael Mann goes before Congress Wednesday to testify on global warming, he’ll be armed with one more piece of evidence that greenhouse gases from fossil fuel burning are fundamentally altering the climate and leading to life-threatening and costly extreme weather.

Mann is the lead author of a new study showing that the greenhouse gas buildup is slowing down planetary atmospheric waves, which results in regional summer climate extremes. That includes a deadly 2003 European heat wave, as well as extensive wildfires in Siberia and severe flooding in Pakistan that took place simultaneously in 2010.

Pennsylvania State University climate scientist Mann said he and his fellow scientists discovered, by studying extensive climate data, “a particular type of jet stream pattern that is associated with many of the extreme events we’ve seen in recent years.” He added that there is every reason to expect “these persistent weather events to become more prominent over time…with increasing greenhouse gas concentrations.”

Mann is a high-profile scientist whose advocacy of climate action has made him a lightning rod for criticism from the right. He will testify Wednesday before the House Science, Space and Technology Committee, led by Texas Republican Lamar Smith, in a hearing that is stacked with climate change skeptics.

The study, published March 27 in the journal Scientific Reports, examines temperature data related to the jet stream and winds that flow around the Northern Hemisphere from west to east and that loop from north to south between the tropics and the Arctic. The pattern is called Rossby waves.

“We identified particular temperature patterns that occur when these large planetary waves slow down, and we found that, in the course of the past 100 years, this pattern is becoming more frequent,” said study co-author Stefan Rahmstorf, a scientist with the Potsdam Institute for Climate Impact Research. [Continue reading…]