Scientists (once again) "stunned" by heatwave

Late-September heat wave leaves climate experts stunned

"Never been a heat wave of this duration and magnitude this late in the season," reports NOAA

Joe Romm

Think Progress,

27 September, 2017

Century-old records across the Midwest and East Coast are being shattered by a monster late-September heat wave — the kind of extreme weather we can expect to get much worse thanks to President Donald Trump’s policies to undermine domestic and global climate action.

“There has never been a heat wave of this duration and magnitude this late in the season in Chicago,” the National Weather Service reported Tuesday evening.

From Wednesday through Tuesday, for example, Chicago sweltered through “the only occurrence on record of 7+ consecutive 90°[F] days entirely within September.” Every day of the heatwave was 92°F or above, and every one set a new record high for that date.

“Summer in some regions of the world will become one long heatwave even if global average temperatures rise only 2°C [3.6ºF] above pre-industrial levels,” finds a study published Monday in Nature Scientific Reports. The Paris climate agreement, which Trump has decided to pull out of, seeks to limit global warming to “well below” 3.6ºF.

On Wednesday, another study showed the connection between deadly heat waves and climate change. Scientists with World Weather Attribution (WWA) released an analysis of Europe’s blistering summer heat, which included the heat wave so deadly it was nicknamed “Lucifer.” The researchers found, “climate change increased the chances of seeing a summer as hot as 2017 by at least a factor of 10 and a heat wave like Lucifer by at least a factor of four since 1900″ (emphasis in original).

Back in the United States, the current heat wave has set records across the Midwest and East. On Monday, 92ºF was the hottest Burlington, Vermont had ever been that late in the year — by a full seven degrees, the Washington Postreported. On Sunday and Monday, Buffalo, New York saw its latest-ever consecutive 90ºF days. Records for hottest day or hottest series of days this late in the year were crushed in Minneapolis; northern Maine; Ottawa, Canada; and Green Bay, Wisconsin.

“It’s perhaps obvious that global warming means more frequent and intense heat waves,” climatologist Michael Mann noted in an email to ThinkProgress. “But what is less obvious is how climate change may be impacting the behavior of the jet stream in way that causes more persistent weather extremes, giving us even more extreme and longer-duration heat waves than we would otherwise expect.”

The National Weather Service tweeted out a chart showing this very effect.

The scientific evidence and analysis is getting stronger and stronger that carbon pollution is changing the jet stream in ways that cause high pressure ridges that block or stall weather patterns. A similar effect stalled Superstorm Harvey over Houston, leading to a once-in-25,000-year deluge.

“Many of the worst heat waves in recent history, including the 2003 European heat wave and the 2011 Texas/Oklahoma heat wave, were associated with this effect,” Mann said.

The latest science makes it very clear that stronger heat waves are becoming far more likely, thanks to global warming — and that the warmer it gets the worse the heat waves will get.

Indeed, the new Nature Scientific Reports study finds that for each additional 1.8°F of global warming during the summer, there would likely be:

• 15 to 28 more heat wave days each year
• Heat waves would last 3 to 18 days longer
• The peak intensity of heatwaves will increase 2.2°F to 3.4°F

But while the rest of the world is working to limit additional warming as much as possible, Trump’s policies would take us to upwards of 5.4°F or more additional warming. In the worst case, we can see as many as 80 more heat wave days, heat waves could be 50 days longer, and the peak intensity could be as much as 10°F higher than it is now.