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Posted at 04:21 PM ET, 07/05/2012

Did global warming intensify the derecho in Washington, D.C.?


Infrared satellite image of derecho over Washington, D.C. (CIMMS Satellite blog)
The June 29 derecho, which caused widespread damage in Washington, D.C. blossomed to full fury in a record hot environment. Could the heat added to the atmosphere from manmade greenhouse gases have provided extra fuel to this explosive storm?

The amount of energy available to this storm was extreme and, wundergound weather historian Chris Burt called the number of all-time heat records set around the time “especially extraordinary.”

But as I wrote the day after the storm, connecting global warming to the derecho is a complicated and controversial question.

Complicated?

I posed the question to Harold Brooks, a researcher at NOAA’s National Severe Storms Laboratory and an expert on climate change and severe storms.

He won’t rule out any role, but said he doesn’t think it’s “significant”. The main complication in answering the question, he says, is that we don’t know how much greenhouse gases contributed to the heat wave and to the amount of instability in the atmosphere.

Satellite loop of derecho moving from west of Chicago through Washington, D.C. Courtesy CIMSS Satellite blog.

Brooks also stressed the importance of the harmonious configuration of the winds in the lower atmosphere relative to storm’s straight ahead motion - a critical feature of derechos not meaningfully impacted by global warming.

For the more technically inclined, here’s his direct response to the question [was there a climate warming role in the derecho?]:

“Not to a particularly significant extent. The hot surface temperatures and high lapse rates aloft directly contributed. I’m not sure how much of either of those goes to long-term warming trends. An important aspect was the set up of the vertical wind profile in relationship to storm motion.”

Controversial?

Meteorologist and blogger Anthony Watts, cringed at the mere question of a global warming link. Watts argued derechos are nothing new. He pointed out these storms were occurring in the late 1800s when the term derecho was coined. Further, he noted, NOAA’s Storm Prediction Center has an entire website devoted to derecho history.

He implies, before even asking the question, I should’ve considered derecho history:

...Samenow cites the same sources from the Storm Prediction Center page that I do ... Yet somehow, he managed to conveniently ignore the historical context and the climatological frequency of derechoes on that page.

But Watts’ argument is incomplete and unconvincing. He’s asserting that question shouldn’t be asked on the basis of an anecdotal list of past derechos which NOAA confesses is incomplete. To objectively demonstrate global warming has no role in derecho behavior, it would require analysis of a complete record of derecho frequency and intensity which doesn’t exist. Watts’ insinuation that the mere existence of derechos in the past means we shouldn’t even ponder a possible global warming role is flawed.

The reality seems to be observations and scientific tools necessary to determine any global warming role in the June 29 derecho are either non-existent or limited. But that doesn’t mean we shouldn’t consider the question or attempt to unravel this complex issue.

While we lack observed data, theory suggests violent non-tornadic thunderstorm winds are likely to increase in a warmer world, says SPC’s Brooks. He told me the following:

“I think it’s quite plausible that we’d expect more non-tornadic wind events in a warmer climate. For starters, in the US, most of the high wind events are in late June-August [when it’s warmest], so climatology tells us that’s when they occur. Whether they occur in the organized fashion of derechos or in less organized storms is a difficult question to answer.”

Related: Are La Nina and global warming behind the extreme tornado activity?

By  |  04:21 PM ET, 07/05/2012

Categories:  Latest, Climate Change, Thunderstorms

 
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