Still w/the Midwest heatwave: Climate Change? Yes or no?

Probably yes, the recent heat wave in the Midwest can be attributed to global warming, write Stefan Rahmstorf and Dim Coumou for RealClimate. They conclude their statistical discussion with: 

…let’s take the most simple case of a normal distribution that is shifted towards the warm end by a given amount – say one standard deviation. Then, a moderately extreme temperature that is 2 standard deviations above the mean becomes 4.5 times more likely […]. But a seriously extreme temperature, that is 5 standard deviations above the mean, becomes 90 times more likely! Thus: the same amount of global warming boosts the probability of really extreme events, like the recent US heat wave, far more than it boosts more moderate events. 

And they include a couple of telling graphs, including this one from the most recent IPCC report: 


But no, argues Marty Hoerling, for NOAA:

A black swan most probably was observed in March 2012 (lest we forget 1910). Gifted thereby to a wonderful late winter of unprecedented balmy weather, we also now know that all swans are not white. The event reminds us that there is no reason to believe that the hottest, "meteorological maddest" March observed in a mere century of observations is the hottest possible. But this isn't to push all the blame upon randomness. Our current estimate of the impact of GHG forcing is that it likely contributed on the order of 5% to 10% of the magnitude of the heat wave during 12-23 March. And the probability of heatwaves is growing as GHG-induced warming continues to progress. But there is always the randomness.

And Hoerling has an example to point to, in which conditions in models in February led to a record predicted heat wave:

The key feature of the evolving predictions is a sudden and abrupt emergence of a very warm March prediction for the Upper Midwest/Ohio Valley region in the February initialized forecasts. These are substantial changes statistically because each plot represents a 40-run average. Prior forecasts had anticipated warm conditions mostly along the southern tier of the U.S., consistent with the impact of ongoing cold tropical Pacific SSTs associated with a La Nina event.

It's puzzling to me that Hoerling should be able to see an extreme heat wave in model runs from February, but still doubt that a black swan event could be attributed to climate change.

I'm missing something, I guess. 

Published by Kit Stolz

I'm a freelance reporter and writer based in Ventura County.

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