Texas-sized drought of 2012: Fluke or global warming?

The extreme drought of 2012, which persists into 2013 in about half the country, was just a fluke, says a massive report by dozens of government scientists, helmed by Martin Hoerling. Hoerling is an expert in general circulation models and projections, specializing in the Southwest, and a believer in global warming.

As Seth Borenstein wrote for the AP:

Last year's huge drought was a freak of nature that wasn't caused by man-made global warming, a new federal science study finds.

Scientists say the lack of moisture usually pushed up from the Gulf of Mexico was the main reason for the drought in the nation's midsection.

Thursday's report by dozens of scientists from five different federal agencies looked into why forecasters didn't see the drought coming. The researchers concluded that it was so unusual and unpredictable that it couldn't have been forecast.

"This is one of those events that comes along once every couple hundreds of years," said lead author Martin Hoerling, a research meteorologist at the National Oceanic and Atmospheric Administration. "Climate change was not a significant part, if any, of the event."

But Kevin Trenberth, who has published more than 400 papers on climate, and is a leader at the National Center for Atmospheric, criticized the report for narrow-mindedness. From Andrew Freedman's story at Climate Central: 

Kevin Trenberth, a researcher at the National Center for Atmospheric Research and a frequent critic of Hoerling's work, blasted the report's conclusions in an online commentary. "The question never addressed is what does global warming and human influences bring" to the High Pressure areas typically associated with extreme heat and drought events, Trenberth said. 

The report, Trenberth said, "fails completely to say anything about the observed soil moisture conditions, snow cover, and snow pack during the winter prior to the event in spite of the fact that snow pack was at record low levels in the winter and spring."

Trenberth has a least one point I can speak to, and bring in the work of John Neilsen-Gammon of Texas A&M, the state climatologist of Texas, to verify. I saw a big presentation he gave at the American Meteorological Society on the drought that struck Texas last year (and which has persisted into 2013 in much of the state). 

Neilsen-Gammon said that about 20% of the drought could be attributed to global warming, which indirectly tends to support Trenberth's view. But more directly, Neilsen-Gammon said that they knew in Texas in the fall of 2011 that Texas would go into drought in 2012 because the ground was so dry that there would not be enough moisture in the air to make possible a significant amount of rain. That's what Trenberth alluded to in one of his points. 

What caused this dryness? Well, might not record-breaking heat have something to do with it? And might not record breaking heat waves have some connection to global warming? 

But Hoerling et al certainly looked at soil moisure, and the lack thereof in Texas can clearly be seen in some of their own slides (from the report, which looks unusually clear and well presented). 

Slide-17-1024
So I must read this report, first. For myself and perhaps for some of you. 

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