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Extreme Weather: What’s Climate Change Got to Do With It?


by Bill Chameides | April 19th, 2013
posted by Erica Rowell (Editor)

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A devastating drought gripped a large swath of the United States in 2012, decimating corn crops like those pictured here in Missouri Valley, Iowa, in August. Just what is behind the long-lasting drought is the subject of scientific debate. 
(Photo: USDA/Dave Kosling)
A devastating drought gripped a large swath of the United States in 2012, decimating corn crops like those pictured here in Missouri Valley, Iowa, in August. Just what is behind the long-lasting drought is the subject of scientific debate. (Photo:
USDA/Dave Kosling)

A debate brews on the role of climate change in the record-breaking drought of 2012.

Remember all the weather drama in the Midwest last year? A record-breaking drought [pdf] that eclipsed the Dust Bowl days of the 1930s gripped the heartland and spread from there. By year’s end, more than 70 percent of the contiguous United States was abnormally dry or worse. The heat and dryness decimated the U.S. corn crop, led to disastrous wildfires in the West, and even came close to bringing shipping on the Mississippi River to a grinding halt because of low water levels.

Funny thing is (actually not funny at all), it was just a year prior that the worst flooding since 1925 occurred along the Mississippi. Talk about huge swings.

That Was Last Year. What’s With the Midwest This Year? 

Currently, more than 60 percent of the contiguous United States is abnormally dry or worse. But while much of the Mountain and western states are predicted to remain in the grips of the drought, there appears to be some good news for the Midwest (see graphic). NOAA’s most recent drought prediction, released on April 18, has much of the Midwest seeing some relief from drought from now through the end of July.

The problem is that that predicted relief may be more than the Midwesterners bargained for.

The region has been hit by a spate of intense storms, the latest of which was a massive system stretching from Texas to Michigan bringing snow, rain and high winds to the region. Illinois has declared a weather-related state of emergency as flash floods hit Chicago particularly hard after seven inches of rain fell in 24 hours beginning on Wednesday night. Numerous towns and cities along the Mississippi River and its tributaries are either flooded or preparing for flooding.

And so what had been just a few months ago a Mississippi River so low that shipping was problematic is now a river that will likely flow over its banks causing widespread flooding this spring.

(Source: NOAA)

So what’s going on?

Can all this weather be lumped together as the climate’s natural variability? Or is it a sign of the “new normal” — the normal after the effects of anthropogenic climate change have done their thing?

NOAA Scientists Weigh In: It’s Natural Variability

A March report by the National Oceanic and Atmospheric Administration on the causes of the 2012 drought by Martin Hoerling of NOAA’s Earth Systems Research Laboratory and coauthors has gotten a good deal of play in the media. The report concludes that the drought of 2012 cannot be attributed to climate change, stating that the “central Great Plains drought during May-August of 2012 resulted mostly from natural variations in weather.”

With regard to the specific cause of the drought, the report concludes [pdf] that:

  • “Moist Gulf of Mexico air failed to stream northward in late spring ….
  • Summertime thunderstorms were infrequent and when they did occur produced little rainfall.
  • Neither ocean states nor human-induced climate change … appeared to play signifi­cant roles in causing severe rainfall defi­cits over the major corn producing regions of central Great Plains.”

I’m a bit nonplussed about the first two points. Yep, it was dry in the Midwest and there was little rainfall and so there was a drought. Do you need to be a climate scientist to conclude that? We all get that, but why?

The third conclusion rules out climate change as the answer to the “why.” But that conclusion seems to me to be on shaky ground. It is largely based on the fact that climate models do not predict an occurrence like the 2012 drought from greenhouse gas emissions. Yet, it is well known that climate models do a poor job of predicting climate change on local/regional scales, and especially in the case of precipitation. (See here and here.)

Even the authors recognize the shaky ground upon which their conclusion stands. The following caveat with regard to the climate-change conclusion appears on page 31 [pdf] of the report: “This is not intended to be a comprehensive assessment of the possible effects of global warming on the 2012 central Plains drought, and hence results here are inconclusive.” A caveat that the media seems to have missed in their reportage.

“No Way,” Says Climate Scientist Kevin Trenberth

When it comes to the NOAA report’s conclusion that climate change did not play a role in the 2012 drought, Kevin Trenberth of the National Center for Atmospheric Research goes a bit further than a mere caveat. You can find Trenberth’s commentary on the report at ClimateProgress.

Of the report Trenberth writes:

“It is quite incomplete in many respects, and it asks the wrong questions. Then it does not provide very useful answers to the questions that are asked. … It 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.”

With regard to the use of climate models, he writes:

“In the experiments performed with climate models, no indication is given that the model used or the forecast results from several other models, have any skill or utility at the task set them. … The model biases are not dealt with and their skill, or lack of it, is not given. They are not shown to be appropriate to the task at hand. There is a complete failure to provide any reasons to believe the results.”

And:

“The question never addressed is what does global warming and human influences bring to [drought]? There is no discussion of evaporation, or potential evapotranspiration, which is greatly enhanced by increased heat-trapping greenhouse gases. In fact, given prevailing anticyclonic conditions, the expectation is for drought that is exacerbated by global warming, greatly increasing the heat waves and wild fire risk. The omission of any such considerations is a MAJOR failure of this publication.”

OK, Why Don’t I Chime In?

I guess you could say that Trenberth was not enamored in the least by the NOAA report. My own take is not quite as negative. I found the analysis of what happened meteorologically in 2012 and how the drought developed to be interesting and informative.

But what about the report’s conclusion about the non-role of climate change? First of all, and in fairness to Hoerling et al., let’s not forget that they did include a caveat — albeit one buried on page 31 and absent from the summary document. Even so, I finished the report with a significant sense of letdown. And I found the conclusion that the drought occurred because it was dry and hot without any role for warming temperatures from climate change to border on being myopic.

Here’s an analogy — perhaps a bit extreme but I think on point: You’re at Yankee Stadium (or Fenway Park) watching a game. While your back is turned, you get hit in the head by a baseball. Upon careful analysis, you conclude that the collision of your head and the ball was caused because the baseball was flying through the air in your direction.

You’d be correct of course, but really not any wiser or better informed about the need to pay attention when the pitcher throws the ball and the batter gets ready to swing.

So when it comes to climate change, my advice: heads up!

filed under: climate change, drought, faculty, global warming, rainfall, weather
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2 Comments

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  1. Pav Penna
    Apr 25, 2013

    Watched your congressional testimony.

    You really, really should read the conclusions of the IPCC’s SREX document.

    It’s just chock full of neat information that you could use to avoid appearing both dishonest and ill informed at the same time.

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