News Section
Stories from Climate Central's Science Journalists and Content Partners

Scientists Raise Questions on Drought and Climate

Repost This

When the National Oceanic and Atmospheric Administration issued a report on April 11 that seemed to exonerate global warming as a cause of last summer’s historic drought, a reasonable person might conclude that global warming had been exonerated. After all, NOAA is a highly respected organization, and the report’s lead author, meteorologist Martin Hoerling, is a widely respected scientist. 

Judging by the reactions of other respected scientists, though, the idea that global warming is off the hook is probably too hasty. While the report did fail to find a climate-change connection, it also failed to identify any other “proximate” — i.e., direct — cause, either, leaving more questions unanswered than answered. 

Cheyenne Bottoms, Barton County Kansas.
Credit: Corey Raimond/flickr

Some of those other scientists did point to plenty of indirect factors that might well have contributed to the drought, all of them plausibly linked to climate change. Among them: weather systems disrupted by vanishing ice in the Arctic ocean; reduced snowpack in Western mountains, leading to reduced flow in rivers that water the Great Plains; and higher temperatures that have raised the odds of heat waves that dry out the soil.

Kevin Trenberth, a climate scientist with the National Center for Atmospheric Research, put it more straightforwardly than most in a commentary emailed to reporters. “This report,” he wrote, “has some useful material in it . . . But 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.” 

Several climate scientists find the idea of fingering one main cause for the 2012 drought problematic in any case “It’s very unlikely in my view” said Gabriel Vecchi, a climate modeler at NOAA’s Geophysical Fluid Dynamics Laboratory, in an interview, “that an event as extreme as the 2012 drought was caused by any single factor.”

Natural climate variations were undoubtedly one of those factors but that doesn’t mean they were the only one, said Vecchi, who did not contribute to the drought report. Beyond that, which natural variations those might have been, and how they might have been made worse by climate change can be enormously tricky to tease out.

“This is always a fraught area,” said Princeton geoscientist and Climate Central board member Michael Oppenheimer, in an interview. “Attributing individual extreme events to climate forcing has only been done in a very few cases. I’ve never seen a paper that tries to attribute drought to climate change. All you can say is that it has primed the atmosphere to make drought more common.” 

Conversely, he said, it’s difficult to say that a particular event was not attributable, at least in part, to climate change. The failure to see direct evidence of climate change’s influence, said Oppenheimer, “doesn’t mean it didn’t. It just means you haven’t demonstrated that it did.”

One specific criticism leveled at the NOAA report is that while it acknowledged a weather phenomenon known as a “blocking high,” which helped keep rainstorms away from the central plains last summer, it discounted that this was tied to global warming. Others scientists aren’t so sure. While it’s not definitive at this point, research published last year argues that the loss of Arctic sea ice in the summer, caused by global warming, has lessened the temperature difference between the Arctic and temperate zones, potentially altering the air flow that powers the jet stream. That, in turn, could allow high-pressure systems to get stuck over one area for months at a time.

Another criticism addresses the fact that the NOAA report focuses mostly on last summer’s precipitation shortfall. “Precipitation is highly variable from year to year,” said Aiguo Dai, an atmospheric scientist at the State University of New York at Albany, in an interview. Dai said that makes it much trickier to find a specific cause — and, conversely, to rule one out.  But since other factors could well have contributed to the drought, he argued, that narrow focus isn’t reasonable in the first place.

Hoerling and his colleagues didn’t just rule out global warming as a major cause for the 2012 drought: they also ruled out colder-than-normal ocean temperatures in the tropical Pacific. In the past, those have been associated with drought.

“That wasn’t the case last year,” Dai said, and indeed, the report argues that Pacific Ocean temperature wasn’t a factor, either. But, Dai said, “That only excludes one possibility. Greenhouse gases can affect precipitation in many other ways.” 

The bottom line, he said, was that he wouldn’t have ruled out either ocean temperatures or greenhouse gases as playing a factor in the drought. (Hoerling did not respond to an interview request).

So what did the NOAA report cite in the end as the cause of the 2012 drought? “The interpretation,” write the authors, “is of an event resulting largely from internal atmospheric variability having limited long lead predictability.”

But for many scientists, that conclusion doesn’t rule out a role for climate change. For them, it’s just as likely that attributing a short-term regional climate event like the Great Plains drought to a highly complex, long-term planetary phenomenon like the global warming is simply beyond the current limits of the science.

Related Content
Global Warming Not Significant in 2012 Drought: Report
Arctic Warming is Altering Weather Patterns, Study Shows
Drought Has Ties to La Niña, with Global Warming Assist
U.S. Drought is Most Severe Since 1950s, Report Says
Historic Heat Wave Marches On as Drought Expands
Yes, Summers in the U.S. Really Are Getting Warmer
Arctic Warming is Altering Weather Patterns, Study Shows
It’s Official: Arctic Sea Ice Shatters Record Low

Comments

By Dave (Basking Ridge, NJ 07920)
on April 17th, 2013

Personally, I think Hansen’s climate dice analogy is the most reasonable simple answer to attribution questions. I also think that it is absolutely vital that policy makers clearly hear this type of common sense explanation in relation to severe climate events as opposed to, for instance, the questionable conclusions of Hoerling, which have also been a cause of debate in the past.

As far as this widely criticized NOAA study is concerned, no pot shots intended but meteorologists aren’t climatologists.  In Hoerling’s case as a PhD and professor one would hope that the distinction is atypically fine, but it is still a different discipline. Historically meteorologists have tended to lean more towards a contrarian or equivocal view of climate change versus climatologists. Indeed it took the American Meteorological Society all the way until 2012 before it finally officially conceded that AGW is real. I and others might wonder if Hoerling is still ‘catching up’.

Hoerling also previously suggested in a published article that was widely discussed then, that the deadly 2010 Russian heat wave was largely a consequence of natural climate variability.
http://climateknowledge.org/figures/Rood_Climate_Change_AOSS480_Documents/Dole_Russian_Heat_Wave_GRL_2011.pdf Whereas Hansen argued just the opposite: http://www.pnas.org/content/early/2012/07/30/1205276109.abstract Hansen’s arguments make more technical sense to me but overall I think the climate dice analogy remains attractive.

Reply to this comment

By Camburn (North Dakota)
on April 17th, 2013

Question:  It is obvious that no one knows with any high degree of certainty what caused the 2012 drought.

So why be so intent that AGW played a large part?

Droughts come, droughts go.  They are part of climate.

Some are worse than others.

There is NO model presently running that can do regional scale forecasts with any certainty.

Trying to attribute something to climate change with a as known presently nonexistent signal cheapens the science.

Reply to this comment

By Dave (Basking Ridge, NJ 07920)
on April 18th, 2013

In one sense I agree with you Camburn. This Hoerling thing reminds me a little of Crocodile Dundee “…arguing over who owns them is like two fleas arguing over who owns the dog they live on”

On the one hand, we know and are told that AGW is expected to increasingly disrupt the global water supply system and there are strong indications of such trends. We know that AGW is happening all the time and is therefore a component of the current climate system. So clearly, whatever the cause(s) was of the 2012 drought and to the extent that earth’s climate indeed played a role meaning that an army of thirsty aliens from Mars did not actually mysteriously steal all our water one dark night, then AGW would have to have been part of it.

On the other hand the ‘massive 2012 US drought signal’ was clearly either too diffuse to read or some parameter or set of parameters isn’t being taken into account in official drought predictions otherwise the weather guys would have had the means to predict this one. Therefore given the utter failure to predict this drought, it is monumentally clear that we don’t really sufficiently understand the cause of US (at least) droughts to begin with. To me that would seem to suggest that the first order of business is to correct that situation…

Reply to this comment

By Tom Holzel (Litchfield, CT)
on April 20th, 2013

“... it asks the wrong questions. Then it does not provide very useful answers to the questions that are asked.” “

Oh how these “scientists” squirm when they sense their great politically correct edifice start to crumble at its very foundations. The “right” question they wish answered is: “Why are Americans the major cause of Global Warming?” (Any study that deosn’t address that question is “not very useful.”

Reply to this comment

By Tom Thirion with the 'Green Peace Corps' (Colorado Springs CO)
on April 24th, 2013

The southwestern part of the United States is rapidly drying up, creating forest fires, and The Colorado River which brings fresh water to over 30 billion people from 6 western state and northern parts of Mexico and has been named the United States most endangered river.

Take the time to read the book “A Great Aridness”  by a finalist for the Pulitzer Prize in general non- fiction, and won the Push-cart prize in 2008, William debuys, for a very detailed and grand picture of the southwest and the effects climate change has on weather and drought then draw your own conclusions.

Reply to this comment

By Peter Bender (Chicago, Il 60604)
on April 24th, 2013

2012 was an extremely unusual year for drought and heat in my area.  In the middle of March we experienced temperatures at about 80 decrees for 10 days.  As a gardener I noticed.  This was about 30 degrees above average.  Now 1 or 2 days like that is not unusual but 10 days was unprecedented in the records.  That 10 days dried everything out and the moisture did not recover here until January 2013. 
The drought and heat for the rest of the summer was not in itself unprecedented but that 10 days was telling.

Reply to this comment

By Chuck Davies (St Louis, MO 63128)
on April 25th, 2013

All global warming discussion is about carbon diocide trapping heat.  Where does the heat come from - not just the sun.  What is the amount of heat generated by human activity, heat that was not generated in the past and therefore is a direct contribution from human activity toward global warming?

How many btu’s are released into the atmosphere each day from:
each megawatt of electricity generated by coal, gas, or nuclear electric generating plants;
by each gallon of petroleum burned;
by each each electrical motor’s operation;

How much of the sun’s energy is turned to heat captured in each square mile of road/buildings/other man-made structures, rather than used to drive plant growth.  This captured heat is then released back into the environment at night.

How many btu’s are removed from the atmosphere by each cubic mile of ice that melts, by each degree that the oceans warm?  How much warmer will it be when the ice is gone?

WHAT IS THE FUTURE TREND OF THESE IMPACTS?

Reply to this comment

By donald (dallas, tx. 75070)
on April 25th, 2013

It’s been very dry here as well…lol…Too Dry & Not normal. I do wonder about the “Particulates” of heavy metals that
are being dropped on us thru, “Chem-Trails”....as a means of Weather Control might have something to do with this
lack of rain??  At ” geoengineeringwatch.com” it explain some of this and why our military is doing this & using HAARP
to “Cloud Seed” to control weather patterns.  Also, look at what’s fallen into Lake Shasta, California   Aluminum is
64x safe levels and snow on mountains is worse. There’s other heavy metals as well, but I’m no expert.
Do look at the site or Google the info…...lots there & it makes sense.

Reply to this comment

Name (required):
Email (required):
City/State/Zip:
Enter the word "climate" in the box below:

[+] View our comment guidelines.

Please note: Comment moderation is enabled. Your comment will not appear until reviewed by Climate Central staff. Thank you for your patience.