Varied Views on Extreme Weather in a Warming Climate (Dot Earth, N.Y.Times)

May 11, 2012, 9:28 AM

By ANDREW C. REVKIN
 
drought in oklahomaShawn Yorks/The Guymon Daily Herald, via Associated PressA message from the residents of Hough, Okla., in late June, 2011. More Photos »

[May 15, 6:01 p.m. | Updated |
Here's a fresh post examining the climate arguments of James Hansen and Martin Hoerling.]

Through decades of work, James E. Hansen of NASA has earned his plaudits as a climate scientist. But his intensifying personal push for aggressive cuts in emissions of greenhouse gases has come with a framing of climate science that is being criticized by some respected researchers for stepping beyond what peer-reviewed studies have concluded.

Here is a critique of “Game Over for Climate,” Hansen’s Op-Ed article in The Times this week, from Martin Hoerling, who runs an effort by the National Oceanic and Atmospheric Administration to assess the forces contributing to extreme weather events, followed by a must-read reaction to both from Kerry Emanuel of the Massachusetts Institute of Technology:

Martin Hoerling:

In his recent New York Times Op-Ed piece, Jim Hansen asserts:

“Over the next several decades, the Western United States and the semi-arid region from North Dakota to Texas will develop semi-permanent drought, with rain, when it does come, occurring in extreme events with heavy flooding. Economic losses would be incalculable. More and more of the Midwest would be a dust bowl. California’s Central Valley could no longer be irrigated. Food prices would rise to unprecedented levels.”

He doesnt define “several decades,” but a reasonable assumption is that he refers to a period from today through mid-century. I am unaware of any projection for “semi-permanent” drought in this time frame over the expansive region of the Central Great Plains. He implies the drought will be due to a lack of rain (except for the brief, and ineffective downpours). I am unaware of indications, from model projections, for a material decline in mean rainfall. Indeed, that region has seen a general increase in rainfall over the long term during most seasons (certainly no material decline). Also, for the warm season when evaporative loss is especially effective, the climate of the central Great Plains has not become materially warmer (perhaps even cooled) since 1900. In other words, climate conditions in the growing season of the Central Great Plains are today not materially different from those existing 100 years ago. This observational fact belies the expectations from climate simulations and, in truth, our science lacks a good explanation for this discrepancy.

The Hansen piece is policy more than it is science, to be sure, and one can read it for the former. But facts should, and do, matter to some. The vision of a Midwest Dustbowl is a scary one, and the author appears intent to instill fear rather than reason.

The article makes these additional assertions:

“The global warming signal is now louder than the noise of random weather…”

This is patently false. Take temperature over the U.S. as an example. The variability of daily temperature over the U.S. is much larger than the anthropogenic warming signal at the time scales of local weather. Depending on season and location, the disparity is at least a factor of 5 to 10.

I think that a more scientifically justifiable statement, at least for the U.S. and extratropical land areas is that daily weather noise continues to drum out the siren call of climate change on local, weather scales.

Hansen goes on to assert that:

“Extremely hot summers have increased noticeably. We can say with high confidence that the recent heat waves in Texas and Russia, and the one in Europe in 2003, which killed tens of thousands, were not natural events — they were caused by human-induced climate change.”

Published scientific studies on the Russian heat wave indicate this claim to be false. Our own study on the Texas heat wave and drought, submitted this week to the Journal of Climate, likewise shows that that event was not caused by human-induced climate change. These are not de novo events, but upon scientific scrutiny, one finds both the Russian and Texas extreme events to be part of the physics of what has driven variability in those regions over the past century. This is not to say that climate change didn’t contribute to those cases, but their intensity owes to natural, not human, causes.

The closing comment by Hansen is then all the more ironic, though not surprising knowing he often writes from passion and not reason:

“The science of the situation is clear — it’s time for the politics to follow. ”

Let me borrow from a recent excellent piece in New Scientist by tornado expert Dr. Harold Brooks regarding the global warming and tornado debate, and state:

“Those who continue to talk in certain terms of how local weather extremes are the result of human climate change are failing to heed all the available evidence.”

Kerry Emanuel:

I see overstatements on all sides. Extreme weather begets extreme views. On the Russian heat wave, Marty is citing a single paper that claims it had nothing to do with climate change, but there are other papers that purport to demonstrate that events of that magnitude are now three times more likely than before the industrial era.

This is a collision between the fledgling application of the science of extremes and the inexperience we all have in conveying what we do know about this to the public. A complicating factor is the human psychological need to ascribe every unusual event to a cause. Our Puritan forebears ascribed them to sin, while in the 80’s is was fashionable to blame unusual weather on El Niño. Global warming is the latest whipping boy. But even conveying our level of ignorance is hard: Marty’s quotation of Harold Brooks makes it sound as though he is saying that the recent uptick in severe weather had nothing to do with climate change. The truth is that we do not know whether it did or did not; absence of evidence is not evidence of absence.

Regular readers of my work will not be surprised that I align with Emanuel.

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