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Posted at 02:13 PM ET, 11/17/2011

NASA scientist Hansen warns “climate dice” already loaded for more extreme weather

As this turbulent year of extreme weather events - from the “heat dome” that built up across the nation’s midsection to “Snowtober” - draws to a close, one of the world’s top climate scientists is out with a new analysis stating unequivocally that at least some extreme events would not have happened without manmade global warming.

OK, so the scientist is James E. Hansen, the outspoken chief climate scientist at NASA’s Goddard Institute for Space Studies. But despite his bold political advocacy in favor of major cuts to greenhouse gas emissions, or perhaps even because of it, Hansen’s scientific work merits attention.

I view him as being on the leading edge of where many other climate experts could eventually wind up. This was the case in 1988, when he warned Congress that global warming had arrived, and it may be the case now, when he says that the connection between extreme weather events and climate change isn’t nearly as fuzzy as most people think, and that we’ve already painted the “climate dice” with more red sides than there used to be.

I’ve criticized Hansen for his political activism before, saying that it might compromise his ability to be seen by the public as an objective scientist. I still think that’s the case - that his research is seen differently now that he spends his free time protesting coal-fired power plants and the Keystone XL oil pipeline. But his original scientific work remains thought provoking, original, and robust, and therefore is deserving of consideration here.

In the new paper, Hansen, along with colleagues Makiko Sato and Reto A. Ruedy, make three points that I find fascinating....

First, they identify natural climate variability as “the greatest barrier to public recognition of human-made climate change.” They find it’s difficult for the general public to discern the signal of manmade climate change through the background noise of natural variability. This especially comes into play in the context of extreme weather events, where the climate change contribution may not be very noticeable.

Percent area covered by temperature anomalies in categories defined as hot, very hot, and extremely hot. ( Jim Hansen/Columbia/NASA )
However - and this brings me to the second key point Hansen (and his colleagues) makes - the odds of certain extreme weather and climate events, such as a brutally hot summer, have already shot significantly upwards when compared to the 1951-1980 average. Using NASA climate data, Hansen and his two coauthors show that: “The climate dice are now loaded to a degree that the perceptive person (old enough to remember the climate of 1951-1980) should be able to recognize the existence of climate change.”

For example, the chance of a summer falling into the “hot” category (as defined using the 1951-1980 averages) is now nearly 70 percent. Interestingly, the odds of a cool summer have fallen more than the odds of a colder than average winter. Using the “climate dice” as a metaphor, Hansen shows that a colored dice that originally had two sides colored red for hot, two sides colored blue for cold, and two sides painted white for average conditions, now has a much different appearance.

In fact, this climate dice now has four of the six sides colored red, and the odds of a cool or average season occupy just one side each.

From Climate Central: This image shows that the average temperature in Moscow for July 2010 was significantly hotter than any year since 1950. The second and third hottest Julys occurred in 2001 and 1972. More information. ( Climate Central )
In addition, Hansen’s bold statements concerning global warming’s role in recent hot summers, such as this past summer in Texas and Oklahoma, are noteworthy. Whereas other studies have come to more guarded conclusions through the use of more sophisticated methods, Hansen says “we can say with a high degree of confidence that events such as the extreme summer heat in the Moscow region in 2010 and Texas in 2011 were a consequence of global warming”. Even if Hansen’s conclusion is an overstatement, the underlying analysis makes it clear that these extreme summers have become more common in recent years.

Also, I think this analysis offers a solid rebuttal to the view that there are always purely meteorological explanations for such extreme events.

“For example, it is said that the Moscow heat wave was caused by an atmospheric “blocking” situation, or the Texas heat wave was caused by La Nina ocean temperature patterns,” Hansen and his colleagues write.

I’ll leave you with this thought to consider the next time a major heat wave or heavy precipitation event takes place, with the caveat that not all unusual events are created equally.

Of course the locations of the extreme anomalies in any given season are determined by the specific weather patterns. However, blocking patterns and La Ninas have always been common, yet the large areas of extreme warming have come into existence only with large global warming. Today’s extreme anomalies occur because of simultaneous contributions of specific weather patterns and global warming. For example, places experiencing an extended period of high atmospheric pressure will tend to develop drought conditions that are amplified by the ubiquitous warming effect of elevated greenhouse gas amounts.

Related: Critique of Hansen analysis from Texas state climatologist John Nielsen-Gammon

By  |  02:13 PM ET, 11/17/2011

Categories:  Latest, Climate Change, Freedman

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