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Thursday, October 27, 2011

Climate change, fractional attribution of risk and the Russian Heat Wave

Climate scientists using statistical modeling have estimated an 80 percent chance that climate change was responsible for the July 2010 Russian heatwave.

The paper by Stefan Rahmstorf and Dim Coumou from Germany’s Potsdam Institute for Climate Impact Research - Increase of extreme events in a warming world - was published in Proceedings of the National Academy of Sciences on October 25, 2011 notes:

"For July temperature in Moscow, we estimate that the local warming trend has increased the number of records expected in the past decade fivefold, which implies an approximate 80% probability that the 2010 July heat record would not have occurred without climate warming."

The researchers used a century of average July temperatures for Moscow as their baseline warming trend, then ran their simulation 100,000 times to test how often they achieved results which matched the extreme temperatures recorded in July 2010. The researchers then ran the simulation without the warming trend, then compared the results. They called their computational approach Monte Carlo modeling, named after the famed Monte Carlo casinos.

"For every five new records observed in the last few years, one would happen without climate change. An additional four happen with climate change," said Rahmstorf. "There’s an 80 percent probability" that climate change produced the Russian heat wave, Rahmstorf told Wired magazine.

Some extreme weather events can now be statistically modeled by climatologists to assess the attribution to climate change through statistical modelling of probabilities and fractional attributable risk studies. The most notable example of this modeling is the Human contribution to the European heatwave of 2003 (PDF), but researchers have also recently identified Anthropogenic greenhouse gas contribution to flood risk in England and Wales in autumn 2000 (Abstract).

The statistical study by Stefan Rahmstorf and Dim Coumou contradicts an earlier study by Randall Dole et al that said the Russian heatwave was caused primarily through natural phenomenon called atmospheric blocking. This study, published on March 19, 2011 in Geophysical Research Letters said:

"Analysis of forced model simulations indicates that neither human influences nor other slowly evolving ocean boundary conditions contributed substantially to the magnitude of this heat wave. They also provide evidence that such an intense event could be produced through natural variability alone. Analysis of observations indicate that this heat wave was mainly due to internal atmospheric dynamical processes that produced and maintained a strong and long-lived blocking event, and that similar atmospheric patterns have occurred with prior heat waves in this region. We conclude that the intense 2010 Russian heat wave was mainly due to natural internal atmospheric variability." (Abstract)

Rahmstorf told Wired magazine that the Dole study showed "an absence of evidence, not evidence of absence. We found the evidence."

The analysis by the Dole team was challenged at the time by Kevin Trenberth, head of the Climate Analysis Section for the National Center for Atmospheric Research who said the paper was superficial with an extremely narrow focus lacking analysis of related conditions in the hemisphere. You can read his comments at Joe Romm's Climate Progress article - NOAA: Monster crop-destroying Russian heat wave to be once-in-a-decade event by 2060s (or sooner). Climate Central also reported in depth on the issue in their article - NOAA Scientists Find No Clear Human Connection to Deadly 2010 Russian Heat Wave, But…

Another statistical analysis of the Russian heat wave and temperatures in July was done in November 2010 by Tamino who concluded "Without global warming, Moscow’s July 2010 would have been one for the history books. As global warming drives average temperatures even higher, present citizens of Moscow are likely to see multiple such events in a single lifetime. Which is scary."

Fractional Attribution Risk Assessment

Attribution assessment is still in it's early stages. Climate scientists up until recently have claimed that any one individual extreme weather event cannot be directly attributed to climate change. Rahmstorf, Michael Mann and others claimed at the time of Katrina's destruction of New Orleans that "For a single event, regardless of how extreme, such attribution is fundamentally impossible."

Yet, here we are 6 years later with a number of scientific studies attributing causation probabilities of single extreme weather and climate events to climate change and anthropogenic global warming.

"My thinking has evolved," says Gavin Schmidt, a climate modeller at the NASA Goddard Institute for Space Studies in New York. Thanks to advances in statistical tools, climate models and computer power, "attribution of extremes is hard — but it is not impossible", he told Nature News in September 2011.

In 2009 an international scientific working group was established called Attribution of Climate Events to develop research in this area.

Statistical modelling and fractional attribution risk studies are slowly being applied to climate and weather events to determine the probability of climate change contributing to events and opening the possibility as a predictive tool in the future.

Temperature anomaly events seem particularly suitable to attribution risk analysis, while precipitation events are more difficult to assess. Although even the observed intensification of heavy precipitation events in the Northern Hemisphere has been examined in an article published February 2011 in Nature - Human contribution to more-intense precipitation extremes (Abstract)

Such statistical studies are useful for better public understanding and education of the causes of extreme events, to inform legal contexts such as for litigation, to better devise and refine adaptation strategies, and assist with devising and assessing the success or failure of possible geo-engineering efforts.

A discussion of the development of attribution studies was presented as a community position paper - Attribution of Weather and Climate-Related Extreme Events (PDF 3.4mb) - at the World Climate Research Programme Open Science conference in Denver, 24-28 October 2011. The paper makes an interesting read, even though it doesn't take into account Stefan Rahmstorf and Dim Coumou most recent paper on the Russian heat wave.


  • Stefan Rahmstorf and Dim Coumou, PNAS, 24 October 2011, Increase of extreme events in a warming world (Abstract)
  • Randall Dole et al, GRL 19 March, 2011 - Was there a basis for anticipating the 2010 Russian heat wave? (Abstract) GEOPHYSICAL RESEARCH LETTERS, VOL. 38, L06702, 5 PP., 2011 doi:10.1029/2010GL046582
  • Image of Heatwave in Russia from NASA Earth Observatory, August 9, 2010
  • Peter A. Stott et al, Attribution of Weather and Climate-Related Extreme Events (PDF 3.4mb)

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