One could focus on the rise in average temperatures and wonder to what extent this will increase the chance of weather extremes. One can of course also walk the opposite route: take a witnessed extreme – and examine if that weather event stems from the climate trend.

Sifting through a mailbox full of Geophysical Research Letters over the weekend we discover that is what researchers of the University of Oxford, the UK Met Office’s Hadley Centre and the Royal Netherlands Meteorological Institute KNMI have done with the temperature extreme of the Russian summer of 2010.

That prolonged heat wave brought temperatures to above 40 degrees Celsius in July and August – a +12 degree temperature anomaly. It cost the Russian economy approximately 2 billion dollars in direct damage and missed revenue. And because of continued heat stress for over a month it is estimated that around 55.000 people died [a death toll comparable to the 2003 West-European heat wave].

Yes or no becomes ‘no and yes’

The research group has first examined previous climatological research into the 2010 heat wave. They find first a team of NOAA and the University of Colorado conclude in a 2011 publication in Geophysical Research Letters that – based on climate model simulations – the Russian heat wave should be regarded as extraordinary, but that “such an intense event could be produced through natural variability alone.”

In that same year however two other researchers, including Stefan Rahmsdorf of the Potsdam Institute for Climate Impact Research, write in PNAS that they did find evidence of a climate change link: “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.”

[Our regulars may recall that last percentage. It was echoed by a special IPCC report on extreme weather events – November 2011.]

The Anglo-Dutch research group in their own investigation of the Russian heat wave concludes these two seemingly opposing views do not necessarily contradict each other.

“Here we use the results from a large ensemble simulation experiment with an atmospheric general circulation model to show that there is no substantive contradiction between these two papers, in that the same event can be both mostly internally-generated in terms of magnitude and mostly externally-driven in terms of occurrence-probability. The difference in conclusion between these two papers illustrates the importance of specifying precisely what question is being asked in addressing the issue of attribution of individual weather events to external drivers of climate,” they write in their own publication in Geophysical Research Letters.

Really, let’s all stay friends.

© Rolf Schuttenhelm | www.bitsofscience.org