A new study by Rahmstorf and Coumou makes an explicit link between climate change and Western Russia’s long, brutal heat wave of July 2010, which caused numerous deaths, plunged Moscow into a sea of smog, and decimated the country’s wheat crops (leading officials to ban all grain exports). The study is significant as it contradicts earlier findings by Dole et al that seems to have confused, in Rahmstorf’s words, “an absence of evidence,” with “evidence of absence.” The authors assert that the “2010 Moscow heat record is, with 80% probability, due to the long-term climatic warming trend.” To get there, the authors used an approach called a “Monte Carlo simulation.” It involved creating two simulations – one based on a century of Moscow’s average July temperatures, which show a clear warming trend, and another which included no warming trend at all. The researchers then ran each model (or “rolled the dice”) 100,000 times, to see how many times the extreme temperature of 2010 would pop up. They found that for “every five new records observed in the last few years, one would happen without climate change. An additional four happen with climate change.” Hence, an 80% chance that the Russian heat wave is linked to climate change.
But the potential significance of this study goes well beyond Russia. The Monte Carlo method, if replicated across the globe, could make the link between climate change and extreme weather events a whole lot clearer. Any number of extreme weather events whose connections to climate change have been deemed by some as “questionable,” whether they be record heat waves, rainfall, or extreme storms, could be given the Monte Carlo treatment, and assigned a probability.
Furthermore, the study raises a serious question about uncertainty and risk. After Dole et al published their piece which did not find evidence of a climate change link to the Russian heat wave, it was tempting for some to deplore any suggestion that a link might exist. This is despite the fact that the Dole study did not, in fact, present any evidence that a link definitely does not exist. Strangely, in the absence of 100% certainty of a climate change link to a particular weather event, many felt compelled to assume, ironically, that there certainly was no link. Rahmstorf and Coumou’s study show how misguided, and potentially risky, such an insistence can be. If policy-makers and practitioners are to take adequate preventive measures to protect their publics from the risks of extreme weather events, they will need to have information on the probability of such events occurring in a warming world. If that information is not reaching their ears because of an insistence on absolute certainty, some risks that could have been mitigated will go unaddressed.