Dole, R., Hoerling, M., Perlwitz, J., Eischeid, J., Pegion, P., Zhang, T., Quan, X.-W., Xu, T. and Murray, D. 2011. Was there a basis for anticipating the 2010 Russian heat wave? Geophysical Research Letters 38: 10.1029/2010GL046582.
The authors write that "the 2010 summer heat wave in western Russia was extraordinary, with the region experiencing the warmest July since at least 1880 and numerous locations setting all-time maximum temperature records." And as a result, they say that "questions of vital societal interest are whether the 2010 Russian heat wave might have been anticipated, and to what extent human-caused greenhouse gas emissions played a role."
What was done
In broaching this question, Dole et al. used both climate model simulations and observational data "to determine the impact of observed sea surface temperatures, sea ice conditions and greenhouse gas concentrations."
What was learned
The nine U.S. researchers determined that "analysis of forced model simulations indicates that neither human influences nor other slowly evolving ocean boundary conditions contributed substantially to the magnitude of the heat wave." In fact, they say that the model simulations provided "evidence that such an intense event could be produced through natural variability alone." Similarly, on the observation front, they state that "July surface temperatures for the region impacted by the 2010 Russian heat wave show no significant warming trend over the prior 130-year period from 1880-2009," noting, in fact, that "a linear trend calculation yields a total temperature change over the 130 years of -0.1°C." In addition, they indicate that "no significant difference exists between July temperatures over western Russia averaged for the last 65 years (1945-2009) versus the prior 65 years (1880-1944)," and they state that "there is also no clear indication of a trend toward increasing warm extremes." Last of all, they say that although there was a slightly higher variability in temperature in the latter period, the increase was "not statistically significant."
What it means
"In summary," to quote Dole et al., "the analysis of the observed 1880-2009 time series shows that no statistically significant long-term change is detected in either the mean or variability of western Russia July temperatures, implying that for this region an anthropogenic climate change signal has yet to emerge above the natural background variability." Thus, they say their analysis "points to a primarily natural cause for the Russian heat wave," noting that the event "appears to be mainly due to internal atmospheric dynamical processes that produced and maintained an intense and long-lived blocking event," adding that there are no indications that "blocking would increase in response to increasing greenhouse gases."