Extreme Weather: Russian Heat Wave of Summer 2010 Was Due to Natural Internal Atmospheric Variability
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.
In the present paper, Dole et al. (2011) analyzed the large-scale flow patterns that led to the extreme heat wave of July 2010 and concludes that the heat wave was mainly due to natural internal atmospheric variability. The paper examined several climate model simulations (using a suite of CMIP3 models used in the IPCC climate change documents) with boundary conditions specified by SST (Sea Surface Temperature) distribution, sea ice conditions and also greenhouse gas concentrations. Based on a careful analysis of the model simulations, the authors of this study conclude that "the Russian heat wave was due to internal atmospheric dynamical processes that produced and maintained an intense and long-lived blocking event." The authors further state that the absence of long-term trends in regional mean temperature variability together with model results indicate that "it is unlikely that the warming attributable to increasing greenhouse gas concentrations contributed significantly to the magnitude of the heat wave."
It is of interest here to also consider several recent studies (Lockwood et al., 2010; Woolings et al., 2010; Sillman et al., 2011) showing how winters over Europe have become more severe in recent years as a result of 'blocking' of warm westerly flow which allows cold Arctic air to sweep over parts of western and northern Europe. Furthermore, such atmospheric blocking events may be linked to decreasing sunspots in recent years, according to some climate scientists in the UK.
Atmospheric blocking events are extensively studied at present. It is not clear at this time if such blocking events are part of natural variability or they are linked to solar variability and decreasing sunspots. What is of interest here is the fact that such blocking events in summer could produce a heat wave as it did in summer 2010 and can also produce severe cold winters in Europe, especially if the blocking occurs over eastern region of the North Atlantic Ocean. Whether we see more blocking events in summer or winter in future climate remains to be seen. For now, however, there remains a lack of evidence for a human-added CO2 effect in producing more heat waves.
Sillman, J., Maspoli, M.C., Kallache, M. and Katz, R.W. 2011. Extreme cold winter temperatures in Europe under the influence of North Atlantic atmospheric blocking. Journal of Climate doi:10.1175/2011JCL14075.1 (in press).
Lockwood, M., Harrison, R.G., Woolings, T. and Solanki, S. 2010. Are cold winters in Europe associated with low solar activity? Environmental Research Letters 5 doi:10.1088/1748-9326/5/2/024001.
Woolings, T., Lockwood, M., Masato, G., Bell, C. and Gray, L. 2010. Enhanced signature of solar variability in Eurasian winter climate. Geophysical Research Letters 37 L20805 doi:10.1029/2010GL044601.