20 August 2010

Another Perspective on the Russian Heat Wave

[UPDATE 8/25: See this interview of NOAA's Marty Hoerling.]

NOAA has this to say about the Russian heat wave of 2010:
Despite this strong evidence for a warming planet, greenhouse gas forcing fails to explain the 2010 heat wave over western Russia. The natural process of atmospheric blocking, and the climate impacts induced by such blocking, are the principal cause for this heat wave. It is not known whether, or to what exent, greenhouse gas emissions may affect the frequency or intensity of blocking during summer. It is important to note that observations reveal no trend in a daily frequency of July blocking over the period since 1948, nor is there an appreciable trend in the absolute values of upper tropospheric summertime heights over western Russia for the period since 1900.

The indications are that the current blocking event is intrinsic to the natural variability of summer climate in this region, a region which has a climatological vulnerability to blocking and associated heat waves (e.g., 1960, 1972, 1988). A high index value for blocking days is not a necessary condition for high July surface temperature over western Russia---the warm summers of 1981, 1999, 2001, and 2002 did not experience an unusual number of blocking days.

A clear understanding of the causes for the 2010 Russian heat wave is important for informing decision makers and the public on whether they need to transition from a preparedness mode of precautionary responses to an adaptation mode involving investment responses and actions. Our assessment indicates that, owing to the mainly natural cause for this heat wave, it is very unlikely that a similar event will recur next summer or in the immediate future (next decade). Whereas this phenomena has been principally related to a natural extreme event, its impacts may very well forebode the impact that a projected warming of surface temperatures could have by the end of the 21st Century due to greenhouse gas increases.