WASHINGTON — Global warming isn't directly to blame for last summer's deadly — and extraordinary — heat wave in Russia, researchers said in a report Wednesday that came with a climate warning.
"We may be on the cusp of a period in which the probability of such events increases rapidly, due primarily to the influence of projected increases in greenhouse gas concentrations," said the team led by Randall Dole and Martin Hoerling of the U.S. National Oceanic and Atmospheric Administration.
It was the warmest July since at least 1880 in western Russia. The heat wave led to an increase in deaths in the region, as well as drought, fires, increased air pollution and severe crop damage. Also affected by the warming were Belarus, Ukraine and the Baltic nations.
The extreme heat raised questions about links to global warming.
However, the intense heat wave in Russia "was mainly due to natural internal atmospheric variability," the scientists reported in a paper to be published in Geophysical Research Letters.
The cause in this case, they said, was a strong and long-lived blocking pattern that prevented movement of weather systems. Blocking patterns occur when the high-level jet stream develops a sharp wave pattern. This forces storms to move around an area while conditions there stagnate.