Air systems that encircle planet can slow to standstill, as greenhouse gas heats Arctic and causes temperature imbalance
Heatwave in 2003 in France. Photograph: Dominique Faget AFP/Getty |
Global warming may have caused extreme events such as a
2011 drought in the United States and a 2003 heatwave in Europe by slowing
vast, wave-like weather flows in the northern hemisphere, scientists said on
Tuesday.
The study of meandering air systems that encircle the
planet adds to understanding of extremes that have killed thousands of people
and driven up food prices in the past decade.
Such planetary airflows, which suck warm air from the
tropics when they swing north and draw cold air from the Arctic when they swing
south, seem to be have slowed more often in recent summers and left some
regions sweltering, they said.
"During several recent extreme weather events these
planetary waves almost freeze in their tracks for weeks," wrote Vladimir
Petoukhov, lead author of the study at the Potsdam Institute for Climate Impact
Research in Germany.
"So instead of bringing in cool air after having
brought warm air in before, the heat just stays," he said in a statement of
the findings in the US journal Proceedings of the National Academy of Sciences.
A difference in temperatures between the Arctic and areas
to the south is usually the main driver of the wave flows, which typically
stretch 2,500km- 4,000km (1,550-2,500 miles) from crest to crest.
But a build-up of greenhouse gases in the atmosphere,
blamed on human activities led by use of fossil fuels, is heating the Arctic
faster than other regions and slowing the mechanism that drives the waves, the
study suggested.
Weather extremes in the past decade include a European
heatwave in 2003 that may have killed 70,000 people, a Russian heatwave and
flooding in Pakistan in 2010 and a 2011 heatwave in the United States, the
authors added.
The authors wrote that they proposed "a common
mechanism" for the generation of waves linked to climate change.
Past studies have linked such extremes to global warming
but did not identify an underlying mechanism, said Hans Joachim Schellnhuber,
director of the Potsdam Institute and a co-author, who called the findings
"quite a breakthrough," he wrote. The scientists added that the
32-year-period studied was too short to predict future climate change and that
natural variations in the climate had not been ruled out completely as a cause.
The study only considered the northern part of the globe,
in summertime. Petoukhov led another study in 2010 suggesting that cold snaps
in some recent winters in Europe were linked to low amounts of ice in the
Arctic Ocean.
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