New Russian heatwave study solves climate conundrum
- 22 Feb 2012, 15:58
- Verity Payne
Russia's record-breaking heatwave of summer 2010 was down to
both man-made climate change and natural variability according to a
new study. In a nuanced conclusion, researchers found that the size
of the heatwave was within natural limits, but the heatwave had
been made three times more likely because of man-made climate
change.
This finding reconciles two previous studies that reached
conflicting conclusions as to the cause of the 60-day heatwave,
which left tens of thousands of people dead from respiratory
illnesses and heat stress, as well as causing numerous wildfires,
failed wheat harvests, and an
estimated $15 bn in financial losses.
Meteorologists
seem
to agree on the immediate trigger of the heatwave: a high
pressure air mass settled over Russia for July and much of August,
diverting the jet stream and the summer storms further north. At
the same time warm continental air was able to spread up across the
region, bolstering the high pressure air mass, and adding to the
heat. The unusually high temperatures are depicted below:
Source:
NASA Earth Observatory
But whether this blocking high pressure system was the result of
natural variability or man-made climate change seems to have been
harder to resolve. In 2011 two separate groups of climate
scientists published seemingly
contradictory results. Randy Dole of the National Oceanographic
and Atmospheric Administration, and colleagues
concluded:
"the intense 2010 Russian heat wave was
mainly due to natural internal atmospheric variability"
whereas Stefan Rahmstorf and Dim Coumou at the Potstam Institute
for Climate Impact Research (PIK)
wrote:
"we estimate ... an approximate 80%
probability that the 2010 July heat record would not have occurred
without climate warming."
Now another research team led by climate scientist Myles Allen
of Oxford University has resolved the conflicting results in their
upcoming paper,
to appear in the journal Geophysical Research Letters.
They ran thousands of climate model simulations, half running
the climate conditions of the 1960s, and the other half the climate
conditions of the 2000s - including the effects of man-made climate
change.
The simulations, run on volunteers' home-PCs as part of the weatherathome.net project,
showed that heatwaves as big as that of Russia in 2010 occurred
even in model simulations using only natural variation. But similar
heatwaves occurred three times as frequently in the simulations
which included man-made climate change.
The apparent contradiction between the two previous studies
arises because Dole and colleagues focused their research on the
size of the heatwave, whereas Rahmstorf and Coumou had looked at
the likelihood of a similar heatwave occurring. As Neil Massey,
University of Oxford and co-author of the study,
puts it:
"These results show that the same
weather event can be both 'mostly natural' in terms of magnitude
and 'mostly human-induced' in terms of probability."
And, Massey explains, this approach has useful practical
implications:
"Thinking in these terms makes it
possible to calculate, for instance, how much human-induced climate
change cost the Russian economy in the summer of 2010."
As is often the case with these issues, there's no simple
answer. Allen
says:
"We have a tendency, whenever a weather
event happens to say 'it was caused by x' but that's never the
case, you have multiple causes for an event. People just have to
learn that there's no such thing as a weather event that has only a
single cause. This is a complicated, interacting system."