Floods, Heat Hit Europe, but Is It Global Warming?

Thu, 26/07/2007

Computer simulations may soon be able to show how likely it is that extreme weather events such as the floods and heatwaves that swept Europe this week were caused by climate change, scientists say.

"To say you can't blame one event on global warming isn't true," said Oxford University climate scientist Myles Allen.

"We can understand in a lot of detail what's contributing towards the risk of these events."
In its second heatwave this summer temperatures in Greece soared to 45 degrees Celsius (113 Fahrenheit) this week, following an earlier heatwave in June which set a new 110-year record of 46C.

Record temperatures this month have caused up to 500 deaths in Hungary, put 19,000 Romanians in hospital and triggered forest fires across Bulgaria.

And Britain saw this week its worst floods in 60 years, which have left about 350,000 people without running water.

But is it global warming?

Most scientists agree that, if unchecked, manmade climate change caused by emitting greenhouse gases such as carbon dioxide will raise temperatures this century, and make heatwaves and heavy rainfall and storms more common.

It's quite another matter to link one event to global warming, given all the chaotic factors that contribute to the weather. But some scientists think they can do just that.

To Allen it's simply a matter of calculating the probability that global warming was to blame, like quantifying the chance that smoking caused an individual case of lung cancer, or that tampering caused a loaded dice to come up six.

He heads a team which is running thousands of simulations of an individual British flood that happened in 2000, the wettest autumn recorded in 230 years.

The simulations have "borrowed" the computing time of more than 6,000 members of the public, multiplying the modelling power of the experiment.

When logged on to the experiment, each individual computer runs one climate simulation (see http://attribution.cpdn.org/), either with or without manmade greenhouse gas emissions, to identify the contribution of global warming to the flood.

The results will be published later this year, Allen said, and could pave the way for similar studies.


Showing that manmade greenhouse gas emissions have made a particular extreme weather event more likely is not the same as proving beyond doubt that global warming is to blame.
"We've loaded the weather dice towards some of these events happening. We can be very precise about probabilities even if we can't predict the next throw of the dice," Allen said.

Climate scientists are more confident predicting increases in temperature than changes in rainfall.

Hundreds of scientists under the umbrella of the Intergovernmental Panel on Climate Change (IPCC) this year predicted more droughts in Africa and Australia, more floods in Asia, and more heatwaves in southern Europe and North America.

Regarding links to specific heatwaves, the journal Nature published research two years ago showing that it was very likely that human influence had at least doubled the risk of a European heatwave as hot as one in 2003 which caused 15,000 premature deaths in France.

Allen's current flood simulation goes a step further, explicitly simulating one event -- a more direct approach.

The heatwave this summer across southeast Europe especially fits climate scientists' expectations.

"It could be a sign of things to come," said Peter Stott, climate scientist at Britain's MetOffice Hadley Centre and an IPCC lead author.

"Hundreds of years ago you would also have got extreme rain and drought. The question is whether the risk has changed."

Hadley Centre research estimates that 2003-type European heatwaves could happen every second year by mid-century, and that the likelihood of a similar event will increase 100-fold by then, unless we curb greenhouse gas emissions.