18:00 01Dec2004 RTRS-Humans raise risk of Europe heatwaves -scientists

LONDON, Dec 1 (Reuters) - Human activity has raised the risk of more
heatwaves like last year's, which gave Europe probably its hottest summer
since 1500, scientists said on Wednesday.
Tens of thousands of people in Europe died during the sweltering weather
as the mercury soared to new highs.
Unusual meteorological conditions were blamed for the extremely hot, dry
summer. But Peter Stott, of the Hadley Centre for Climate Prediction and
Research in England, said human activity, particularly greenhouse gas
emissions, at least doubled the risk of the unusual event.
"We are responsible for increasing significantly the risk of such
heatwaves, largely through greenhouse gas emissions" Stott told Reuters.
"If we carry on as usual with emissions, our predictions indicate that
every other year will be as hot as 2003 by the middle of the century," he
added.
Stott and his colleagues studied climate change throughout the 20th
century. They suspect human influence probably started altering the climate
as far back as the 18th century.
"But it has only been in the last 50 years that the temperature has
really started to accelerate as a result of greenhouse gas emissions," Stott
said.
The scientists set out to determine the chances of having a European
heatwave like last year's and whether the odds have changed.
Using climate models, they compared what the weather would have probably
been like without any human influences, with simulations that included the
impact of greenhouse gas emissions.
"It showed there was a significant observed warming in Europe that was
associated with increasing greenhouse gas emissions," said Stott, who
reported the findings in the journal Nature.
"We saw that there was a much greater risk of heatwaves now than there
used to be in the pre-industrial climate."
Stott and his colleagues estimated that as much as three-quarters of the
current risk of a heatwave is due to human influence on climate.
In a commentary in the journal, Swiss and German scientists described
the research as a breakthrough because it is the first successful attempt to
detect man-made influence on a specific extreme climate event.
"The advent of such attributable studies might profoundly affect the
course of international negotiations on ways to mitigate, adapt to and
ultimately pay for the consequences of climate change," said Christoph
Schar, at the Institute for Atmospheric and Climate Science in Zurich, and
Gerd Jendritzky, of the German Weather Service in Freiburg.

But Peter Stott, of the Hadley Centre for Climate Prediction and
Research in England, said human activity, particularly greenhouse gas
emissions, at least doubled the risk of the unusual event.

and

Stott and his colleagues estimated that as much as three-quarters of the
current risk of a heatwave is due to human influence on climate.

These figures, ("at least doubled" and "three-quarters") depend very
critically on what is defined as a heatwave, because such events are right at
the tail of a distribution curve. Any statistician would regard them as quite
meaningless as they stand, and statistics is what this is all about. That's
politics, or journalism possibly. Ignore it. I'm not saying it's not going to
get warmer, but as a measure of it these figures mean nothing.

Tudor Hughes, Warlingham, Surrey.