http://www.timesonline.co.uk/article...490248,00.html


Why global warming is not natural
By Mark Henderson, Science Correspondent

Report from the American Association for the Advancement of Science

THE strongest evidence yet that global warming has been triggered by
human activity has emerged from a study of rising temperatures in the
oceans.

The rise in marine temperatures — by an average of 0.5C (0.9F) in 40
years — can be explained only if greenhouse gas emissions are
responsible, research has shown. The results are so compelling that they
should end controversy about the causes of climate change, one of the
scientists who led the study said yesterday.

“The debate about whether there is a global warming signal now is over,
at least for rational people,” said Tim Barnett, of the Scripps
Institution of Oceanography in La Jolla, California. “The models got it
right. If a politician stands up and says the uncertainty is too great
to believe these models, that is no longer tenable.”

Dr Barnett’s team examined seven million observations of temperature,
salinity and other variables in the world’s oceans collected by the US
National Oceanic and Atmospheric Administration and compared the
patterns with those predicted by computer models of potential causes of
climate change.

Natural variation in the Earth’s climate, or changes in solar activity
or volcanic eruptions, which have been suggested as alternative
explanations for rising temperatures, could not explain the data
collected in the real world. Models based on man-made emissions of
greenhouse gases matched the observations almost precisely.

“What absolutely nailed it was the greenhouse model,” Dr Barnett told
the American Association for the Advancement of Science conference in
Washington. Two models, one designed in Britain and one here in the US,
got it almost exactly. We were stunned.”

Climate change has affected the seas in different ways in different
parts of the world: in the Atlantic, rising temperatures can be observed
up to 2,300ft below the surface, while in the Pacific the warming is
seen only up to 330ft down.

Only the greenhouse models replicated the changes that have been
observed in practice. “All the potential culprits have been ruled out
except one,” Dr Barnett said.

The results, which are about to be submitted for publication in a
peer-reviewed journal, should increase pressure on the US Administration
to sign the Kyoto Protocol, which came into force this week, he said.
“It is time for nations that are not part of Kyoto to re-evaluate and
see if it would be to their advantage to join,” he said. “The debate is
not — have we got a clear global warming signal; the debate is — what we
are going to do about it.”

In a separate study a team led by Ruth Curry, of Woods Hole
Oceanographic Institution in Connecticut, has established that 20,000 sq
km of freshwater ice melted in the Arctic between 1965 and 1995. Further
melting on this scale could be sufficient to turn off the ocean currents
that drive the Gulf Stream, which keeps Britain up to 6C warmer than it
would otherwise be.