[extropy-chat] Why global warming is anthropogenic

[Damien Broderick]

http://www.timesonline.co.uk/article/0,,3-1490248,00.html

February 19, 2005

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.