New USA Govt Report on Global Warming 2006-06-25Posted by clype in Science.
A report requested by the US American Congress has found that there is enough scientific evidence to conclude that the past few decades have been the warmest in the past 400 years.
It is less certain, though 'probable', that the past 25 years have also been the warmest since the year 900, say the authors of the report from 'The National Academies of Science' ('NAS'), the non-profit body that advises the USA government.
They also conclude that humans may have influenced the recent warming.
While some people 'have attempted to promote the idea that the recent warming is a natural phenomenon' unconnected with human activity, 'this report renders that notion much less plausible', comments the President of 'The Royal Society' Mr.Martin Rees on the findings.
The report paid particular attention to the controversial findings of two papers published by palaeoclimatologist Mr.Michael Mann and his colleagues in the late 1990s ('Geophysical Research Letters', vol.26, pp.759-762; and 'Nature', vol.392, pp.779-787).
These seminal studies used a wide range of evidence — including tree rings and historical records — to reconstruct average temperatures of the northern hemisphere over past centuries.
The 'hockey stick' graph from Mr.Mann's team, showing the average temperature over the past 1000 years, gained wide attention.
For the first 900 years there was little variation — like the shaft of a hockey stick — and then there has been a massive warming over recent decades — a spike that formed the 'blade' of the graph.
Chairman of the House Science Committee Mr.Sherwood Boehlert, requested the 'NAS' report in 2005-11 in response to the political debate around Mr.Mann's work.
The 'NAS' report finds that conclusions drawn from Mr.Mann's reconstructions of warming over the past 400 years bear weight, but it stresses that there is too little evidence to be statistically certain that a given year or single decade stands out as unusually warm.
Mr.Mann's team had suggested that the 1990s were the warmest decade of the millennium and 1998 the warmest year.
'It was really the first analysis of its type,' panel member Mr.Kurt Cuffey of 'The University of California', Berkeley, USA, said at a news conference on Thursday.
He added that it was the first time anyone has done such a large-scale and continual analysis of temperature over time.
'So it's not surprising that they could have probably done some detailed aspects of it better.'
But it was a remarkable contribution and gave birth to a debate that's ongoing, that's teaching us a lot about how climate has changed.
The 'NAS' document says that humans may have influenced the recent warming but notes:
"Surface temperature reconstructions for periods prior to the industrial era are only one of multiple lines of evidence supporting the conclusion that climatic warming is occurring in response to human activities, and they are not the primary evidence."
The publication of the 'NAS' report comes too late to influence whether or not 'The Supreme Court' will hear its first case on climate change.
Prominent climate change scientists have been urging the USA 'Supreme Court' to hear a case regarding whether the USA federal 'Clean Air Act' compels 'The Environmental Protection Agency' ('EPA') to regulate greenhouse gas emissions from motor vehicles. But Mr.James Milkey, a lead attorney hoping to argue the case for stronger regulation of carbon dioxide pollution from cars, sees the report as a boost nonetheless.
'We certainly think that the report confirms what we've been saying about the science,' he says.
'It will definitely have weight and could definitely be brought to bear on a future case,' says Mr.John Harte of 'The University of California Berkeley', who along with other scientists has urged 'The Supreme Court' to hear the case.
- 'US report backs study on global warming' By Roxanne Khamsi, New Scientist, 2006-06-23 Friday.