By Roland Pease
BBC science correspondent
Top scientists have reacted angrily to a US Congressman who has demanded to see the full financial and research records of three climate experts.
The Congressman, Joe Barton, says questions have been raised about a study the experts did on climate history and which is at the heart of the current understanding of global warming.
The dispute surrounds a pair of papers written by Michael Mann, Raymond Bradley and Malcolm Hughes at the end of the 1990s suggesting that the past decade was probably warmer than any other in the last one thousand years.
A graph from the papers, showing a sudden up-turn in temperatures in the 20th Century, has been dubbed the "hockey stick" diagram, and has become an icon of global warming.
As such, it has drawn much of the fire aimed at climate science from sceptics.
The strategy, in the words of one scientist, appears to be guilt by association: if the hockey stick is wrong, then other science indicating global warming must also be suspect.
Republican Congressman Joe Barton waded into the controversy late in June.
In his capacity as chairman of the House Committee on Energy and Commerce, Mr Barton wrote to Mann, Bradley and Hughes.
He demanded they should send details from the whole of their careers, covering sources of funding, whereabouts of raw data, and full computer codes (see box).
His letters also talk of "methodological flaws", "data errors", and of questions about the authors' willingness to share their data.
To quote: "...in recent peer-reviewed articles in Science, Geophysical Research Letters, and Energy & Environment, researchers question the results of [the hockey stick] work. As these researchers find, based on the available information, the conclusions concerning temperature histories - and hence whether warming in the 20th Century is actually unprecedented - cannot be supported by the Mann et al studies... ".
THE LETTERS' DEMANDS
Comprehensive CV detailing all authored climate research
List of grants or other financial support to pursue those studies
Basis on which finance was obtained; any stipulations laid down or agreements sought
Detailed catalogue of data archives, contents and location; including calculations and computer source codes used
Mr Barton also wrote to the chair of the Intergovernmental Panel on Climate Change (IPCC), which reproduced the hockey stick in its 2001 scientific assessment of global warming, and to the director of the National Science Foundation, which funds much of the climate science done in the United States.
The letters were also signed by the Republican chairmen of the Sub-committee on Oversight and Investigations - a body that has previously looked into the Enron and oil-for-food scandals.
The committee is concerned, the BBC was told, that a climate policy that could cost trillions of dollars must be seen to be based on solid data.
Request to withdraw
Many scientists have reacted with astonishment at the aggressive tone of the letters, and the extent of their demands.
Henry Waxman, a Democrat member of the committee, wrote to Mr Barton asking him to withdraw them.
"Some might interpret them as an attempt to bully and harass climate experts who have reached conclusions with which you disagree," he wrote.
Now, the three scientists are making their own formal responses.
Raymond Bradley, with only a hint of irony, welcomes the Congressmen's interest in "the basis for President George Bush's recent statement" acknowledging the consensus on global warming and mankind's role in it.
He adds that "it's absurd" to think the conclusion of the IPCC's assessment on global warming rested on any one figure or table.
Dr Bradley told BBC News he thought the intent behind the letters was to undermine confidence in the IPCC which is currently working on its next assessment due to be published in 2007.
Dr Thomas Crowley, of Duke University, whose own climate reconstructions resemble those of Mann et al argues there is a more general intent to intimidate climate researchers.
He warns about the direction Mr Barton's detailed requests could lead.
"For example, requests could be made to palaeontologists and molecular biologists for all data and files supporting evolution," he writes in EOS, the house journal of the American Geophysical Union.
"Likewise, radiochemists could be entrained into pseudo-scientific debate because of all the massive and magnificent geochronological data that have been gathered over the last few decades."
The issue became even more complex over the weekend when Representative Sherwood Boehlert, chairman of the House Committee on Science, declared a turf war with Mr Barton.
As well as saying the Committee on Energy and Commerce has no jurisdiction over climate science, he admonishes the intervention as "at best foolhardy", and argues that the tone of the original letters reflects on the committee's "inexperience" in matters of science.
And support for Mann, Bradley and Hughes has come from the American Association for the Advancement of Science; from the newly appointed president of the US National Academy of Sciences; from the European Geophysical Union; and from a clutch of individual experts, including Nobel Laureate Mario Molina.
But others are standing up for Congressman Barton.
Myron Ebell, of the Competitiveness Enterprise Institute and a prominent global warming sceptic, told BBC News: "We've always wanted to get the science on trial", and "we would like to figure out a way to get this into a court of law", adding "this could work".