Recently released e-mails to and from prominent University of Arizona climate scientist Jonathan Overpeck are stirring critics' concerns.

The controversy is whether Overpeck and other scientists pushed colleagues too hard to conform to his global warming theories and failed to heed comments from other scientists that gave weight to skeptics.

Overpeck, however, said critics don't understand how scientists work in crafting major studies such as the reports from the International Panel on Climate Change, for which Overpeck has been a leading author.

The Overpeck e-mails, dating back three years, are among thousands of e-mails hacked last month from the climate research unit at a British university. Overall, climate-change skeptics say some of the British university e-mails show distortions of fact, attempts to delete or ignore important data, or private admissions that the science favoring the existence of global warming isn't as strong as climate scientists have said publicly.

But while nearly 200 e-mails written and received by Overpeck sit in the East Anglia University database, their tone isn't as explosive or controversial as those of some of his colleagues.

In fact, the comment attributed to Overpeck that has drawn the most buzz in the blogosphere during the e-mail fracas is one that it's not clear he actually made.

Still, the messages to and from Overpeck show that there were privately held, scientific uncertainties about some key theories underlying the idea that today's warm weather is human caused, said a skeptic, Canadian economist Ross McKitrick, a professor at Guelph University in Ontario.

The uncertainties are connected to questions about whether today's weather is warmer than that of a millennium ago, he said. Because of poor handling of key scientific data used in many studies, "it is not possible to make confident statistical assertions about the modern era being warmer than the medieval era," McKitrick told the Star last week.

But Overpeck, the director of UA's Institute for the Environment, said his critics simply don't understand the true workings of the Intergovernmental Panel on Climate Change. The e-mails in question were written in 2006 as Overpeck and his colleagues were preparing a report released in spring 2007, and that report clearly spelled out the uncertainties, Overpeck said.

He said the stolen e-mails represent informal discussions among some of the world's best climatology scientists, "hashing out what we know, what we don't know, and how to represent uncertainty, all based on the peer-reviewed literature. They are not writing for the world to see. They are writing for each other."

Overpeck has been a leading climate-change researcher for well over a decade and has worked with some scientists who wrote key e-mails in what has become known as Climategate. He has co-authored a paper with Phil Jones, head of the East Anglia research unit, who has temporarily stepped down from that post while the university investigates the e-mail imbroglio. Overpeck has written two papers with Michael Mann, a climate scientist whose e-mails are under investigation by his employer, Penn State University.

Canadians McKitrick and Stephen McIntyre, author of a widely read blog called Climate Audit and a statistician and part-time mineral-industry consultant, have spent most of the past decade critiquing various IPCC reports.

Many of the questioned e-mails involving Overpeck center on two key issues: whether the 1990s comprised the warmest decade on record for hundreds of years if not longer, and whether the Medieval Warm Period from 800 to about 1,400 was warmer than today.

In interviews with the Star, McIntyre and McKitrick focused on e-mails from John Mitchell, a British scientist who was a review editor of the 2007 IPCC report.

In June and September 2006, Mitchell wrote Overpeck and Keith Briffa of East Anglia, suggesting they needed to take more steps to answer skeptics' concerns about matters such as the "hockey stick." That's the name for a widely displayed graph, showing flat-lined temperature patterns for up to 1,000 years until a steep rise as the 20th century ended. McIntyre and McKitrick have led the charge against the hockey stick theory. Overpeck at one time embraced the theory but now says it has been rendered moot by later studies.

Overpeck replied to Mitchell's 2006 suggestion by saying he and other colleagues "will be sure to discuss" the questions. But then, according to Mc-Kitrick, "the authors (of the IPCC report) ignored these discussions and Mitchell, for whatever reason, acquiesced." The final 2007 IPCC report showed a temperature graph similar but not identical to the hockey-stick approach.

Overpeck countered that McKitrick doesn't understand the principle of scientific peer-review.

"The role of the review editors was not to determine the outcome, but rather make sure each review comment was dealt with by the author team. Thus, we did not ignore any instructions, nor did Mitchell acquiesce in any way," Overpeck said.

McKitrick said two other 2006 e-mail exchanges between Overpeck and climate research professor Briffa show Briffa was trying to back away from Overpeck's efforts to push him "to sex up the conclusions" on the hockey-stick and medieval-warming issues.

In February 2006, Briffa told Overpeck that there has been only "minimal" independence in how information was gathered for various follow-ups to the original hockey-stick study, published in 1998. (That, said McKitrick, is what he and his colleague have argued - that follow-up studies aren't independent and are reusing the same data.)

"True, there have been many different techniques used to aggregate and scale data, but the efficacy of these is still far from established," Briffa wrote.

The researchers shouldn't push this report's conclusions too hard, Briffa wrote.

"We must resist being pushed to present the results such that we will be accused of bias … . Just need to show the 'most likely' course of temperatures over the last 1,300 years - which we will do well, I think … . Let us not try to over egg the pudding."

Overpeck replied in an interview last week that his job as a contributing author was to strive for the most precise assessment of the science. On multiple occasions, he and other contributing authors pushed lead authors such as Briffa to make sure the text was as clear and precise as possible.

"However, it is VERY important to understand that - as with most good scientific author teams - the other authors are expected to push back, and that this pushing back and forth is what helps arrive at the best articulation of the science," Overpeck told the Star in the interview last week.

To show that McKitrick and other critics are taking his comments out of context, Overpeck pointed to his e-mail to Briffa in 2005 thanking him for making sure the report is being done without bias.

"I **ABSOLUTELY** AGREE THAT WE MUST AVOID ANY BIAS OR PERCEPTION OF BIAS," Overpeck also wrote, in all capitals.

The comment that Overpeck may or may not have made - no one has produced e-mail evidence - was a statement to an Oklahoma researcher back in the 1990s that, "We need to get rid of the Medieval Warm Period."

Overpeck and some of his colleagues have said the Medieval Warm Period wasn't as warm as cracked up to be, or that it was warm only in parts of the world, such as Great Britain or northern Europe, and not globally.

Skeptic Tim Ball of Victoria, B.C., has written essays saying that the reported comment shows Overpeck wanted to eliminate this period to make global warming theories look more scientifically solid.

"If it is Overpeck saying it … they're saying that the end of 20th century is the warmest ever, but we're saying hang on a minute, it was much warmer 1,000 years ago," Ball, a retired professor of climatology at the University of Winnipeg, said in an interview with the Star.

"Were the Vikings driving Volvos? They have to explain this or get rid of it," said Ball, referring to the Medieval Warm Period.

This comment has been repeatedly reported - but without Overpeck's name attached - by longtime warming skeptic David Deming, a geophysicist at the University of Oklahoma. In an article published last March, Deming said that back in 1995, "one of the lead authors" of a just-finished Obama administration report on climate change "told me that we had to alter the historical temperature record by 'getting rid' of the Medieval Warming Period." In 2006 testimony before a U.S. Senate committee, Deming said that in the 1990s, "… I received an astonishing e-mail from a major researcher in the area of climate change. He said, 'We have to get rid of the Medieval Warming Period.' "

For two years now, many bloggers have theorized that Deming was speaking of Overpeck, who before arriving at UA in 1999 was a leading National Atmospherics and Oceanic Administration paleoclimatologist. Reached at his Norman, Okla., home last week, Deming declined to comment.

Overpeck said last week that he had searched through his e-mails dating back a decade, and could find none like Deming referred to. Overpeck pointed out that he has written papers dating to the late 1990s saying that various records, including tree rings, stretching back 1,200 years, confirm earlier assertions that the Medieval period was warmer than today in the North Atlantic and northern Europe - but not globally.

"My papers are the record of fact, and in this case, I obviously did not try to get rid of the MWP," Overpeck said. "Instead, I have tried hard to be clear what it likely was and was not."

Contact reporter Tony Davis at 806-7746 or tdavis@azstarnet.com

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