The University of East Anglia, in eastern England, said in a statement yesterday that the hackers had entered the server and stolen data at its Climatic Research Unit, a leading global research center on climate change. The university said police were investigating the theft of the information, but could not confirm whether all the materials posted online were genuine.

More than a decade of correspondence between leading British and U.S. scientists is included in about 1,000 e-mails and 3,000 documents posted on Web sites following the security breach last week.

Some climate-change skeptics and bloggers contend the information shows scientists have overstated the case for global warming, and allege the documents contain proof that some researchers have attempted to manipulate data.

The furor over the leaked data comes weeks before the U.N. climate conference in Copenhagen, when 192 nations will seek to reach a binding treaty to reduce emissions of carbon dioxide and other heat-trapping greenhouse gases worldwide. Many officials - including U.N. Secretary-General Ban Ki-moon - regard the prospects of a pact being sealed at the meeting as bleak.

In one leaked e-mail, the research center's director, Phil Jones, writes to colleagues about graphs showing climate statistics over the last millennium. He alludes to a technique called Mike's Nature trick used by a fellow scientist to "hide the decline" in recent global temperatures. Some evidence appears to show a halt in a rise of global temperatures from about 1960, but is contradicted by other evidence that appears to show a rise in temperatures is continuing.

Michael Mann, who directs the Earth System Science Center at Pennsylvania State University, said in a telephone interview from Paris that skeptics are "taking these words totally out of context to make something trivial appear nefarious."

In the e-mail from 1999, Jones alludes to one of Mann's articles in the journal Nature and writes, "I've just completed Mike's Nature trick of adding in the real temps to each series for the last 20 years (i.e., from 1981 onwards) and from 1961 for Keith's to hide the decline."

Mann said the "trick" Jones referred to was placing a chart of proxy temperature records, which ended in 1980, next to a line showing the temperature record collected by instruments from that time onward. "It's hardly anything you would call a trick," Mann said, adding that both charts were differentiated and clearly marked.

The use of the word trick by Jones has been seized on by skeptics - who say his e-mail offers proof of collusion between scientists to distort evidence to support their assertion that human activity is influencing climate change.

"Words fail me," Stephen McIntyre - a blogger whose climateaudit.org Web site challenges popular thinking on climate change - wrote on his site after the leak of the messages.

However, Jones denied manipulating evidence and insisted his comment had been taken out of context. "The word trick was used here colloquially, as in a clever thing to do. It is ludicrous to suggest that it refers to anything untoward," he said in a statement yesterday.

Jones did not indicate who "Keith" was in his e-mail.

Two other American scientists named in leaked e-mails - Gavin Schmidt of NASA's Goddard Institute for Space Studies in New York, and Kevin Trenberth, of the U.S. National Center for Atmospheric Research, in Colorado - did not immediately return requests for comment.