COPENHAGEN  The decade of 2000 to 2009 appears to be the warmest one in the modern record, the World Meteorological Organization reported in a new analysis on Tuesday.

The announcement is likely to be viewed as a rejoinder to a renewed challenge from skeptics to the scientific evidence for global warming, as international negotiators here seek to devise a global response to climate change.

The period from 2000 through 2009 has been “warmer than the 1990s, which were warmer than the 1980s, and so on,” Michel Jarraud, the secretary general of the international weather agency, said at a news conference here.

The unauthorized release last month of e-mail messages between climate scientists in Britain and the United States has provided new ammunition to global warming skeptics. Some of the messages seemed to suggest that some data be withheld from the public. Mr. Jarraud said the release of the climate analysis was moved up from year’s end to coincide with the international conference on climate change.