Chris Horner, a senior fellow at the Competitive Enterprise Institute, said NASA has refused for two years to provide information under the Freedom of Information Act that would show how the agency has shaped its climate data and would explain why the agency has repeatedly had to correct its data going as far back as the 1930s. « I assume that what is there is highly damaging, » Mr. Horner said.

The numbers matter. Under pressure in 2007, NASA recalculated its data and found that 1934, not 1998, was the hottest year in its records for the contiguous 48 states. NASA later changed that data again, and now 1998 and 2006 are tied for first, with 1934 slightly cooler.

The Freedom of Information Act requires agencies to respond to requests within 20 days. Mr. Horner says he’s never received an official acknowledgement of his three separate FOIA requests, but has received e-mails showing the agency is aware of them.