In handwritten notes on drafts of several reports issued in 2002 and 2003, the official, Philip A. Cooney, removed or adjusted descriptions of climate research that government scientists and their supervisors, including some senior Bush administration officials, had already approved. In many cases, the changes appeared in the final reports.

The dozens of changes, while sometimes as subtle as the insertion of the phrase "significant and fundamental" before the word "uncertainties," tend to produce an air of doubt about findings that most climate experts say are robust.

Mr. Cooney is chief of staff for the White House Council on Environmental Quality, the office that helps devise and promote administration policies on environmental issues. Before going to the White House in 2001, he was the "climate team leader" and a lobbyist at the American Petroleum Institute, the largest trade group representing the interests of the oil industry. A lawyer with a bachelor's degree in economics, he has no scientific training[emphasis added].

In one instance in an October 2002 draft of a regularly published summary of government climate research, "Our Changing Planet," Mr. Cooney amplified the sense of uncertainty by adding the word "extremely" to this sentence: "The attribution of the causes of biological and ecological changes to climate change or variability is extremely difficult." In a section on the need for research into how warming might change water availability and flooding, he crossed out a paragraph describing the projected reduction of mountain glaciers and snowpack. His note in the margins explained that this was "straying from research strategy into speculative findings/musings."

Mr. Cooney's alterations can cause clear shifts in meaning. For example, a sentence in the October 2002 draft of "Our Changing Planet" originally read, "Many scientific observations indicate that the Earth is undergoing a period of relatively rapid change." In a neat, compact hand, Mr. Cooney modified the sentence to read, "Many scientific observations point to the conclusion that the Earth may be undergoing a period of relatively rapid change." [emphasis added]