The groups presented a survey that shows two in five of the 279 climate scientists who responded to a questionnaire complained that some of their scientific papers had been edited in a way that changed their meaning. Nearly half of the 279 said in response to another question that at some point they had been told to delete reference to "global warming" or "climate change" from a report.
The questionnaire was sent by the Union of Concerned Scientists, a private advocacy group. The report also was based on "firsthand experiences" described in interviews with the Government Accountability Project, which helps government whistleblowers, lawmakers were told.
The Democratic chairman of the House panel examining the government's response to climate change said Tuesday there is evidence that senior Bush administration officials sought repeatedly "to mislead the public by injecting doubt into the science of global warming."
Rep. Henry Waxman, D-Calif., said he and the top Republican on his oversight committee, Rep. Tom Davis of Virginia, have sought documents from the administration on climate policy, but repeatedly been rebuffed.
"The committee isn't trying to obtain state secrets or documents that could affect our immediate national security," said Waxman, opening the hearing. "We are simply seeking answers to whether the White House's political staff is inappropriately censoring impartial government scientists."
"We know that the White House possesses documents that contain evidence of an attempt by senior administration officials to mislead the public by injecting doubt into the science of global warming and minimize the potential danger," Waxman said.
The top Republican on the committee criticized the survey (by the Union of Concerned Scientists) and told CBS News, "The survey is what I would call garbage because they pre-selected the number of people that they would survey—probably members who had been disgruntled."
The administration denies it's trying to mislead anyone about global warming, reports CBS News White House correspondent Mark Knoller.
A spokeswoman for the White House Council on Environmental Quality said the accusation that the administration pressured scientists into downplaying the findings of their research are not true. She said the oversight committee has so far been given 10,000 pages of the documents they've requested and still more will be turned over.
Also Tuesday, Sen. Barbara Boxer, D-Calif., sought to gauge her colleague's sentiment on climate change. She opened a meeting where senators were to express their views on global warming in advance of a broader set of hearings on the issue.
Among those scheduled to make comments were two presidential hopefuls — Sens. John McCain, R-Ariz., and Barack Obama, D-Ill. Both lawmakers favor mandatory reductions in greenhouse gas emissions, something opposed by President Bush, who argues such requirements would threaten economic growth.
The intense interest about climate change comes as some 500 climate scientists gather in Paris this week to put the final touches on a United Nations report on how warming, as a result of a growing concentration of heat-trapping gases in the atmosphere, is likely to affect sea levels.
They agree sea levels will rise, but not on how much. Whatever the report says when it comes out at week's end, it is likely to influence the climate debate in Congress.
At the Waxman hearing, the two advocacy groups said their research — based on the questionnaires, interviews and documents obtained through the Freedom of Information Act — revealed "evidence of widespread interference in climate science in federal agencies."
The groups report described largely anonymous claims by scientists that their findings at times at been misrepresented, that they had been pressured to change findings and had been restricted on what they were allowed to say publicly.
NASA scientist Dr. Drew Shindell said that although he has had concerns about the public affairs policy at NASA in the past, he believes there is a new policy of openness at the space administration and he encourages other agencies who study climate change to adopt similar practices, CBS News reports.
Shindell's major complaint had to do with a press release that NASA issued to advertise a study he did. Initially he said it was titled, "Cool Antarctica May Warm Rapidly." But he says this was watered down by his superiors to read, "Scientists Predict Antarctic Climate Change." He said the new title was a "very milk toast title that didn't inspire any interest."
The Union of Concerned Scientists survey involved scientists across the government from NASA and the Environmental Protection Agency to the department's of Agriculture, Energy, Commerce, Defense and Interior. In all the government employees more than 2,000 scientists who spend at least some of their time on climate issues, the report said.
President Bush mentioned global warming in his recent State of the Union speech – the first time he's done that, CBS News correspondent Bob Fuss reports. But Democrats are ready to do something about it.
Boxer has offered the most aggressive bill, one that is touted as reducing these greenhouse gas emissions by 80 percent by mid-century.
Obama and McCain are sponsoring a bill along with Sen. Joe Lieberman of Connecticut, an independent who usually votes Democratic, that would cut emissions by two-thirds by 2050. Another bill, offered by Sen. Jeff Bingaman, D-N.M., would halt the growth of carbon emissions by 2030 and then is expected to lead to reductions.
All three would require mandatory caps on greenhouse gas releases from power plants, cars and other sources. They also would have various forms of an emissions trading system to reduce the economic cost.