ST. LOUIS, United States (AFP) - The US space agency NASA is under increasing pressure from Congress and the scientific community to make sure its researchers remain independent after the agency's top expert on climate publicly denounced attempts to censor his work.

The charges, first reported by The New York Times in January, have since been confirmed by other media outlets and NASA public relations officials.

These officials, quoted subsequently by The Times, said White House political appointees had exerted strong pressure on NASA -- particularly during the 2004 election campaign -- to reduce the flow of information from the agency on climate change, the melting of glaciers, and environmental pollution.

White House appointees wanted NASA press releases to refrain from referring to "atmospheric warming" and talk instead about "climate change," said the NASA employees, speaking on conditions of anonymity.

Although these charges have been denied, NASA Administrator Michael Griffin, an engineer widely respected for his integrity, issued two weeks ago an appeal for scientific openness in the space agency.

Griffin, who has been in charge of the agency since April 2005, also called for a review of NASA communications policy.

The NASA official in charge of communications, George Deutsch, resigned last week in the face of accusations he had prevented journalists from interviewing the agency's top climate expert, Jim Hansen.

The revolt by Hansen, who heads the Goddard Space Flight Center, has resonated in the US Congress.

On Thursday, Sherwood Boehlert, the Republican chairman of the House Science Committee, said NASA had still a lot to do to ensure its openness.

In the Senate, the chair of the Governmental Affair Committee, Republican Susan Collins, and her Democratic counterpart, Joseph Lieberman, wrote Griffin a letter demanding an explanation of the controversy surrounding Hansen.

Without denying the existence of global warming, the administration of President George W. Bush has refused to accept limits on greenhouse gas emissions outlined in the Kyoto Protocol, arguing that they will be too costly for the economy.

The administration has said it would prefer to promote technologies that improve energy efficiency.

At a scientific conference here, NASA researchers unveiled a study showing that over the past five years, glaciers in Greenland have been breaking off into the Atlantic nearly twice as fast as previously thought.

Measurements taken since 2000 on Greenland's southeastern glaciers, show that with rising temperatures -- three degrees Celsius in 20 years -- more melted water flows under the glaciers, speeding up their flow to the sea, the researchers said.

"Climate warming can work in different ways, but generally speaking, if you warm up the ice sheet, the glacier will flow faster," said Eric Rignot from NASA's Jet Propulsion Laboratory and the California Institute of Technology.

According to calculations done in light of the new data, the loss of Greenland's ice sheet to the ocean has increased from 50 cubic kilometers (12 cubic miles) per year in 1996 to 150 cubic kilometers (36 cubic miles) in 2005.

Rignot said the new estimates have changed models used to predict sea level rises since Greenland ice is now calculated to contribute 0.5 millimeters (0.04 inches) to the annual global sea level rise of three millimeters (0.12 inches).

In January, Hansen published a study showing that 2005 was the hottest year on record since the 19th century.

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