IF THE United States is ever going to get serious about climate change, it will be because scientists like NASA's James E. Hansen persuade the public that the Bush administration's policy of denial is a prescription for disaster. But the public won't get to hear the truth from Hansen if the administration has its way. Ever since Hansen said in December that unchecked greenhouse gas emissions could make the earth ''a different planet," NASA has tried to control the public appearances and interviews of its premier climate scientist. Instead of muzzling Hansen, President Bush should be listening very carefully.
Hansen and other scientists studied the most recent data, including 2005 temperature readings that made it the warmest year on record, and concluded that policy makers have to be concerned about ''tipping points" in global warming. There could be irreversible changes, such as the breakup of the Greenland or West Antarctic ice sheets, with sea level increases flooding densely inhabited coasts. Another ''tipping point" could occur if warming causes the Gulf Stream current to shut down, which would lead to Siberian conditions in Northern Europe.
If Americans knew more about scenarios like these, they would reject the Bush administration's feel-good mantra that climate change deserves more study but no mandatory action. Effective action would require two policy changes that Bush opposes: raising the fuel-efficiency standards of cars and sport utility vehicles, and capping the carbon dioxide emissions of the nation's electric plants. Carbon dioxide is the main greenhouse gas contributing to global warming. Coal, the fuel that emits the most carbon dioxide, produces 51 percent of the nation's electric power.
The attempted gagging of Hansen, first reported in The New York Times, is just the latest example of the administration obscuring the facts on global warming. In 2002, the Environmental Protection Agency was forced to omit a section on the risks of climate change from an annual report that for six years had included the subject. In 2003, the EPA buried an analysis by its staff showing that a carbon-capping proposal by Senators John McCain and Joseph Lieberman would not cause any serious harm to the economy.
President Clinton, whose record on climate change was scarcely better than Bush's, called it the world's biggest problem at the World Economic Forum in Switzerland on Saturday. It could, he said, ''fundamentally end the march of civilization as we know it, and make a lot of the other efforts that we're making irrelevant and impossible." The presidency of Clinton's successor risks becoming irrelevant if it doesn't take Hansen's warnings seriously.