THIS YEAR, so far, has been the warmest since scientists began keeping records more than a century ago. It wasn't noticeable here in the United States, where the past summer was only a little hotter than normal. The most dramatically unusual weather was in Asia, particularly in Siberia and particularly last March. The 1980s were the warmest decade on record, and now another decade has begun with this unprecedentedly warm year.

That doesn't amount to proof that the world has entered a warming trend that will continue. Nor does it prove that it's being caused by people burning fuel to generate energy. But the evidence is certainly consistent with those possibilities, and this year's temperatures strengthen them.

The White House keeps arguing that the science of global warming is still unclear. True, no one knows whether man-made carbon dioxide has yet begun to make the world hotter or what the consequences might be. But by the time warming becomes provable under the rigorous standards of science, the process will have developed a gigantic momentum, and the world will require decades even to slow it down.

Since the consequences are unpredictable, it doesn't seem very smart to drift headlong into them with as little thought as this country is giving to them. Some of the effects of warming would be benign. Certainly the Soviets, with their economy failing, were grateful for an early spring, much rain and the unusually large harvests that followed. But other impacts may be less welcome. As the people at the White House say, nobody knows.

Most of the world's governments met in Geneva this week to try to work out a joint strategy for cutting down the production of greenhouse gases. The United States was conspicuous in its refusal to commit itself to any reduction or even to accept the need for one. Without the United States, nothing serious is likely to happen worldwide.

The Bush administration fears that any attempt to diminish the emissions of carbon dioxide -- the inevitable result of burning oil, or coal or any fossil fuel -- would be intolerably disruptive and expensive. But not necessarily. There's a lot the United States ought to be doing to reduce its dependence on imported oil, to protect the economy from Middle Eastern oil shocks, to encourage conservation generally and to raise efficiency. By doing that, the country would also reduce the risk of drastic change in the climate. By refusing to deal with the steady rise in carbon dioxide emissions, the Bush administration is ignoring dangers that are literally incalculable.