At this point, the global climate is about as responsive to human input as a fully loaded supertanker. It will take a great distance — and a very long time — to change direction.

Right now, that supertanker is headed in the wrong direction, and it is picking up speed.

A new scientific report finds that since 2000, greenhouse gas emissions have increased four times faster than they did in the 1990s. They increased by about 3 percent last year as China overtook the United States as the leading carbon dioxide emitter.

It's now likely that the earth's atmosphere contains more carbon dioxide than at any other time in the past 650,000 years. It is 37 percent higher than it was before the Industrial Revolution began around 1750.

Carbon dioxide emissions are growing even faster than the worst-case scenarios put forward by the Intergovernmental Panel on Climate Change, which is the United Nations-sponsored organization established to track and study climate change. And emissions are expected to continue increasing for years to come, despite international efforts to cap them.

Emissions are only part of the problem. In the past, the world's oceans, jungles and forests acted as so-called carbon sinks, absorbing as much as half of the carbon dioxide released by the burning of fossil fuels.

But Brazilian government officials said this week that the Amazon rain forest is being deforested twice as fast as it was last year, reversing what had been a welcome slowing of the rate. Meanwhile, changes in ocean temperature, salinity and currents — some of which are related to global warming — are reducing the oceans' ability to absorb carbon dioxide from the atmosphere. That's making an already bad situation worse.

Scientists say it already is too late to prevent some global warming. The amount of carbon dioxide in the atmosphere guarantees that temperatures will continue to rise for years. Research published last month concluded that even if humans stopped releasing all greenhouse gases immediately, the world's average temperature probably would increase by more than 4 degrees Fahrenheit by the end of the century.

The U.N. climate change panel has estimated that temperature increases of between 3.2 and 9.7 degrees could trigger potentially catastrophic environmental changes that include the melting of glaciers and ice sheets around the globe.

Those, however, are projections — predictions about the future. The new scientific report, prepared by the Global Carbon Project, is a measure of what already has happened.

It's long, long past time for the United States to demonstrate some leadership on global climate change. Even though we're no longer the planet's biggest greenhouse gas emitter, we're still responsible for the lion's share of carbon dioxide in the atmosphere.

The Bush administration, which so often has been wrong about global warming, is correct to insist that both developing and developed nations play a role in curbing greenhouse gas emissions.

But the United States also should make forest protection a part of any international global warming agreement. The world can't afford to lose any more of its natural carbon sinks.

Congress should act quickly to cap greenhouse gas emissions. And it must continue to invest in the development of alternative energy technologies and use the persuasive power of tax credits to encourage their adoption.

The longer we wait to set a new course, the longer it will take to change direction. And the closer we'll come to disaster.

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