In the four years since President Bush took office, scientific sleuths trying to understand the extent of global climate change — and finger the culprits — have come...

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WASHINGTON —

In the four years since President Bush took office, scientific sleuths trying to understand the extent of global climate change — and finger the culprits — have come up with several important new clues:

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• Glaciers in the Antarctic and Greenland are melting much faster than expected, and the world’s fastest-receding glacier, the Grand Pacific in Glacier Bay, Alaska, has doubled its rate.

• Worldwide, plants are blooming several days earlier than they did a decade ago, and animals are migrating toward cooler climates across the globe.

• The oceans have absorbed extra heat trapped in the atmosphere, which indicates Earth’s temperature should rise by another degree Fahrenheit in the coming decades.

The president’s scientific and policy advisers on global warming do not dispute these findings. Rather than endorsing mandatory limits on carbon-dioxide emissions linked to warming, the course embraced by most of America’s allies, the White House is focusing on technological fixes: developing energy sources that burn cleaner or finding ways to extract excess carbon dioxide out of the atmosphere.

“Our approach is founded on sound science, and on trying to address, with different strategies, climate change,” said Paula Dobriansky, undersecretary of state for global affairs.


Buenos Aires talks


International negotiators embark on a new round of climate talks Sunday as researchers are still struggling with how to measure the effects of global warming and predict what’s in store.

“We’re learning fast, but part of what we’re learning is the climate system is really complicated. … I don’t think we’ll ever make the kind of prediction Bush would want,” said Wallace Broecker, a geochemist at Columbia’s Lamont-Doherty Earth Observatory.

The United States is taking part in the Buenos Aires talks even though the administration opted out of the Kyoto Protocol, which will restrict carbon emissions in most industrialized nations starting in 2008. Dobriansky said U.S. officials will try to convince their counterparts that technological change, not government mandates, offers the best chance to preserve both economic growth and the environment.

Bush flirted with the idea of limiting carbon-dioxide emissions as a candidate in 2000, but he dismissed that option his first year in office, saying that “given the limits of our knowledge,” the nation was better off focusing on voluntary emissions reductions and better energy sources. To that end, the administration has poured nearly $8 billion into climate-change research since 2001.

James Mahoney, who oversees this research as assistant secretary of commerce for oceans and atmosphere, said even though researchers have refined computer models, helped design a more sweeping global observation system and improved the world’s overall knowledge of global warming, “We continue to be humbled in the limits of our own knowledge. … It’s a daunting challenge.”

But some of the government’s own scientists, as well as many independent researchers, reject this assessment.

James Hansen, who directs NASA’s Goddard Institute for Space Studies, told a University of Iowa audience in October that the administration is ignoring evidence of “dangerous anthropogenic interference” with the climate. “Anthropogenic” means human-caused, and his phrasing is significant because the United States pledged in 1992, as part of an agreement called the U.N. Framework Convention on Climate Change, to take all necessary steps to combat such interference.

“As the evidence gathers, you would hope they would be flexible,” Hansen said of the administration in an interview. “You can’t wait another decade” to cut carbon-dioxide emissions, he added.


Latest findings


Hansen and other proponents of restricting greenhouse gases point to several recent studies, including a paper this year showing that ocean heat storage — which reflects the difference between the energy the Earth receives from the sun and the heat it emits back into space — rose between 1993 and 2003 at a rate that conforms to current climate models. It also indicates that global temperatures will rise by 1 degree Fahrenheit over the next several decades.

Scientists have also refined their understanding of other factors that could accelerate or temper climate change.

At one point researchers thought warming would cause more water to evaporate and form clouds, which cool the atmosphere. They recently discovered this was not the case.

They also have begun to grasp the complex role that aerosols — the fine particles emitted by cars, power plants and other sources — play. Lighter-colored aerosols, such as car exhaust and power-plant pollution, reflect sunlight and have a cooling effect, while darker ones, such as soot, absorb it. Both types of emissions will affect warming in the future, though scientists are still gauging their influence.

Other researchers have documented concrete indications of global warming’s effects. Plants worldwide are blooming an average 5.2 days earlier per decade, according to Stanford University senior fellow Terry Root; and the opossum, an animal that confined its range to the South as recently as the Civil War, can now be found as far north as Ontario.

When all these indicators “line up in the same direction, what’s the possibility that’s all an accident?” said Stephen Schneider, who co-directs Stanford University’s Center for Environmental Science and Policy and advocates stricter carbon limits.

Some scientists do question the evidence. John Christy, an atmospheric-science professor at the University of Alabama, Huntsville, said that despite a recent study suggesting the Arctic is warming much faster than the rest of the globe, the hottest years for Arctic temperatures in recorded history are 1937 and 1938, and current Greenland temperatures are no higher than 75 years ago.

Myron Ebell, who directs global-warming and international environmental policy for the free-market Competitive Enterprise Institute, said some studies also cast doubt on a U.N. pronouncement in 2001 that the 20th century was likely the warmest in a millennium.

Christy said given the economic costs of imposing tighter controls on energy production, “The Bush administration is doing a more reasonable approach, considering that mandating carbon restrictions will have no measurable effect on what the climate will do.”

Several senior administration officials said that while they agree that greenhouse gases such as carbon dioxide contribute to climate change, restricting these emissions right now would cost jobs. Instead, they said, the government should continue to focus on promoting technologies that will curb pollution.


Practical applications


One example is FutureGen, a $1 billion, decade-long power-plant project to convert coal into gas and store carbon emissions underground. Bush has also sponsored a $1.7 billion, five-year hydrogen car project aimed at eliminating carbon-dioxide emissions from cars.

“The U.S. position is maybe the only rational position, to identify and promulgate application of new technologies,” said White House science adviser John Marburger III.

Advocates of limiting greenhouse gases, however, remain optimistic they will eventually prevail. Christine Todd Whitman, former Environmental Protection Agency administrator in Bush’s first term, said mandatory carbon-dioxide reductions are “going to happen at some point,” in part because multinational corporations will demand that U.S. policy mirror European standards.

Larry Schweiger, president of the National Wildlife Federation, said Bush has an opportunity to outline a new climate policy in his second term.

“If President Bush personally sits down with the scientists and hears what has happened since he first came to office, we can work together to make progress on global warming,” he said.