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:
Glaciers in the Antarctic and in Greenland are melting much faster than expected, and the fastest moving glacier in the world has doubled its speed.
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, but none of them has persuaded the White House to alter its current climate policy. 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 J. Dobriansky, undersecretary of state for global affairs.
International negotiators are to embark on a new round of climate talks tomorrow as researchers are still struggling with how to measure the effects of global warming and to 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 S. Broecker, a geochemist at Columbia University's Lamont-Doherty Earth Observatory. Broecker believes the United States has to act quickly to counter its contribution to global warming. "If we don't pick up the pace, we're not going to get there."
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.
As a candidate in 2000, Bush flirted with the idea of limiting carbon dioxide emissions, but he dismissed that option during 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 R. 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 E. 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.
Hansen and other proponents of restricting greenhouse gases point to several recent studies that make the case for immediate action. These include 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.