Emissions of carbon dioxide from fossil fuel burning, the main culprit in global warming, have increased three times faster in recent years than they did in the 1990s, international climate researchers reported today.
And human-induced warming may have been responsible for an unprecedented observation reported Monday by a second group of scientists, who said that for the first time in 30 years of U.S. satellite monitoring of Antarctica, there is "clear evidence" of snowmelt on some of the continent's highest and coldest areas.
The carbon dioxide study, published in the Proceedings of the National Academy of Sciences, concluded that the annual rate of increase for emissions of the main greenhouse gas in 2004 was 3 percent -- triple the 1 percent rate during the 1990s.
"This new finding simply highlights the magnitude of the challenge we face," said Christopher Field, director of the Carnegie Institution's Department of Global Ecology at Stanford University. "The bottom line is that we need to make the world more carbon efficient, but in many parts of the world we're going backwards."
The study was led by Michael Raupach of the Australian government science agency, who is also the leader of the Global Carbon Project, which analyzes the world's output of carbon dioxide. Field and climate scientists from France, Germany and Britain also participated.
The scientists concluded that without stronger action to curb greenhouse gas emissions, particularly in the United States, Europe and Japan, the rate of increase will inevitably climb each year.
The rate of carbon dioxide emissions is climbing most rapidly in developing countries, notably China and India. But "it's important to remember that the developed economies, with only 20 percent of the global population, still emit nearly 60 percent of all the fossil-fuel carbon dioxide released each year," Raupach said in an e-mail message to The Chronicle.
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The other report on new evidence for a warming planet came from scientists analyzing data from a satellite called QuikSCAT that has been flying over the Earth in polar orbit since 1999.
Earlier satellites, now operated by the Defense Department, also measured snow cover in Antarctica and found no melting, the scientists said. The QuikSCAT spacecraft carries a unique scatterometer radar that detects changes in winds, ocean currents and snow cover.
After analyzing the data for 2005, Son Nghiem of NASA's Jet Propulsion Laboratory in Pasadena and Konrad Steffen of the University of Colorado at Boulder found that for the first time, the spacecraft had detected wide areas of melted snow in some of the least likely places in Antarctica.
Snowmelt was found only 310 miles from the South Pole, where ice had been thought to be all but permanent, and at elevations as high as 6,600 feet, where it has always been extremely cold.
In several areas, the scientists said, the spacecraft's radar found evidence that the snowmelt continued for as much as a week at a time, with temperatures rising to 41 degrees, before freezing weather returned.
"Warming changes have been seen and measured all over the world," Nghiem said in an interview, "but we have never seen it so widespread in Antarctica. We had thought that for some reason Antarctica was isolated from the effects of warming, and we've been totally surprised to see that it's happening there, too. We've never seen anything comparable there."
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