Instead of slowing down, worldwide carbon-dioxide levels have taken a sudden and alarming jump since the year 2000, an international team...

WASHINGTON — Instead of slowing down, worldwide carbon-dioxide levels have taken a sudden and alarming jump since the year 2000, an international team of scientists reported Monday.

CO2 emissions from fossil fuels — mostly coal, oil and gas — are increasing at three times the rate experienced in the 1990s, they said.

The rapid acceleration could make the battle against global warming even more difficult than it already appears.

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Instead of rising by 1.1 percent a year, as in the previous decade, emissions grew by an average of 3.1 percent a year from 2000 to 2004, the latest year for which global figures are available, the scientists reported in this week’s issue of the Proceedings of the National Academy of Sciences.

“Despite the scientific consensus that carbon emissions are affecting the world’s climate, we are not seeing evidence of progress in managing those emissions,” said Chris Field, director of the Carnegie Institution’s Department of Global Ecology in Stanford, Calif., a co-author of the report.

“In many parts of the world, we are going backward,” Field said. “The trends relating energy to economy growth are definitely headed in the wrong direction.”

The spurt in the CO2 emission rate is especially worrisome because it marks a reversal of a long-term trend toward greater energy efficiency and away from carbon-based fuels, the report’s authors said.

The new report should be viewed with caution, said Michael Oppenheimer, a climate-policy specialist at Princeton University in New Jersey. Economies have been recovering from a recession at the turn of the millennium. And a spike in natural-gas prices has given coal a second wind in developed countries. These short-term factors have probably contributed to the growth in emissions rates, he said.

Yet longer-term forces may be at play. For instance, “There is concern among many experts that factors such as China’s continued, very rapid coal-based growth may not be a blip that would turn around,” he said.

The CO2 acceleration is happening fastest in China and other developing areas. It’s increasing more slowly in the advanced economies of the United States, Europe and Japan, the report said.

“The emissions growth rate in the U.S. has remained nearly steady for the last 20 years, at a little under 1 percent a year,” Raupach said. “The growth rate in Europe has averaged less than half that in the U.S. over those 20 years, but it has increased a little in the last five years.”

Last week, the National Academy of Sciences joined 12 similar bodies from around the world — including Europe, China and Russia — in urging cooperation in reducing carbon usage.

To meet the threat, the Proceedings of the National Academy of Sciences report recommends greater efficiency in transportation and power production and more use of low-carbon or no-carbon energy sources, such as solar, wind and nuclear power.

Material from The Christian Science Monitor is included in this report.