"This paper should be a rallying cry," said Chris Field, a co-author of the study published in the Proceedings of the National Academy of Sciences.

Noting recent media reports about countries and companies making serious commitments to combat climate change, Field said: "This basically says what the challenge is, how serious they need to be."

Field, of the Carnegie Institution's Department of Global Ecology in Stanford, California, said the study found that between 2000 and 2004, worldwide carbon dioxide emissions increased by 3.1 percent a year, about three times as fast as the 1.1 percent rate of increase in the 1990s.

In addition to energy intensity, the speed-up is also due to a rise in how much carbon it takes to make the energy people use. Other factors include growth in world population and individual gross domestic product, the study said.

Field noted the scientific consensus that carbon emissions contribute to global climate change.

Much of the accelerated carbon dioxide emissions come from China, where a fast-growing economy is powered largely by coal-fired energy.

CARBON EMISSIONS FROM DEVELOPING WORLD

The developing world, including India and China, and some of the least-developed countries accounted for 73 percent of the growth in global emissions in 2004 and contain about 80 percent of world population, the study found.

By contrast, the study said the world's richest countries contributed about 60 percent of total emissions in 2004 and account for 77 percent of cumulative emissions since the start of the Industrial Revolution.

The research showed global emissions since 2000 grew faster than in the most extreme scenarios developed by the United Nations Intergovernmental Panel on Climate Change.

The panel has said that global carbon dioxide emissions must fall 50 percent to 85 percent by 2050 to stop the Earth from heating up more than 3.6 degrees F (2 degrees C). Higher temperature rises could prompt more deadly floods, droughts and heat waves.

The Bush administration has pointed to recent declines in US carbon intensity and has set the goal of cutting this measurement by 18 percent over 10 years.

Field called the US government's goal "very modest."

"Historically, since 1980, without doing anything, the carbon intensity of the US economy has gone down about 1.5 percent per year, so when they talk about a goal of getting 1.8 percent per year, it's not much change from where we are now," Field said by telephone.

Another co-author, Gregg Marland of the Oak Ridge National Laboratory in Tennessee, said part of the reason for the decline in US carbon intensity was that many high-carbon manufacturing processes have been moved from the United States to other countries, including China, which sells many of the products made this way to the United States.