WASHINGTON — The world pumped up its pollution of the chief man-made global warming gas last year, setting a course that could push beyond leading scientists’ projected worst-case scenario, international researchers said yesterday.

The new numbers, called “scary” by some, were a surprise because scientists thought an economic downturn would slow energy use. Instead, carbon dioxide output jumped 3% between 2006 and 2007.

That’s an amount that exceeds the most dire outlook for emissions from burning coal and oil and related activities as projected by a Nobel Prize-winning group of international scientists in 2007.

Meanwhile, forests and oceans, which suck up carbon dioxide, are doing so at lower rates than in the 20th century, scientists said. If those trends continue, it puts the world on track for the highest predicted rises in temperature and sea level.

The pollution leader was China, followed by America, which past data show is the leader in emissions a person in carbon dioxide output. And while several developed countries slightly cut their CO2 output in 2007, the America churned out more.

Still, it was large increases in China, India, and other developing countries that spurred the growth of carbon dioxide pollution to a record high of 9.34 billion tons of carbon. Figures released by science agencies in America, Britain, and Australia show that China’s added emissions accounted for more than half of the worldwide increase. China passed America as the no. 1 carbon dioxide polluter in 2006.

Emissions in America rose nearly 2% in 2007, after declining the previous year. America produced 1.75 billion tons of carbon.

“Things are happening very, very fast,” a professor of environmental sciences at the University of East Anglia and the British Antarctic Survey, Corinne Le Quere, said. “It’s scary.”

A senior staff scientist at the U.S. Department of Energy’s Oak Ridge National Laboratory, Gregg Marland, said he was surprised at the results because he thought world emissions would drop because of the economic downturn. That didn’t happen.

“If we’re going to do something [about reducing emissions], it’s got to be different than what we’re doing,” he said.

The emissions are based on data from oil giant BP PLC, which show that China has become the major driver of world trends. China emitted 2 billion tons of carbon last year, up 7.5% from the previous year.

“We’re shipping jobs offshore from the U.S., but we’re also shipping carbon dioxide emissions with them,” Mr. Marland said. “China is making fertilizer and cement and steel and all of those are heavy energy-intensive industries.”

Developing countries not asked to reduce greenhouse gases by the 1997 Kyoto treaty — and China and India are among them — now account for 53% of carbon dioxide pollution. That group of nations surpassed industrialized ones in carbon dioxide emissions in 2005, a new analysis of older figures shows.

India is in position to beat Russia for the no. 3 carbon dioxide polluter behind America, Mr. Marland said. Indonesia levels are increasing rapidly.

Denmark’s emissions dropped 8%. Britain and Germany reduced carbon dioxide pollution by 3%, while France and Australia cut it by 2%.

Nature can’t keep up with the carbon dioxide from man, Ms. Le Quere said. She said between 1955 and 2000, the forests and oceans absorbed about 57% of the excess carbon dioxide, but now it’s 54%.

What is “kind of scary” is that the worldwide emissions growth is beyond the highest growth in fossil fuel predicted just two years ago by the Intergovernmental Panel on Climate Change, an atmospheric scientist at the Lawrence Livermore National Lab, Ben Santer, said.

Under the panel’s scenario then, temperatures would increase by somewhere between 4 and 11 degrees Fahrenheit by the year 2100.

If this trend continues for the century, “you’d have to be luckier than hell for it just to be bad, as opposed to catastrophic,” a climate scientist at Stanford University, Stephen Schneider, said.