Despite widespread concern over global warming, humans are adding carbon to the atmosphere even faster than in the 1990s, researchers warned Saturday.

Carbon dioxide and other gases added to the air by industrial and other activities have been blamed for rising temperatures, increasing worries about possible major changes in weather and climate.

Carbon emissions have been growing at 3.5 percent per year since 2000, up sharply from the 0.9 percent per year in the 1990s, Christopher Field of the Carnegie Institution for Science told the annual meeting of the American Association for the Advancement of Science.

"It is now outside the entire envelope of possibilities" considered in the 2007 report of the International Panel on Climate Change, he said. The IPCC and former vice president Al Gore received the Nobel Prize for drawing attention to the dangers of climate change.

The largest factor in this increase is the widespread adoption of coal as an energy source, Field said, "and without aggressive attention societies will continue to focus on the energy sources that are cheapest, and that means coal."

Past projections for declines in the emissions of greenhouse gases were too optimistic, he added. No part of the world had a decline in emissions from 2000 to 2008.

Anny Cazenave of France's National Center for Space Studies told the meeting that improved satellite measurements show that sea levels are rising faster than had been expected.

Rising oceans can pose a threat to low level coastal areas as the ocean warms and expands and as water is added from melting ice sheets.

And the rise is uneven, with the fastest rising areas at about 1 centimeter _ 0.39 inches _ per year in parts of the North Atlantic, western Pacific and the Southern Ocean surrounding Antarctica, she said.

Also, highly promoted efforts to curb carbon emissions through the use of biofuels may even backfire, other researchers said.

Demand for biologically based fuels has led to the growing of more corn in the United States, but that means fields were switched from soybeans to corn, explained Michael Coe of the Woods Hole Research Center.

But there was no decline in the demand for soy, he said, meaning other countries, such as Brazil, increased their soy crops to make up for the deficit.

In turn, Brazil created more soy fields by destroying tropical forests, which tend to soak up carbon dioxide. Instead the forests were burned, releasing the gasses into the air.

The increased emissions from Brazil swamp any declines recorded by the United States, he said.

Holly Gibbs of Stanford University said that if crops like sugar and oil palm are planted after tropical forests are burned, the extra carbon released may be balanced by lower emissions from biofuel in 40 to 120 years, but for crops such as corn and cassava it can take hundreds of years to break equal.

"If we run our cars on biofuels produced in the tropics, chances will be good that we are effectively burning rainforests in our gas tanks," she said.

However, there could be benefits from planting crops for biofuels on degraded land, such as fields that are not offering low productivity due to salinity, soil erosion or nutrient leaching.

"In a sense that would be restoring land to a higher potential," she said. But there would be costs in fertilizer and improved farming practices.

In some cases simply allowing the degraded land to return to forest might be the best answer, she said.

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