Natural areas, such as forests or wetlands, absorb some of the carbon released from burning coal, oil or gasoline -- but far from all. North American carbon totals (in billions of tons) annually:
Carbon released: 1.86
Carbon absorbed: 0.51
Net release: 1.35
Source: U.S. Climate Change Science Program
By Patrick O'Driscoll, USA TODAY
North America's ability to absorb global-warming gases created by the USA, Canada and Mexico is smaller than some experts thought and likely to shrink further, a federal climate study said Tuesday.
The report by the U.S. Climate Change Science Program, the Bush administration's climate research arm, estimated the continent produces three to four times more carbon dioxide than its forests, croplands, wetlands and coastal waters can soak up. The rest adds to the warming.
North America emits 27% of the carbon dioxide — the most plentiful of man-made greenhouse gases and the byproduct of burning fossil fuels — released worldwide.
The United States creates 85% of North America's total and is the world's largest emitter, though China is forecast to exceed that soon, according to the International Energy Agency. Canada produces 9%, and Mexico, 6%. Plants, trees, soil, water and other components absorb only about one-fourth of the continent's carbon emissions.
The report put fresh emphasis on the need to slash emissions "if we are interested in mitigating the effects … of climate change," said University of Colorado scientist Lisa Dilling, one of the study's lead authors.
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The report said much of the continent's emissions, 42%, comes from extracting and burning fossil fuels for electricity.
Exhaust from cars and other transportation accounts for 31%, it said.
Some of the findings echoed previous studies, including reports last spring by the Intergovernmental Panel on Climate Change, which shared this year's Nobel Peace Prize with former vice president Al Gore. The IPCC will issue its final report Saturday in Spain, synthesizing its conclusions on the eve of the United Nations' annual climate conference, set for Dec. 3 in Indonesia.
The analysis on the amount of carbon dioxide absorbed by vegetation is new and significant, said co-author Anthony King of the Oak Ridge (Tenn.) National Laboratory.
He said past studies suggested North America was able to absorb enough CO
to offset emissions. This study, the first net-carbon report for the region, shows such areas are declining and could worsen as climate changes, he said.
"If you burn a forest, it's going to (release) its carbon. And warmer, drier climates are likely to have more forest fires," King said. "Drought would slow down the carbon intake" as well.
Plants absorb carbon dioxide, which helps them grow. King said the regrowth of woodlands cleared in the 19th century for farms or logged for timber is the main factor in absorbing carbon. But, he said, that is declining as forests grow older.
The authors note many uncertainties. "Some studies show increased carbon dioxide will cause forests to grow a little more as well," Dilling said.