Environmental study estimates North American carbon debt

A U.S. government science panel published a report Wednesday that quantifies North America's net contribution of carbon to the atmosphere, one of the first baseline studies comparing the continent's emissions and its carbon absorption through vegetation. The results show that the continent's fossil fuel emissions are outpacing the land's natural ability to absorb carbon dioxide by three to one.

The U.S. Climate Change Science Program, a government panel, conducted the study with the help of researchers around North America and a slew of agencies including NASA, the National Oceanic & Atmospheric Administration, and the Department of Energy. The report has been given to Congress.

The study reported that of all the global emission of carbon dioxide into the atmosphere, more than 25 percent comes from North America. The study's scope was limited to North America, so it didn't release data for other continents.

Electricity generation is the single largest contributor to carbon emissions, followed by transportation, according to the study, which drew from the latest data available from 2003 and 2004. More than half of the electricity produced in North America is consumed in buildings, making that one of the largest single causes of emissions on the continent.

In 2003, for example, energy consumption of U.S. buildings resulted in carbon dioxide emissions greater than the total of carbon dioxide emissions of any country in the world except China, according to the report. The United States' energy use in buildings has risen by 30 percent since 1990, corresponding to an annual growth rate of 2.1 percent. One of the largest drivers of carbon emissions today is the expanding size of the American home, according to the report.

It's generally known that North America produces a large amount of carbon dioxide emissions that are released into the atmosphere, but the study is one of the first to weigh the continent's "sources"--or anything that emits more carbon than it pulls back in, such as buildings--against its "sinks." Sinks, such as forested areas, absorb more carbon than they release. But a forest could become a source once the area is deforested, for example.

According to the report, the available vegetation in North America isn't enough to absorb all of the continent's carbon dioxide emissions, which were more than one gigaton per year in 2003. Scientists were uncertain about the future balance of carbon absorption by vegetation, given a growing number of maturing forests that take up less carbon dioxide from the atmosphere.

The CCSP plans to publish 21 reports on the subject of carbon emissions by the end of next year. Its latest is called the "North American Carbon Budget and Implications for the Global Carbon Cycle."

"This information is critical to understanding the factors that shape our global climate," Bill Brennan, acting CCSP director and NOAA's Deputy Assistant Secretary for International Affairs, said in a statement. "The 21 CCSP reports are designed to help scientists answer key questions about climate change, provide the best possible science to stimulate public discussion and assist decision making on key climate-related issues."