Carbon Emissions, Intensity Both on the Rise

After 30 years of declining, the amount of carbon dioxide the world is producing per dollar of economic activity started increasing again in 2000, according to a new study of global carbon trends.

Carbon intensity, which measures carbon emissions as a function of economic activity, began rising by about 0.3 percent per year at the start of the new millennium, said "Global and Regional Drivers of Accelerating CO2 Emissions," the study published in this week's Proceedings of the National Academy of Sciences. Carbon intensity had previously been dropping by about 1.3 percent per year since 1970.

"The majority of current emission scenarios for modeling climate through the 21st century assume sustained decreases in the carbon intensity of the global economy, which have not occurred since 2000," said Josep G. Canadell, lead author of the study and executive director of the Global Carbon Project.

While the Earth's carbon intensity has risen, overall carbon dioxide emissions have also increased while the land and oceans' carbon-absorbing capacities are dwindling. Climate change has caused alterations in the wind patterns over the Southern Ocean, causing already carbon-rich water to well up to the surface -- resulting in less ability for the ocean to soak up excess carbon from the atmosphere. And on land, large droughts have hurt plant cover that naturally absorbs large quantities of carbon dioxide.

"(Together), these effects characterize a carbon cycle that is generating stronger-than-expected climate forcing sooner than expected," the study said.

"The new twist here is the demonstration that weakening land and ocean sinks are contributing to the accelerating growth of atmospheric CO2," added Chris Field, a co-author of the study and director of the Carnegie Institution's Department of Global Ecology.

"What we are seeing is a decrease in the planet's ability to absorb carbon emissions due to human activity," Canadell said. "Fifty years ago, for every ton of CO2 emitted, 600 kilograms were removed by land and ocean sinks. However, in 2006, only 550 kilograms were removed per ton and that amount is falling."

That raises concerns, the study's authors said, because natural carbon sinks have so far helped to absorb more than half of all human-caused carbon dioxide emissions.

The study notes that developing economies such as China and India accounted for 73 percent of the growth in global carbon dioxide emissions in 2004. Overall, however, such countries still contributed only 41 percent of the world's total carbon dioxide emissions that year.

Between 2000 and 2006, growing carbon intensity, increased emissions and dwindling carbon sink capacity caused carbon dioxide levels in the atmosphere to rise by 1.93 parts per million per year. That's a much higher rate of increase than was seen in the 1980s and 1990s: 1.58 parts per million and 1.49 parts per million, respectively. Ongoing increases in emissions have brought today's carbon dioxide levels to a total of 381 parts per million -- the highest concentrations seen in the past 650,000 years, "and probably in the last 20 million."

Institutions participating in the study included the Commonwealth Scientific and Industrial Research Organization of Australia, the University of East Anglia and the British Antarctic Survey in the U.K., the Carnegie Institution of Washington, the Department of Global Ecology at Stanford, the Laboratorie des Sciences du Climat et de l'Environnement in France, the National Oceanic and Atmospheric Administration, the Woods Hole Research Center, the Carbon Dioxide Information Analysis Center at the Oak Ridge National Laboratory and the International Institute for Applied Systems Analysis in Austria

Commonwealth Scientific and Industrial Research Organization, "Decline in Uptake of Carbon Emissions Confirmed." URL: (http://www.csiro.au/news/CarbonEmissionsConfirmed.html)