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Carbon number crunching

A new study published in Nature reassesses China’s carbon emissions from fossil fuels and cement production. Image credit - iStockphoto

ORNL data experts aid new analysis of Chinese fossil-fuel carbon emissions

Topic: Clean Energy

A booming economy and population led China to emerge in 2006 as the global leader in fossil-fuel carbon emissions, a distinction it still maintains. But exactly how much carbon China releases has been a topic of debate, with recent estimates varying by as much as 15 percent.

“There’s great scrutiny of Chinese emissions now that they are the world’s largest fossil-fuel emitter,” said Tom Boden from the Department of Energy’s Oak Ridge National Laboratory. “Their economy has grown at such a fast rate, so naturally a lot of attention has turned to their emission estimates.”

As director of the Carbon Dioxide Information Analysis Center (CDIAC) at ORNL, Boden has been tracking the world’s carbon emissions for the past 25 years. CDIAC’s annual inventory of carbon released from fossil fuels by country has become a benchmark dataset for climate change scientists and policymakers.

Boden, ORNL’s Bob Andres, and Appalachian State University’s Gregg Marland, a former ORNL scientist, recently lent their emissions data expertise to a new Nature study that reevaluated China’s emissions from 2000 to 2013. The study, led by Zhu Liu of Harvard University, illustrates how carbon emissions estimates take into account a complex set of variables.

“The fundamental calculation requires knowledge of the amount of fuel consumed and the efficiency of burning or the oxidation rate, but you also have to know the carbon content of the fuel,” Boden said. “The carbon content of coal is different than natural gas or crude oil, and it also differs based on where it comes from. Coal coming out of China has a different carbon composition than West Virginia coal.”

In this new study, the researchers used new provincial-level fossil fuel data and different carbon coefficients that are more representative of Chinese coal. China is also the world’s largest cement producer, and the new study reevaluated China’s releases of carbon dioxide from cement production as well. The team’s revised estimate found that China’s fossil-fuel and cement emissions are approximately 10-14 percent lower than other published inventories including CDIAC’s published estimates. Boden, Andres and Marland helped verify the team’s calculations based on their years of carbon accounting experience.

Although the corrected estimate does not change China’s status as the world’s largest emitter, it will benefit future efforts to project future climates.

“Differences on an order of 15 percent become important at global and regional carbon cycle scales,” Boden said. “For a country that’s emitting something on the order of two gigatons of carbon per year and with growing energy demands and large reserves of coal, it’s important to quantify China’s fossil-fuel emissions well.”

Boden and Andres are researchers in the Climate Change Science Institute at ORNL and are supported by DOE’s Office of Science.

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