Climate

New Study Attributes Fewer Carbon Emissions To China. So Where Did They Go?

CREDIT: AP Photo/Andy Wong

In this Nov. 27, 2014 photo, workers load coal from a truck at a process station for sale in Tangxian in China's Hebei province.

The pollution caused by China’s coal use gets a great deal of attention, and for good reason. It causes health problems in both China and America — helping to kill 4,000 Chinese people per day and traveling across the Pacific Ocean to increase smog levels in the western United States.

China burns four times as much coal as the United States does. Coal is, in large part, why China surpassed the United States as the biggest carbon polluter on the planet in 2006. In two years, despite a massive head start, China will surpass the United States in cumulative greenhouse gas emissions since 1990.

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CREDIT: Harvard University

But a Harvard-led study released last week in Nature found that the carbon pollution caused by burning coal in China is actually 14 percent lower than originally thought.

Researchers found that from 2000 to 2012, total energy consumption was 10 percent higher than the official statistics. Meanwhile, emissions factors — the carbon content of the coal — for coal in China are actually 40 percent lower than what the Intergovernmental Panel on Climate Change (IPCC) assumed. They also found that Chinese emissions from cement production were actually 45 percent lower than thought.

“Altogether, our revised estimate of China’s CO2 emissions from fossil fuel combustion and cement production is 2.49 gigatonnes of carbon in 2013, which is 14 percent lower than the emissions reported by other prominent inventories,” the study’s abstract reads. This is hundreds of millions of metric tonnes of carbon dioxide less than the world thought China was emitting.

Click to enlarge.

Click to enlarge.

CREDIT: Nature

The reason has to do with the way scientists had assumed coal was burned in China. The study found that the coal China uses as fuel actually contains less carbon than assumed, so burning it yields less carbon pollution. Also, the coal is burned less efficiently, yielding less energy and more ash waste. Because China releases no official greenhouse gas emissions information like the United States and other countries do, international organizations have to make broader assumptions for their estimates than normal.

This is one study, however, and some experts noted that it’s premature to draw conclusions from one specific article.

Kevin Trenberth, senior scientist at the National Center for Atmospheric Research, said the study was “unsatisfactory” because it does not address the glaring fact that carbon emissions continue to rise.

Instead of squaring the results with satellite measurements of CO2 emissions, they rely on uncertain and “surely incomplete” estimates, Trenberth told Climate Central.

Ranping Song, the team lead at the World Resource Institute’s China Climate Program, urged caution in using the Nature study to jump to conclusions.

“Experts in China are raising concerns with how these conclusions in the paper have been reached,” he told ThinkProgress. “A one-time sampling is not representative of the emissions of a coal mine or coal plant over time.” Specifically, Song noted that the emissions factors that the researchers compared “are actually not that different.”

As more global emissions come from developing countries, greenhouse gas emissions inventories have become less certain, according to Steven Davis, one of the authors of the study. It’s possible that China’s coal consumption statistics could be revised upward soon — this would offset some of the reductions found in the study.

“One study like this won’t have an impact on China’s climate policy,” WRI’s Song said. “It wouldn’t change the motives at play — you still witness air pollution. It’s absolutely real, both from ordinary people as well as people in high-level government. They are taking actions to reduce emissions.”

The study examined data up to 2013, so actions China has taken since then will not be reflected in the data — which is important, because China has done a lot since then. In 2014, Chinese coal consumption dropped for the first time this century. It has committed to peaking coal by 2020 or earlier, plateauing carbon emissions by or before 2030, and dramatically increasing its renewable energy production. By next year, the last of the coal-fired power plants in Beijing will close.

Still, assuming this study’s conclusions have merit in that China’s coal burning emits even somewhat less CO2 than originally assumed, this does not mean that the global atmospheric carbon dioxide levels are any lower than scientists thought. Either emissions are coming from somewhere else, or natural processes are a little less effective at sucking up atmospheric carbon dioxide than scientists thought.

“The global total emissions are the sum of country emissions, so it would decrease by the same amount,” said study author Davis. “But don’t confuse emissions with atmospheric CO2.”

Davis, an assistant professor at the University of California, Irvine, said it helps to think about this like a bathtub.

“Emissions are how much is coming out of the faucet, and atmospheric CO2 is the level of water in the tub,” he told ThinkProgress. “We’ve revised the emissions, but the levels are unchanged. What this means is that the drain — e.g., how much CO2 is being sucked up by growing plants — must be slower than we thought.”

Changes in how the terrestrial carbon sink works, especially due to land change, “still have huge uncertainties, so those are fluxes we’d expect to take up the slack of this revision,” Davis said.

It’s unclear exactly what natural processes — most often involving plant respiration — could be so different.

Oceans absorb almost a third of the carbon dioxide emissions worldwide. The water itself absorbs CO2, forming carbonic acid — the process of ocean acidifcation. Living phytoplankton also breathe in carbon dioxide, jump-starting the food chain. The bitter irony, according to a recent study in Nature Climate Change, is that more acidic oceans will shift the balance of these critical phytoplankton species, with some dying out altogether. If these trends mean the oceans absorb less CO2 than previously assumed, that could help account for smaller-than-expected Chinese carbon pollution.

It’s possible that worse-than-assumed deforestation could also be somewhat responsible for the extra emissions. A study released Monday found that if humans continue on their current path, the planet will lose an India-sized area of tropical forests by 2050. Total forestation can be measured in large part by satellite photography, but there could be some unanticipated change in how these forests breathe in carbon dioxide.

While it will take more time and research to parse out exactly what is going on with the extra carbon emissions, this serves as a good reminder that carbon pollution anywhere on the planet affects the tenuous balance that has existed between carbon sinks and carbon sources. Take away a carbon sink, burn more carbon-rich fuels, and it gets stuck in the atmosphere, with truly global consequences.