China's greenhouse gas emissions 'overestimated'

The United Nations and other international bodies have vastly overestimated China's greenhouse gas emissions over the past decade or more, according to a study released on Wednesday.

In2013, for example, China's total carbon emissions were 14 percent less than the figures used by the UN's panel of experts tasked with providing the scientific framework for global climate talks, said the study published in the peer-reviewed journal Nature.

From 2000 to 2013, the country produced nearly 3 billion metric tons less carbon than previously thought, a figure equivalent to roughly one-third of current global annual emissions.

The new estimate does not change China's ranking as the world's top carbon polluter.

"China's total emissions as a country are still well above the second big emitter, which is the United States," said Corinne Le Quere, director of the Tyndall Centre for Climate Change Research in East Anglia.

Nor does it change the overall climate picture. Scientists have long tracked the atmospheric increase in heat-trapping carbon dioxide with great precision.

But only months ahead of UN talks to forge a planet-saving climate pact, it does highlight the importance of having good data, experts said.

The error in this case comes from the difficulty of measuring China's massive consumption of coal, the study found.

Previous calculations did not sufficiently take into account the fact that China, which consumes nearly as much coal as the rest of the world combined, produces and uses a particularly poor grade of the fossil fuel.

"China burns much lower quality coal, which has a lower heat value and carbon content compared with the coal burned in the US and Europe," explained co-author Dabo Guan, a researcher at Tsinghua University in Beijing.

Even if this "dirtier" coal creates more local air pollution, its lower energy content also translates into lower carbon dioxide emissions.

The other factor that allowed for the new, more accurate estimate is China's efforts in gathering data, experts said.

"Good accounting is hard enough for a single factory, but for a nation the size of China the sheer number and diversity of emissions sources" makes it a monumental task, said Dave Reay, a professor of carbon management at the University of Edinburgh.