The United Nations and other international bodies have vastly overestimated China's greenhouse gas emissions over the last decade or more, according to a study released Wednesday.
In 2013, 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, the research showed.

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

The new estimate does not change China's rank 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," commented 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 tasked with forging a planet-saving climate pact, it does highlight the importance of having good data, experts say.

The error in this case comes from the difficulty of measuring China's massive consumption of coal, said the study, published in the peer-reviewed journal Nature.
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 to 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, in other words, 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 say.

- 'China deserves praise' -

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

"China deserves praise," said Le Quere. "It is a big country, they have a lot of different industries. It shows a desire to improve on the statistics they provide."

Nearly three-quarters of the growth in global carbon output from the burning of fossil fuels and cement production between 2010 and 2012 occurred in China.

And about 70 percent of China's total greenhouse gas emissions come from coal, far more than in the United States or the European Union.

The earlier figures for China's emissions were calculated by the Carbon Dioxide Information Analysis Centre (CDIAC) in the United States and the Emissions Database for Global Atmospheric Research (EDGAR) in the EU, both official data sources for the UN's Intergovernmental Panel for Climate Change.

At the end of November, 195 nations will gather in Paris under the UN Framework Convention for Climate Change (UNFCCC) to forge a plan for capping the increase in global temperatures and helping poorer nations deal with climate impacts already in the pipeline.

One of the challenges is creating standards and tools for measuring the scope of the problem and tracking national actions.

"For climate change, the business adage of 'You can't manage what you don't measure' has never rung more true," said Reay.