China's stated CO2 figures are inconsistent ? by a lot

There's a gap the size of Japan in China's declared carbon emissions.

When researchers added up the emissions declared by each of the 30 provinces in 2010, they found the total was greater than what the country declared as a whole ? by the equivalent of 1.4 billion tonnes of carbon dioxide.

That's the same amount that Japan ? the world's fourth biggest emitter ? pumps into the atmosphere each year, and amounts to about 5 per cent of annual global emissions.

It's not clear how much of this is due to the provinces over-declaring, or the national agency under-declaring.

Dabo Guan of the University of Leeds in the UK and colleagues say there are sometimes opposing political pressures on provincial and national statistics departments. Provincial authorities over-report economic outputs to appear to be performing better, says Guan, but then have to over-report their energy consumption data to match. On the other hand, national policies of improving energy efficiency put downward pressure on the country-wide statistics.

In addition, almost a third of coal in China is produced by small firms that do not have the personnel to accurately report their data, says Guan.

China's National Bureau of Statistics says the discrepancy is down to the use of different conversion factors, but Guan argues that it can't explain the discrepancies. He found similar differences between the national and provincial declared use of coal, which explain most of the gap.

Co-author Yong Geng, at the Chinese Academy of Sciences, said he thought the lower, national figure was probably more reliable.

Journal reference: Nature Climate Change, DOI: 10.1038/nclimate/1560

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