Uncertainties surrounding China's data on carbon emissions threaten to undermine its pledge for a 2030 emissions peak (see Z. Liu et al. Nature 522, 279–281; 2015) and to confuse global strategies for preventing catastrophic climate change. The stakes are high: even small upward tweaks in China's coal consumption could generate more carbon dioxide than many countries emit in an entire year.

Emissions data are a sensitive issue in China, with official government statistical reports focusing more on energy production and consumption than on the country's binding carbon goals. China's carbon data are available for only 1994 and 2005 (through the UN Framework Convention on Climate Change) and are now outdated. Despite high-level policies in 2007 mandating a national greenhouse-gas statistical monitoring system, this has yet to materialize.

China says it reduced its CO2 emissions per unit gross domestic product by 28.5% from 2005 to 2013, but our investigations suggest that more data are needed to confirm this. Clearer justification and methodological explanation is also needed for the frequent revisions of energy statistics by the National Bureau of Statistics of China in Beijing.

As Zhu Liu and colleagues point out, reliable monitoring systems and transparent reporting mechanisms are essential for China's internal emissions management.