China's carbon emissions need to be estimated more accurately if the country is to meet its climate targets and participate in a nationwide emissions-trading scheme after 2017 (see F. Teng Nature 525, 455; 2015). Accounting errors will prevail until the nation's data sources are made transparent, measurable and verifiable.

For example, Teng points to discrepancies between our estimations of coal emissions (Z. Liu et al. Nature 524, 335–338; 2015) and those calculated by the government's data agencies — from information that is not publicly available. The comparison is invalid, however. Our estimates are derived from energy consumption and measured emission factors for coal acquired from 4,845 mines, rather than from final energy consumption and estimated emission factors averaged over all coal types.

Emissions estimates are even more uncertain in economies such as India, Indonesia and South Africa. China's latest investment of 20 billion yuan (US$3.1 billion) for climate-change mitigation and adaptation in developing countries could help these nations to compile measurable, accurate and accessible carbon emissions data.