China's citizens coined the phrase 'APEC blue' to describe the Beijing sky during the Asia-Pacific Economic Cooperation summit in November last year. This transformation from the usual heavily polluted grey was a result of tough 11-day emissions-reduction measures, enforced for the benefit of visiting dignitaries.

A week or two is not enough. China must take prompt action to extend its blue-sky days for the sake of the nation's lungs and the world's climate during the economic boom (see J. Schmale et al. Nature 515, 335–337; 2014) and call for concerted action by offending sectors (see G. Yang et al. Lancet 381, 1987–2015; 2013).