China’s CO2 emissions fell from 2013 to 2016 due to a shift away from smokestack industries and construction as economic drivers, booming power generation from renewable energy and policies to tackle air pollution.

Reduction in CO2 emissions from China, the US and the UK were the primary reasons that global emissions growth stopped over this period.

However in 2016 the Chinese government kick-started another construction boom that has seen demand for steel and other construction materials surge, driving up coal use and emissions in China and pushing global emissions back to growth.

There is major uncertainty around China’s coal use numbers: production increased by 4.5% in 2018 and 3.3% in 2017, according to the government data release, and the figures also show a small increase in coal imports in both years.

Output of coal-fired power and metals, the largest users of coal, increased significantly. Yet the increase in total coal use was reported at only 1% in 2018 and 0.4% in 2017. It’s likely that coal use fell more than reported until 2016 and subsequently has increased more than reported in the past two years.

But one thing is for sure: what happens next in China is crucial for global climate efforts, as well as China’s war on smog at home.

Whether the emissions increase continues into 2019 depends on several things: whether the government responds to economic woes with another round of stimulus to highly polluting smokestack industries or decides to push for economic transformation, moderating energy demand growth; whether the speed of clean energy deployment can grow to meet overall demand growth; and whether the war on smog gets back on track after setbacks this winter.