Evidence of processing coal in what’s called a “beehive coke oven” in China has been found dating as far back as the fourth century, and the technology involved has not changed much since. Beehive-shaped ovens are used to cook mined coal to turn it into coke, the preferred starting material for making iron and steel. Coke is also desirable since it has a higher proportion of combustible carbon than coal, so it burns better. The processing causes its volatile exhaust gases to be burned off and released into the atmosphere.

China banned beehive coke ovens in 1996. Yet, as a new analysis of the effects of this ban points out, “The poor implementation of environmental laws and regulations is common in China.” So the ovens did not actually disappear until 2011. The authors of the analysis hoped to quantify the effects of the ban—and the lackadaisical approach to enforcing it—on China’s health and environment. They hope that their data will strengthen the resolve of those who seek to pass—and enforce—similar laws in the future.

The authors used official government statistics and satellite images to track the emissions of polycyclic hydrocarbons and the incidence of lung cancer, checking their correlation with beehive coal oven use. In addition to the real-world data, they modeled two scenarios: (a) if no ban had ever been put in place; (b) if the ban had gone instantly into effect in 1996.