Sometimes the best intentions can have dire consequences.

This winter, more than half a million families in freezing northern China suffered from insufficient heating or no heating at all. It wasn’t due to a natural disaster, poverty or a lack of development, but was an unintentional consequence of a national policy designed to cut smog and greenhouse gas emissions.

Since 2013, Beijing has been transforming northern China’s extensive district heating market — the largest in the world — by moving it away from coal towards what it calls “clean heating”.