DESPITE the numerous warnings about extreme weather, rising sea levels and mass extinctions, one message seems to have got lost in the debate about the impact of climate change. A warmer world won’t just be inconvenient. Huge swathes of it, including most of Europe, the US and Australia as well as all of Africa and China will actually be uninhabitable – too hot, dry or stormy to sustain a human population.

This is no mirage. It could materialise if the world warms by an average of just 4 °C, which some scientists fear could happen as soon as 2050. This is …