A new study published in the Proceedings of the National Academy of Sciences of the United States of America and led by Professor Will Steffen from the Australian National University has found that with just a 1^oC increase in global average temperatures from the current average, the Earth will be at risk of a “hothouse” climate. In such a climate, feedback processes such as permafrost thaw, Amazon rainforest dieback, a reduction of northern hemisphere snow cover, a loss of Arctic summer sea ice, and a reduction of Antarctic sea ice and polar ice sheets would raise the global average temperatures as much as 5^oC above pre-industrial levels, making parts of the world uninhabitable. Sea levels would rise by between 10 and 60 metres, according to the study. The idea of climate change that spirals out of control is not a new one, but the new study adds some quantitative force to it, and gives greater importance to the Paris Agreement’s more ambitious aim of limiting warming to 1.5^oC above pre-industrial levels (and definitely below 2^oC). Current temperature averages are just over 1^oC above pre-industrial levels.