According to the Climate Vulnerability Monitor – a report by Spanish non-profit organisation DARA – in 2010 climate change shaved 1.6 per cent off global gross domestic product. The figure was calculated by adding the harmful effects of climate change to the problems of the carbon-based economy, such as air pollution.

Previous studies, such as the 2006 Stern Review, concluded that climate change would not become a net cost for decades. But they had not considered climate’s impact on productivity. As the temperature increases, people work less well. “It has been assumed that a hotter living and working environment is nothing to worry about,” says Tord Kjellström of Umeå University in Sweden. “But the 5 billion people living in the hot parts of this planet are already constrained by heat.”

Climate change now costs more than the emissions cuts that are needed to tackle global warming. Such cuts would cost 0.5 per cent of global GDP, whereas the cost of climate change will be 3.2 per cent of GDP by 2030. If the claims stand up, it boosts the case for urgent action, says Cameron Hepburn of the London School of Economics. “Caps on emissions should be much tighter, and carbon prices much higher, than they are now.”