As much as 40 per cent of humanity could be living outside the optimal climate for humans by the end of the century if we hit 2.7掳C of global warming. At 1.5掳C of warming, half as many people would be affected.
Among the many ways to quantify the effects of climate change is to consider how a warmer world might change the climate in the places humans have historically lived. at the University of Exeter in the UK and his colleagues previously found that over the past 8000 years, closely associated with where domesticated crops grow best. Human populations are densest in places with an average annual temperature of around 13掳C, with another cluster at 27掳C.
While people have found ways to make their homes in places from Siberia to the Sahara, this 鈥渉uman climate niche鈥� represents a kind of optimum for human flourishing, says Lenton. Climate change could shrink the niche.
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Lenton and his team quantified how many people would be left outside this niche given different scenarios. With 2.7掳C of warming by the end of the century, between 21 and 42 per cent of people would live in areas where the average annual temperature exceeds 29掳C. Assuming a future population of 9.5 billion, that would leave as many as 4 billion people outside the niche, with the greatest number in India at 600 million, followed by 300 million people in Nigeria and 100 million in Indonesia.
However, every bit of warming avoided this century leads to hugely different outcomes, says Lenton. With 1.5掳C of warming 鈥� a target that may already be out of reach 鈥� the study found a six-fold decrease in the number of people in India who would end up outside the niche, a seven-fold decrease in Nigeria and a 20-fold decrease in Indonesia compared with the 2.7掳C scenario. 鈥淢y god, there鈥檚 a lot to play for,鈥� says Lenton.
In 1980, the year the study used as a baseline for population density, just 0.3 per cent of people, or about 12 million people, were exposed to average annual temperature over 29掳C. In 2015, due to both climate and demographic change, that number had increased to 12 per cent of people.
鈥淭hese are the sort of numbers we should have been listening to for years,鈥� says at University College London.
at Carleton University in Ottawa, Canada, says the study helps frame the magnitude of the climate problem, though it might falsely imply migration and conflict are inevitable outcomes of rising temperatures, rather than things people and governments can affect.
People can and already do live outside the niche, but Lenton says many aspects of life are generally more difficult, from to staying to . 鈥淲e don鈥檛 live in a world where everyone is rich enough to try and isolate themselves from the climate,鈥� he says. What鈥檚 more, the analysis doesn鈥檛 account for rising seas, extreme weather or other cascading effects.
搁别蹿别谤别苍肠别:听bioRxiv,
