For at least 6,000 years, the vast majority of humans have thrived in a relatively small ‘climate niche’. Global warming is shrinking the areas considered ideal for human health and food production. Without mitigating greenhouse gas emissions, billions could be exposed to “near-unliveable” extreme heat by 2070, according to a new paper published on 4 May in the Proceedings of the National Academy of Sciences (1).
With every one-degree-Celsius increase in global average annual temperature, around one billion people will be living in temperatures that are too hot to handle. How this affects local populations will largely depend on societal responses. It is becoming increasingly clear that human migration and a shift in agricultural regions will be necessary to adapt to climate change.
If global warming continues, without mitigation or migration a large proportion of the global population will be exposed to temperatures much warmer than they are today, and many will be forced to endure insufferable extreme heat. The number of people affected will depend on how much emissions are reduced by and how fast the global population grows.
These inevitable impacts are what led the international team of researchers to ask the question: What climatic conditions are necessary for human life and where will those conditions be projected to occur in the future? The study, which began as a thought-experiment, showed that for thousands of years humans have concentrated in a surprisingly narrow subset of Earth’s available climates – the so-called climate niche – where average temperatures are between 11 to 15 degrees Celsius.
“This strikingly constant climate niche likely represents fundamental constraints on what humans need to survive and thrive”, explained Prof Marten Scheffer of Wageningen University, one of the authors.
What does this mean for the future?
Under the worst-case scenario for population growth and for carbon emission, the authors predict that around 30 per cent of the world’s population could be living in extreme heat by the end of the century, defined as an average temperature of 29 degrees Celcius – currently only seen in the most remote, heat-scorched regions of the Sahara Desert.
But even less severe scenarios predict that in 50 years, at least two billion people will be living in places too hot without air conditioning. “We were blown away by the magnitude”, said Sheffer. “There will be more change in the next 50 years than in the past 6,000 years”.
Most humans will experience a temperature increase of 7.5 degrees Celcius when global temperatures increase to 3 degrees Celcius above pre-industrial levels, which would place 1.2 billion people in India, 485 million in Nigeria, and more than 100 million in each of Pakistan, Indonesia, and Sudan in ‘near-unliveable’ temperature conditions.
Many people do live in warmer and colder places, but the farther the temperatures are from the sweet spot, the harder it becomes to survive. There are currently about 20 million people affected by extremely high temperatures, which is around one per cent of the Earth’s land.
Unfortunately, those who stand to be most affected by further increases in temperature due to human-induced climate change are among the poorest in the world – with the least capacity to adapt. The authors hope these results will drive policymakers toward actions to curb greenhouse gas emissions and to prioritise human development in areas most at risk.
(1) Xu, C. et al. Future of the human climate niche. Proceedings of the National Academy of Sciences (2020). DOI: 10.1073/pnas.1910114117