The human cost of the climate crisis will hit harder, broader and sooner than previously believed, according to a study showing that one billion people will be displaced or forced to endure unbearable heat for every additional 1 ° C rise in global temperature.
In the worst-case scenario of accelerating emissions, areas that currently host a third of the world's population will be as hot as the hottest parts of the Sahara 50 years from now, the newspaper warns. Even in the most optimistic outlook, 1.2 billion people will be left out of the comfortable "climate niche" in which humans have thrived for at least 6,000 years.
The study authors said they were "shocked" and "shocked" by the findings because they didn't expect our species to be so vulnerable.
“The numbers are staggering. I literally did a double take when I first saw them, ”said Tim Lenton of the University of Exeter. “I previously studied climate tipping points, which are generally considered apocalyptic. But this hit harder at home. This puts the threat in very human terms. "
Rather than viewing climate change as a problem of physics or economics, the paper, published in the Proceedings of the National Academy of Sciences, examines how it affects human habitat.
The vast majority of humanity has always lived in regions where average annual temperatures are around 6C (43F) to 28C (82F), which is ideal for human health and food production. But this sweet spot is shifting and shrinking as a result of man-made global warming, leading more people to what the authors describe as "almost impossible to live in" extreme heat.
Humanity is particularly sensitive because we are focused on the land, which is warming faster than the oceans, and because most of future population growth will occur in already warm regions of Africa and Asia. As a result of these demographic factors, the average human will experience a temperature rise of 7.5 ° C when global temperatures reach 3 ° C, which is forecast towards the end of this century.
At that level, approximately 30% of the world's population would live in extreme heat, defined as an average temperature of 29 ° C (84 ° F). These conditions are extremely rare outside the scorched parts of the Sahara, but global warming of 3C is projected to engulf 1.2 billion people in India, 485 million in Nigeria, and more than 100 million each in Pakistan, Indonesia and Sudan.
This would greatly increase migratory pressures and pose challenges to food production systems.
“I think it's fair to say that average temperatures over 29 ° C cannot be lived. You would have to move or adapt. But there are limits to adaptation. If you have enough money and energy, you can use the air conditioner and get good food and then you can be fine. But that's not the case for most people, "said one of the study's lead authors, Professor Marten Scheffer of Wageningen University.
Scheffer said the study began as a thought experiment. He had previously studied the climatic distribution of rainforests and savannah and wondered what the result would be if he applied the same methodology to humans. “We know that most creatures' habitats are limited by temperature. For example, penguins are only found in cold water and corals only in warm water. But we didn't expect humans to be that sensitive. We consider ourselves very adaptable because we use clothing, heating, and air conditioning. But, in fact, the vast majority of people live, and have always lived, within a climate niche that now moves like never before ”.
"We were impressed by the magnitude," he said, adding: "There will be more changes in the next 50 years than in the last 6,000 years."
The authors said their findings should spur policymakers to accelerate emissions cuts and work together to tackle migration because every degree of preventable warming will save one billion people from falling out of the climate niche of the humanity.
"Clearly, we will need a comprehensive approach to protect our children from the potentially enormous social stresses that the projected change could invoke," said another of the authors, Xu Chi of Nanjing University.