Global warming will force more than a fifth of the world’s population out of the “climate niche” most conducive to human life by 2100 if temperatures continue rising, a new study estimates, articulating the dire toll across many parts of the world in the coming decades if policymakers do not take sharp action to curtail the worst effects of heat.
By the end of the century, nearly 2 billion people could be living with average annual temperatures hotter than 84 degrees Fahrenheit, or 29 degrees Celsius, the maximum level at which the study’s authors said was historically conducive to human settlement and habitation.
That would happen if global temperatures rise an average of 4.9 degrees Fahrenheit, or 2.7 degrees Celsius, the estimate if current policies are held in place. But if the world adheres to the U.N. goal of temperature rise, of 1.5 degrees Celsius, it would spare more than 1.5 billion people by 2070, keeping those exposed to the most dangerous heat at about 4.4 percent of the world’s estimated population by that year.
“Our study highlights the phenomenal human cost of failing to tackle the climate emergency,” Tim Lenton, the lead author and the director of the Global Systems Institute at the University of Exeter, said in a statement.
“For every 0.1°C of warming above present levels, about 140 million more people will be exposed to dangerous heat. This reveals both the scale of the problem and the importance of decisive action to reduce carbon emissions,” he said.
The study was published Monday in the Nature Sustainability journal.
The most dangerously hot countries by 2070
India, Nigeria and Indonesia were the countries with the largest populations at risk if temperatures rise 4.9 degrees Fahrenheit.
The authors also looked at the countries with the largest exposure to the most extreme temperatures by the percentage of landmass. By that measure, Burkina Faso, Mali and Qatar face the worst consequences from the extreme heat — no part of their territories will be at safe temperatures.
Some countries that face dire consequences with a rise in temperature of 4.9 degrees Fahrenheit would be far better off if the world holds to its tighter, U.N.-backed climate goals. In the Philippines, for example, 86 million people would live in extreme areas under the higher warming scenario, a number that drops to 186,000 if the world holds to the U.N. goals.
The study’s authors said they wanted to focus more attention on the human impact of global warming, arguing that many projections assign greater weight to the economic effects of climate change. That leads to giving greater weight to the populations of rich nations, they said.
Average temperatures beyond 84 degrees Fahrenheit have been linked to increased mortality, decreased labor productivity, more dangerous pregnancies, decreased crop yields, and greater conflict and disease, Chi Xu, an ecologist at Nanjing University who was an author of the study, said in a statement.
The study said that human population density has historically clustered around two peaks of temperatures: a primary one of an average annual temperature of about 55 degrees Fahrenheit, and another around 81 degrees Fahrenheit. Pushing beyond that higher level quickly becomes hazardous, they said.