By the end of the century, nearly 2 billion people could live with average annual temperatures warmer than 84 degrees Fahrenheit, or 29 degrees Celsius, the maximum level that 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 kept in place. But if the world meets the UN’s 1.5 degree Celsius temperature rise target, 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 before that year.
“Our study highlights the phenomenal human cost of failing to tackle the climate crisis,” Tim Lenton, the lead author and director of the Global Systems Institute at the University of Exeter, said in a statement.
“For every 0.1°C of warming above current levels, around 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 CO2 emissions,” he said .
The study was published Monday in the journal Nature Sustainability.
The most dangerous countries in 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 greatest exposure to the most extreme temperatures as a percentage of land mass. By that measure, Burkina Faso, Mali and Qatar face the worst consequences of the extreme heat – no part of their territories will have safe temperatures.
Some countries facing dire consequences with a temperature increase of 4.9 degrees Fahrenheit would be far better off if the world sticks to its tighter, UN-backed climate goals. In the Philippines, for example, 86 million people would live in extreme areas under the higher-warming scenario, a figure that drops to 186,000 if the world sticks to UN targets.
The study’s authors said they wanted to focus more attention on the human impact of global warming, arguing that many projections give more weight to the economic effects of climate change. That leads to giving greater weight to the populations of rich nations, they said.
Average temperatures above 84 degrees Fahrenheit have been linked to increased mortality, reduced labor productivity, more dangerous pregnancies, reduced crop yields and greater conflict and disease, Chi Xu, an ecologist at Nanjing University who authored the study, said in a statement.
The study said human population density has historically clustered around two temperature peaks: one primary with an average annual temperature of about 55 degrees Fahrenheit and another around 81 degrees Fahrenheit. Pushing beyond that higher level quickly becomes dangerous, they said.
