A new study examines the human cost of global warming and the dangers it will entail by 2110, warning that certain countries face a catastrophic fate.
The study warned that current policies to curb global warming will expose more than a fifth of humanity to extreme and life-threatening heat by the end of the century.
Earth's surface temperatures are set to rise by 2.7°C by 2100 compared to the pre-industrial era.
This is expected to affect more than two billion people — or 22 percent of the world's population by that time, taking them away from the comfortable climatic conditions that have allowed humanity to evolve over thousands of years, according to the study published in Nature Sustainability.
Fatal heat
India, Nigeria and Indonesia have the largest number of people who could face deadly heat under this scenario, numbering 600 million, 300 million and 100 million, respectively.
Lead author Tim Linton, from the University of Exeter, said: "It would represent a profound reshaping of the habitability of the planet's surface, which could lead to a large-scale reorganisation of where people live.
But by putting a limit on warming at 1.5°C, the most ambitious goal of the 2015 Paris Agreement, the number of people at risk is reduced to less than half a billion.
The world is currently experiencing a temperature rise of about 1.2 degrees Celsius as a result of human activity, especially for the use of fossil fuels (coal, oil and gas), with a series of disasters such as heat waves, droughts and forest fires.
Failure bill
"The costs of climate change are often expressed in financial terms, but our study highlights the enormous human cost of failing to address the climate emergency," said Tim Linton.
"For every 0.1°C rise above current levels, an additional 140 million people will be exposed to dangerous heat waves."
The "dangerous heat" threshold in the study was set at 29 degrees Celsius as the average annual temperature.
The risks are increasing in areas along the equator. The climate can become deadly if temperatures rise, due to humidity that prevents the human body from cooling itself by sweating.