New research on climate change demonstrates that a large swath of the African continent would become dangerously hot with a projected 2.7°C global temperature rise, including more than 300 million people in Nigeria—the most vulnerable nation, after India, if efforts to limit warming to 1.5°C fail.

Sudan, Niger and Burkina Faso fall into the list of Top 10 nations with exposed populations if temperatures range beyond what the international research team, led by Dr. Timothy Lenton at the University of Exeter, identify as the “human climate niche” in which people and communities can thrive. Their work was published this week in the journal Nature Sustainability.

The future populations of Mali, Ghana, Benin and Chad aren’t far behind. In terms of the percentage of affected land mass—the geography rather than population—it’s Burkina Faso and Mali who have the greatest exposure in the world. Benin, Gambia, Niger, Senegal, Mauritania and Djibouti also fall within the Top 15 affected nations.

Lenton says that for every 0.1°C of warming above present levels, about 140 million more people will be exposed to dangerous heat, many of them in the least developed countries.

“What is the human cost of climate change and who bears it? Existing estimates tend to be expressed in monetary terms, tend to recognize impacts on the rich more than those on the poor (because the rich have more money to lose) and tend to value those living now over those living in the future (because future damages are subject to economic discounting),” the authors said.

“From an equity standpoint, this is unethical—when life or health are at stake, all people should be considered equal, whether rich or poor, alive or yet to be born.”