One in five people could live in dangerously hot conditions by the end of the century if global warming continues at its current pace, even if nations uphold their pledges under the Paris Agreement, scientists warned in a new peer-reviewed study. It’s the latest research published in recent days that points to the stark human and societal costs of the accelerating climate crisis as global carbon emissions continue to rise to unprecedented levels.

The study, published Monday in the journal Nature Sustainability, estimates that some 2 billion people would see a mean annual temperature of 84 degrees Fahrenheit or higher, starting in as early as 2070, when Earth’s population is expected to reach at least 9.5 billion. Most people live in a “human climate niche” that ranges between a mean annual temperature of 55 degrees and 80 degrees, the researchers said, so that many people experiencing a major uptick in regional heat would be unprecedented.

Such a temperature threshold, where 84 degrees or higher becomes the middle ground for the year, can also be very dangerous for anyone without air conditioning or other means to cool off, the study’s authors also noted. According to their estimate, some of the nations that will be hardest hit by the heat are also home to some of the world’s poorest communities, where air conditioning typically isn’t an option.

Of the estimated 2 billion people that could be forced out of their climate niche and into dangerous extreme heat, the study found, 600 million will be in India, 300 million in Nigeria and 100 million in Indonesia.

“Those people who are affected are the poorer people on the planet,” Tim Lenton, director of the Global Systems Institute at Exeter and the study’s lead author, told Forbes. “At higher temperatures, life becomes unbearable, affecting water, agriculture and food. You can’t barricade yourself from climate change. There is an undeniable interconnection amongst nations.”