Climate change will hit more fiercely and quicker than expected, according to a new study from the Proceedings of the National Academy of Sciences, or PNAS. More than one billion people, and up to one-third of the world’s total population, could live in “insufferable heat” within 50 years. The study concluded that if emissions continue to worsen, areas where one-third of humanity lives will become as hot as the Sahara Desert.

The study approaches climate change from a unique angle. Instead of focusing on economic impacts or raw data as it applies to the planet as a whole, the authors instead looked at how warming temperatures could impact specific human habitat. India, for example, could have 1.2 billion people living in temperatures too hot for comfort, and 485 million Nigerians could face the same predicament.

“The numbers are flabbergasting. I literally did a double take when I first saw them, ” said Tim Lenton of Exeter University, one of the study’s authors, to The Guardian. “I’ve previously studied climate tipping points, which are usually considered apocalyptic. But this hit home harder. This puts the threat in very human terms.”

If these models were to come to fruition, the world would likely see mass migration and immense strain on its food systems. Given that future population growth is expected to center around areas of the world that are already particularly warm — parts of Africa and Asia — the percent of people living outside the “comfortable” zone with average temperatures between 43 and 82 degrees Fahrenheit is expected to increase. To slow the warming trend and avoid catastrophe, mankind needs to reduce dependence on fossil fuels and undergo massive efforts to remove greenhouse gases from the atmosphere.