If global warming continues unchecked, the heat that’s coming later this century in some parts of the world will bring “nearly unlivable” conditions for up to 3 billion people, a study released Monday said.

The authors predict that by 2070,  much of the world’s population is likely to live in climate conditions that are “warmer than conditions deemed suitable for human life to flourish.”

The study warned that unless greenhouse gas emissions are curtailed, average annual temperatures will rise beyond the climate “niche” in which humans have thrived for 6,000 years.

That “niche” is equivalent to average yearly temperatures of roughly 52 to 59 Fahrenheit. The researchers found that people, despite all forms of innovations and migrations, have mostly lived in these climate conditions for several thousand years.

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“We show that in a business-as-usual climate change scenario, the geographical position of this temperature niche is projected to shift more over the coming 50 years than it has moved (in the past 6,000 years),” the study warned.

Read more: USA TODAY