A new study warns that up to three billion people could be living in areas that are too hot for humans within 50 years.

Humans tend to live within a narrow “climate niche” with ideal average temperatures to grow food, keep livestock and create a flourishing society.

Most of the world's population lives within a mean annual temperature of between 11℃ and 15℃.

A smaller band of between 20℃ to 25℃ encompasses areas in South Asia that are affected by the Indian monsoon - the annual rains that irrigates large swathes of cropland vital for food production.

“As an archaeologist I always tell my students that our technology, our minds, and our cumulative culture have enabled us to live anywhere,’ says Tim Kohler, an archaeologist at the University of Washington and co-author of the study.

“That's true of course. But it turns out that there is a distinct climate zone in which our numbers are greatest, and within which we have also been most economically productive.”

The new research finds that for every 1℃ of warming, one billion people will either have to migrate to cooler regions or adapt to extreme heat conditions.

Dr Kohler says the findings are based on a “business-as-usual” scenario, or; “What could happen if we don't change our ways”.

The Earth is currently on track for 3℃ of warming by 2100. The study suggests that because land areas are warming faster than the oceans, temperatures experienced by humans are likely to rise by about 7.5℃ by 2070.

This means that the temperature experienced by an average person will change more in the coming decades than it has over the past 6,000 years.

This could have severe consequences for food production, access to water sources, conflict and disruption caused by migration.

“It's reasonable to conclude that if something has been reasonably stable for 6000 years, we're not going to change it painlessly or quickly,” Mr Kohler said.

Currently, ‘extreme’ conditions (annual mean temperatures above 29℃) cover 0.8 per cent of the earth's land area.

But those extreme heat areas are expected to spread to 19 per cent of the Earth's surface, affecting 3.5 billion people by 2070.