Global heating will drive billions of people out of the "climate niche" in which humanity has flourished for millennia, a study has estimated, exposing them to unprecedented temperatures and extreme weather, according to a media report. The world is on track for 2.7-degree Celsius of heating with current action plans and this would mean 2 billion people experiencing average annual temperatures above 29-degree Celsius by 2030, a level at which very few communities have lived in the past, The Guardian reported.

Up to 1 billion people could choose to migrate to cooler places, the scientists said, although those areas remaining within the climate niche would still experience more frequent heatwaves and droughts. However, urgent action to lower carbon emissions and keep global temperature rise to 1.5 C would cut the number of people pushed outside the climate niche by 80 per cent, to 400 million.

The analysis is the first of its kind and is able to treat every citizen equally, unlike previous economic assessments of the damage of the climate crisis, which have been skewed towards the rich. The idea of climate niches for wild animals and plants is well established but the new study, published in the journal Nature Sustainability, identified the climate conditions in which human societies have thrived.

It found most people lived in places with mean annual temperatures spread around 13 C or 25 C. Conditions outside those are too hot, too cold or too dry and associated with higher death rates, lower food production and lower economic growth, The Guardian reported. Professor Chi Xu at Nanjing University in China, and also part of the research team, said: "Such high temperatures [outside the niche] have been linked to issues including increased mortality, decreased labour productivity, decreased cognitive performance, impaired learning, adverse pregnancy outcomes, decreased crop yield, increased conflict and infectious disease spread."