Nearly 3.8 billion people could face extreme heat by 2050 and while tropical countries will bear the brunt cooler regions will also need to adapt, scientists said yesterday.

Demand for cooling will “drastically” increase in giant countries like Brazil, Indonesia and Nigeria, where hundreds of millions of people lack air conditioning or other means of beating the heat.

But even a moderate increase in hotter days could have a “severe impact” in nations not used to such conditions like Canada, Russia and Finland, said scientists from the University of Oxford.