Most days could be dangerously hot for 5 billion people by 2100

James Dinneen is a writer.

With 3C of global warming by the end of the century, more than 5 billion people could be exposed to dangerous heat and humidity.

The heat index, a measure of relative humidity and air temperature, is considered to be a dangerous measure of heat for humans. Those with a heat index above 51C can cause heat stroke and death, while those with a heat index below 51C can cause heat exhaustion.

By the end of the century, a range of greenhouse gas emissions scenarios were modeled by Lucas and his colleagues. The global average temperature will rise between 2.1 and 4.3C by the end of the century.

Future daily weather was assumed to be similar to past patterns. We expect Junes to be the same as they have been for the past two decades. It's just a tad hotter. It's more humid in some places.

By the end of the century, tropical and subtropical regions will experience dangerously hot days for a quarter to half of each year, and for most of the year. 5.3 billion people in India, Africa, and the Arabian peninsula would be exposed to extremely dangerous heat on 15 or more days a year by the year 2200.

Between 15 and 90 days of dangerous heat can be seen in places far away from the equator. A detailed look at Chicago, where a rare 1995 heatwave killed around 500 people, shows that it could become an annual event.

The findings are alarming and the best way to avoid the effects of extreme heat is to stop emissions. Reliable air conditioning is one of the needed adaptions.

People need to understand that heat kills. It doesn't have to.

Nature Communications Earth and Environment was published in the journal.