Billions projected to suffer nearly unlivable heat in 2070

KENSINGTON, Maryland (AP) — In just 50 years, 2 billion to 3.5 billion people, mostly the poor who can’t afford air conditioning, will be living in a climate that historically has been too hot to handle, a new study said.

With every 1.8 degree (1 degree Celsius) increase in global average annual temperature from man-made climate change, about a billion or so people will end up in areas too warm day-in, day-out to be habitable without cooling technology, according to ecologist Marten Scheffer of Wageningen University in the Netherlands, co-author of the study.

How many people will end up at risk depends on how much heat-trapping carbon dioxide emissions are reduced and how fast the world population grows.

Under the worst-case scenarios for population growth and for carbon pollution — which many climate scientists say is looking less likely these days — the study in Monday’s journal Proceedings of the National Academy of Sciences predicts about 3.5 billion people will live in extremely hot areas. That’s a third of the projected 2070 population.

But even scenarios considered more likely and less severe project that in 50 years a couple of billion people will be living in places too hot without air conditioning, the study said.

“It’s a huge amount and it’s a short-time. This is why we’re worried,’’ said Cornell University climate scientist Natalie Mahowald, who wasn’t part of the study. She and other outside scientists said the new study makes sense and conveys the urgency of the man-made climate change differently than past research.

In an unusual way to look at climate change, a team of international scientists studied humans like they do bears, birds and bees to find the “climate niche” where people and civilizations flourish. They looked back 6,000 years to come up with a sweet spot...