Deadly heat to surge by 2100, even with emissions reductions: study

Much of the world will face a significant uptick in deadly heat waves by the end of the century, even if countries manage to meet their agreed-upon emission reduction goals, a new study has found.

Such heat events will be three to 10 times more common in 2100 than they are today in the U.S., Western Europe, China and Japan, regardless of efforts to keep global warming below 2 degrees Celsius (3.6 degrees Fahrenheit), according to the study, published in Communications Earth & Environment on Thursday.

As part of the Paris climate agreement that was signed at the 2015 United Nations Climate Change Conference, participating countries agreed to adhere to this limit, with hopes of keeping the increase to an even smaller 1.5 degrees Celsius (2.7 degrees Fahrenheit).

To improve their chance of success, each nation submitted its own climate action plan to cut greenhouse gas emissions. But the authors of Thursday’s study fear that these efforts will be insufficient to drive down heat.

“The record-breaking heat events of recent summers will become much more common in places like North America and Europe,” lead author Lucas Vargas Zeppetello, a doctoral student at the University of Washington at the time of the study, said in a statement.

“For many places close to the equator, by 2100 more than half the year will be a challenge to work outside, even if we begin to curb emissions,” added Vargas Zeppetello, who is now a postdoctoral researcher at Harvard University.

Vargas Zeppetello and his colleagues evaluated projections for the future “heat index,” a combination of air temperature and humidity that measures the impact of heat on the human body.

A “dangerous” heat index is defined by the National Weather Service as 103 degrees Fahrenheit, the authors explained. Meanwhile, an “extremely dangerous” heat index is 124 degrees Fahrenheit and is considered unsafe to humans for any amount of time.

“These standards were first created for people working indoors in places like boiler rooms — they were not thought of as conditions that would happen in outdoor, ambient environments. But we are seeing them now,” Vargas Zeppetello said.

The scientists said they used a probability-based method to calculate a range of future possible scenarios, by combining historical data with population projections, economic growth and carbon intensity.

They observed that even if countries met their Paris agreement commitments, the U.S., Western Europe, China and Japan would cross the “dangerous” heat index threshold three to 10 more times than they do today by the end of the century.

In this same scenario, the tropics could see their “dangerous” days double — covering half the year, according to the study.

And in a worst-case circumstance — a scenario in which emissions remain unchecked until 2100 — “extremely dangerous” conditions could become common in countries near the equator, such those in sub-Saharan Africa and in India, the authors determined.

“These are frightening scenarios that we still have the capacity to prevent,” Vargas Zeppetello said. “This study shows you the abyss, but it also shows you that we have some agency to prevent these scenarios from happening.”