Dangerous heat waves to at least triple across the world by 2100, study says

ATLANTA — The dangerous levels of heat that have scorched swathes of the northern hemisphere this summer are likely to hit most of the world between three and 10 times more often by the turn of the century, as the impacts of the human-caused climate crisis accelerate, a new study has found.

That increase is projected to happen in mid-latitude countries, like the U.S., China, Japan and those in Western Europe, according to the study, published in Communications Earth & Environment on Thursday by researchers at Harvard University and the University of Washington. "Dangerous heat" is defined as 103 degrees Fahrenheit and above.

By 2050, the number of days of dangerous heat in this region will more than double.

Deadly heat waves are currently rare in the mid-latitudes, but they are likely to start happening annually in this region. Chicago, for example, is projected to see a 16-fold increase in dangerous heatwaves by 2100, the study shows.

The situation will be even worse in the tropics, where people could be exposed to dangerous heat most days of the year. Days of "extremely dangerous heat" — which is defined as 124 Fahrenheit (51 Celsius) — could double. Experts say those levels of heat push the limits of human survivability.

The projections were made under the assumption that average global temperatures will rise by 3.6 Fahrenheit (two degrees Celsius), a cap set out in the 2015 Paris Agreement. The agreement says that a lower goal of 2.7 Fahrenheit (1.5 Celsius) of warming is preferable, and there is growing momentum for the world to keep to 1.5 Celsius by making deeper and quicker cuts to greenhouse gas emissions.

"The record-breaking heat events of recent summers will become much more common in places like North America and Europe," said lead author Lucas Vargas Zeppetello from Harvard University in a press release. "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."

The study used the heat index, which considers both air temperature and humidity to measure the impact on heat on humans.

"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 world's nations agreed at international climate talks in Glasgow, Scotland, last year to come to this year's talks in Egypt with emissions reductions plans that align with the Paris Agreement. Several countries have missed deadlines to submit their updated plans.

The authors of the study said the world must find ways to adapt to the changing levels of heat to avoid a spike in illnesses, especially among elderly people, those who work outdoor and those with lower incomes.

Several European countries are poorly set up to deal with extreme heat. In the U.K., for example, few people have air conditioning, trains were canceled and an airport runway melted during a days-long heat wave, where temperatures surpassed 104 Fahrenheit (40 Celsius) for the first time on record.

The study looked at predictions from existing global climate models, projections for human population increases, and the relationship between economic growth and carbon emissions to establish how much and how quickly temperatures were expected to rise.

They also estimated that there was only a 0.1% chance of limiting warming to 1.5 Celsius by 2100 and that the world will likely approach 3.6 Fahrenheit (2 Celsius) of warming as soon as 2050. Many countries and businesses are aiming to achieve net zero — where greenhouse gas emissions are no greater than those removed from the atmosphere — by that same year.

"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."

Related topics