WASHINGTON (AP) — A recent study reveals that the planet is on course to experience nearly two extra months of perilously hot days annually by the century’s end, with smaller, poorer nations bearing the brunt more than the major carbon-emitting countries.

However, efforts initiated a decade ago to reduce greenhouse gas emissions through the Paris climate agreement have made a notable impact. Without these measures, the planet would be facing 114 more days of these extreme heat conditions each year, as indicated by the study.

The global team of climate experts from World Weather Attribution and Climate Central, based in the U.S., collaborated to employ computer models to assess the significant role the landmark agreement has played in mitigating one of the most direct climate impacts on human populations: heat waves.

This report, which hasn’t yet undergone peer review but relies on well-established climate attribution methods, assessed the number of extremely hot days worldwide and for over 200 countries in 2015, the present day, and projections under two future scenarios.

One scenario considers nations meeting their emission reduction targets, leading to a 2.6 Celsius (4.7 Fahrenheit) rise above preindustrial levels by 2100. This would result in 57 more superhot days than the current situation. The alternative scenario predicts a 4 Celsius (7.2 Fahrenheit) increase, the trajectory before the Paris accord, which would double the additional hot days, according to the study.

Pain and suffering coming

“There will be pain and suffering because of climate change,” said Climate Central Vice President for Science Kristina Dahl, a report co-author. “But if you look at this difference between 4 degrees C of warming and 2.6 degrees C of warming, that reflects the last 10 years and the ambitions that people have put forth. And to me, that’s encouraging.”

The study defines superhot days for each location as days that are warmer than 90% of the comparable dates between 1991 and 2020. Since 2015, the world has already added 11 superhot days on average, the report said.

“That heat sends people to the emergency room. Heat kills people,” Dahl said.

The report doesn’t say how many people will be affected by the additional dangerously hot days, but co-author Friederike Otto of Imperial College London said that “it will definitely be tens of thousands or millions, not less.” She noted that thousands die in heat waves each year already.

Imagine recent heat waves but worse

Thursday’s study calculated that the weeklong southern Europe heat wave in 2023 is now 70% more likely and 0.6 C (1.1 F) warmer than it would have been 10 years ago when the Paris agreement was signed. And if the world’s climate-fighting efforts don’t increase, a similar heat wave at the end of the century could be 3 C (5.4 F) hotter, the report estimated.

A heat wave similar to last year’s Southwestern United States and Mexico heat wave could be 1.7 degrees Celsius (3.1 degrees Fahrenheit) hotter by the end of the century under the current carbon pollution trajectory, the report said.

Other groups are also finding more than hundreds of thousands of deaths from recent heat waves in peer-reviewed research with much of it because of human-caused climate change, said University of Washington public health and climate scientist Kristie Ebi, who wasn’t part of Thursday’s report.

More than anything, the data shows how unfair the effects of climate change seem, even under the less extreme of the two scenarios. The scientists broke down how many extra superhot days are expected for each country by the end of the century under that scenario.

Country data shows high heat inequality

The 10 countries that will see the biggest increases in those dangerous heat days are nearly all small and dependent on the ocean, including the Solomon Islands, Samoa, Panama and Indonesia. Panama, for example, can expect 149 extra superhot days. Altogether the top 10 of those countries produced only 1% of the heat-trapping gases now in the air but will get nearly 13% of the additional superhot days.

But top carbon polluting countries, the United States, China and India are predicted to get only between 23 and 30 extra superhot days. They are responsible for 42% of the carbon dioxide in the air, but are getting less than 1% of the additional superhot days.

“This report beautifully and tangibly quantifies what we’ve been saying for decades. The impacts of global warming are going to disproportionally affect developing nations that historically haven’t emitted significant quantities of greenhouse gases,” said University of Victoria climate scientist Andrew Weaver, who wasn’t part of the study team. “Global warming is driving yet another wedge between have and have not nations; this will ultimately sow seeds of further geopolitical instability.”

Hawaii and Florida are the U.S. states that will see the biggest increase in superhot days by the end of the century under the current carbon pollution trajectory, while Idaho will see the smallest jump, the report found.

While the report makes sense, Potsdam Climate Institute Director Johan Rockstrom, who wasn’t part of the research, said people shouldn’t be relieved that we are no longer on the 4-degree warming pre-Paris trajectory because the current track “would still imply a disastrous future for billions of humans on Earth.”