The world is on track to add nearly two months of dangerous super-hot days each year by the end of the century, with poorer small nations hit far more often than the biggest carbon-polluting countries, a study released Thursday found.

But efforts to curb emissions of heat-trapping gases that started 10 years ago with the Paris climate agreement have had a significant effect. Without them Earth would be heading to an additional 114 days a year of those deadly extra hot days, the same study found.

The international collection of climate scientists World Weather Attribution and the U.S.-based Climate Central teamed up to use computer simulations to calculate just how much of a difference the landmark accord has made in terms of one of the biggest climate effects on people: heat waves.

The report — which is not yet peer-reviewed but uses established techniques for climate attribution —calculated how many super-hot days the world and more than 200 countries got in 2015, how many Earth gets now and what's projected in two future scenarios.

One scenario is if countries fulfill their promises to curb emissions and by the year 2100 the world warms 2.6 degrees Celsius (4.7 degrees Fahrenheit) above pre-industrial times. That adds 57 super-hot days to what Earth gets now, according to the study. The other scenario is the 4 degrees Celsius (7.2 degrees Fahrenheit) of warming that the world had been on track to hit before the Paris agreement. The study found that would double the number of added hot days.

“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 super-hot 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 super-hot days on average, the report 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.

Thursday's study calculated that the week-long southern Europe heat wave in 2023 is now 70% more likely and 0.6 degrees Celsius (1.1 degrees Fahrenheit) 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 degrees Celsius (5.4 degrees Fahrenheit) 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 affects of climate change seem, even under the less extreme of the two scenarios. The scientists broke down how many extra super-hot days are expected for each country by the end of the century under that scenario.

The ten 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 super-hot 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 super-hot days.

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

Hawaii and Florida are the U.S. states that will see the biggest increase in super hot 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.”

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