It was also the first time the three-year temperature average broke through the threshold set in the 2015 Paris Agreement of limiting warming to no more than 1.5C since pre-industrial times.
Experts say that keeping the earth below that limit could save lives and prevent catastrophic environmental destruction around the globe.
The analysis from World Weather Attribution researchers, came after a year when people around the world were slammed by the dangerous extremes brought on by a warming planet.
Temperatures remained high despite the presence of a La Nina, the occasional natural cooling of Pacific Ocean waters that influences weather worldwide.
Researchers cited the continued burning of fossil fuels - oil, gas and coal - that send planet-warming greenhouse gases into the atmosphere.
"If we don't stop burning fossil fuels very, very, quickly, very soon, it will be very hard to keep that goal" of limiting warming, Friederike Otto, co-founder of World Weather Attribution and an Imperial College London climate scientist, told The Associated Press. "The science is increasingly clear."
Extreme weather events kill thousands of people and cost billions of dollars in damage annually.
WWA scientists identified 157 extreme weather events as most severe in 2025, meaning they met criteria such as causing more than 100 deaths, affecting more than half an area's population or having a state of emergency declared. Of those, they closely analysed 22.
That included dangerous heatwaves, which the WWA said were the world's deadliest extreme weather events in 2025.
The researchers said some of the heatwaves they studied in 2025 were 10 times more likely than they would have been a decade ago due to climate change.
"The heatwaves we have observed this year are quite common events in our climate today, but they would have been almost impossible to occur without human-induced climate change," Otto said. "It makes a huge difference."
Meanwhile, prolonged drought contributed to wildfires that scorched Greece and Turkey. Torrential rains and flooding in Mexico killed dozens of people and left many more missing. Super Typhoon Fung-wong slammed the Philippines, forcing more than a million people to evacuate. Monsoon rains battered India with floods and landslides.
The WWA said the increasingly frequent and severe extremes threatened the ability of millions of people across the globe to respond and adapt to those events with enough warning, time and resources, what the scientists call "limits of adaptation."
This year's United Nations climate talks in Brazil in November ended without any explicit plan to transition away from fossil fuels, and though more money was pledged to help countries adapt to climate change, they will take more time to do it.
Officials, scientists, and analysts have conceded that Earth's warming will overshoot 1.5C, though some say reversing that trend remains possible.
Andrew Kruczkiewicz, a senior researcher at the Columbia University Climate School who wasn't involved in the WWA work, said places are seeing disasters they aren't used to, extreme events are intensifying faster and they are becoming more complex.
That requires earlier warnings and new approaches to response and recovery, he said.
"On a global scale, progress is being made," he added, "but we must do more."
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