Last year was the third-hottest on record, scientists have said, with mounting fossil fuel pollution behind “exceptional” temperatures.

The EU’s Copernicus climate agency said 2025 had been marginally cooler than 2023 at the end of a scorching three-year run during which surface air temperatures averaged 1.52C above pre-industrial levels.

Current rates of heating could breach the Paris agreement limit of 1.5C (2.7F) – which is measured over 30 years to iron out natural fluctuations – before the end of the decade, according to Copernicus. That is more than 10 years sooner than scientists expected when world leaders signed the pledge in 2015.

“We are bound to pass it,” said Carlo Buontempo, the director of the Copernicus climate change service. “The choice we now have is how to best manage the inevitable overshoot and its consequences.”

The data published on Wednesday is based on the re-analysis of billions of weather measurements from satellites, ships, aircraft and weather stations. It was separately compiled by several organisations who monitor the global climate in Europe and the US, with minor variations in their results.

Copernicus’s ERA5 dataset showed 2025 was 1.47C hotter than the pre-industrial period, when the large-scale destruction of nature and burning of coal, oil and gas began in earnest, while the UK Met Office’s HadCRUT5 dataset pegged it slightly lower at 1.41C.

The hottest year on record since the mid-19th century is 2024, which was plagued by heatwaves and wildfires. The Met Office said natural variation and reductions in heat-masking aerosol pollutants have made the last three years extra hot.

Tim Osborn, the director of the University of East Anglia’s climate research unit, which worked with the Met Office to produce the data, said a natural weather pattern in the Pacific known as El Niño added about 0.1C to global temperatures in 2023 and 2024, which contributed to the “abrupt onset of the recent temperature surge”.

Visitors to the Sensoji temple in Tokyo take advantage of a cooling mist during a heatwave in August 2025. Photograph: Issei Kato/Reuters

“This natural influence weakened by 2025,” he said. “And therefore the global temperature we observed in 2025 provides a clearer picture of the underlying warming.”

Copernicus said the first month of 2025 was the hottest January on record, while March, April and May were each the second-warmest for that time of year. Each month except February and December was warmer than the corresponding month in any year before 2023, the scientists found.

The unnatural heat is largely the result of a blanket of carbon pollution smothering the Earth, worsening most weather extremes and jeopardising the stable conditions in which humanity has thrived.

Copernicus found temperatures over the tropical Atlantic and Indian Ocean were less extreme in 2025 than in 2024, but these were offset partly by higher temperatures at the poles. Antarctica recorded its hottest year, and the Arctic its second-hottest.

Polar sea ice cover fell to its lowest level since satellite observations began in the 1970s in February. Over the year as a whole, half of the planet’s land experienced more days than average with at least “strong” heat stress, when temperatures feel above 32C.

Berkeley Earth, a US non-profit that calculated 1.44C of warming for 2025, estimates that 8.5% of the world’s population live in areas that had record high annual average temperatures last year. Its scientists said similar heat was likely in 2026.

Bill McGuire, an emeritus professor of climate hazards at University College London, who was not involved in the analysis, said the findings were “grim but far from unexpected tidings”.

“To all intents and purposes, the 1.5C limit is now dead in the water,” he said. “Whichever way you look at it, dangerous climate breakdown has arrived, but with little sign that the world is prepared or even paying serious attention.”

Global emissions have continued to rise 10 years after the Paris agreement was signed, despite a boom in renewable energy and regional successes in cleaning up dirty economies.

Laurence Rouil, the director of the Copernicus atmosphere monitoring service, said the data for 2025 painted a clear picture that showed human activity was still the dominant driver of exceptional temperatures.

“The atmosphere is sending us a message,” she said. “And we must listen.”