Human activity helped make 2025 third-hottest year on record, experts say

Data leads scientists to declare 2015 Paris agreement to keep global heating below 1.5C ‘dead in the water’

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

The World Meteorological Organization (WMO) said 2025 had continued a three-year streak of “extraordinary global temperatures” during which surface air temperatures averaged 1.48C above preindustrial 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 the EU’s Copernicus climate agency. 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 eight datasets published on Wednesday are based on billions of weather measurements from satellites, ships, aircraft and weather stations. They were separately compiled by several organisations that monitor the global climate in Europe, the US, Japan and China, with minor variations in their results.

The WMO’s consolidated analysis found that 2025 was 1.44C hotter than the preindustrial period, when the large-scale destruction of nature and burning of coal, oil and gas began in earnest. Six datasets ranked 2025 as the third hottest year on record, while the other two ranked it as the second hottest.

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 few 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”.

“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 also analysed the temperatures, 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.”

In the US, the National Oceanic and Atmospheric Administration (Noaa) noted that the largest heat anomalies were in Europe, the Arctic, western and southern Asia and parts of Antarctica.

Unlike previous years, there was no media fanfare or public-facing event staged by Noaa and Nasa for their annual temperature reports. Instead, the data was published quietly on their websites on Wednesday morning.

Under Donald Trump, US government agencies have removed or downgraded information on the climate crisis, banned mentions relating to global heating and fired researchers involved in a periodic report, required by Congress, that updates the latest climate science and impacts in the US.

“The Trump administration is not simply refusing to face the reality of climate change we are experiencing, it is actively lying about the science and undermining our nation’s federal scientific resources,” said Dr Carlos Martinez, a senior climate scientist at the Union of Concerned Scientists, a nonprofit advocacy organisation.

“It is acting like there’s no tomorrow by trying to force even more burning of coal, oil and gas, which will cost lives and make the Earth a harder place to live in the years to come.”

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.”

Cover photo:  A firefighter battles to save a home from a wildfire in California in January 2025. Photograph: David McNew/Getty Images