The World Meteorological Organization (WMO) confirmed the 1.5 degrees Celsius breach, after reviewing data from United States, United Kingdom, Japan and European Union scientists.

"Global heating is a cold, hard fact," United Nations secretary-general António Guterres said in a statement. "There's still time to avoid the worst of climate catastrophe. But leaders must act – now."

The bleak assessment came as wildfires charged by fierce winds swept through Los Angeles, with 10 people dead and nearly 10,000 structures destroyed so far. Wildfires are among the many disasters that climate change is making more frequent and severe.

The EU's Copernicus Climate Change Service (C3S) said climate change was pushing the planet's temperature to levels never before experienced by modern humans. Scientists have linked climate change to greenhouse gas emissions, mainly from burning fossil fuels.

The planet's average temperature in 2024 was 1.6 degrees Celsius higher than in the 1850-1900 pre-industrial period, C3S said. The last 10 years are the 10 hottest years on record, the WMO said.

Climate change is worsening storms and torrential rainfall, because a hotter atmosphere can hold more water, leading to intense downpours. Atmospheric water vapor reached a record high in 2024, and the US National Oceanic and Atmospheric Administration (NOAA) said it was the third-wettest year on record.

In 2024, Bolivia and Venezuela suffered disastrous fires, while torrential floods hit Nepal, Sudan and Spain, and heat waves in Mexico and Saudi Arabia killed thousands. While climate change now affects people from the richest to the poorest on Earth, political will to address it has waned in some countries.

A view of damaged houses after the deadly floods following heavy rainfall along the bank of Kalati River in Bhumidanda village of Panauti municipality in Kavre, Nepal on Oct. 1, 2024. (Reuters/Navesh Chitrakar)

Governments promised under the 2015 Paris Agreement to try to prevent the average global temperature rise from exceeding 1.5 degrees Celsius above pre-industrial levels.

US president-elect Donald Trump, who takes office on Jan. 20, has called climate change a hoax, dismissing the global scientific consensus. During his first term in office he withdrew Washington from the Paris Agreement, and he has vowed to push greater fossil fuel production and roll back President Joe Biden's push toward alternative energy.

Recent European elections have shifted political priorities towards industrial competitiveness, with some EU governments seeking to weaken climate policies they say hurt business.

Matthew Jones, a climate scientist at the University of East Anglia in Britain, said climate-linked disasters will grow more common "so long as progress on tackling the root causes of climate change remains sluggish".

EU climate commissioner Wopke Hoekstra said the 1.5 degrees Celsius breach last year showed climate action must be prioritized.

"It is extremely complicated, in a very difficult geopolitical setting, but we don't have an alternative," he told Reuters.

The 1.5 degrees Celsius milestone should serve as "a rude awakening to key political actors to get their act together," said Chukwumerije Okereke, a professor of climate governance at Britain's University of Bristol.

Britain's Met Office confirmed 2024's likely breach of 1.5 degrees Celsius above pre-industrial levels, while estimating a slightly lower average temperature of 1.53 degrees Celsius for the year.

Buontempo noted that 2024 did not breach that target since it measures the longer-term average temperature, but added that rising greenhouse gas emissions put the world on track to blow past the Paris goal soon.

A view of the Weisweiler coal power plant of German utility RWE in Weisweiler, Germany, on Jan. 17, 2023. (Reuters/Wolfgang Rattay)

Countries could still rapidly cut emissions to avoid temperatures from rising further to disastrous levels, he added.

"It's not a done deal. We have the power to change the trajectory," Buontempo said.

Concentrations in the atmosphere of carbon dioxide, the main greenhouse gas, reached a fresh high of 422 parts per million in 2024, C3S said.

Zeke Hausfather, a research scientist at U.S. non-profit Berkeley Earth, said he expected 2025 to be among the hottest years on record, but likely not top the rankings. He noted that temperatures in early 2024 got an extra boost from El Niño, a warming weather pattern now trending toward its cooler La Nina counterpart.

"It's still going to be in the top three warmest years," he said.