2024 was the hottest year on record, the World Meteorological Organization said on Thursday, and the first in which temperatures exceeded 1.5C above pre-industrial times - a threshold that may lead to more severe climate disasters.
The latest bleak assessment of the state of climate change comes as the death toll from wildfires raging in California climbs at the start of the new year.
The WMO and the European Union's Copernicus Climate Change Service (C3S) said climate change was pushing the planet's temperature to levels never before experienced by modern humans.
"Today’s assessment from the World Meteorological Organization is clear: 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 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 have all been in the top 10 hottest years on record, according to the World Meteorological Organization.
"The trajectory is just incredible," C3S director Carlo Buontempo told Reuters, noting that every month in 2024 was the warmest or second-warmest for that month since records began.
Wildfires are one of the many disasters that climate change is making more frequent and severe. The fires raging in Los Angeles this week have killed at least 10 people and devoured nearly 10,000 structures.
But while the impacts of climate change now affect people from the richest to the poorest on earth, political will to address it has waned in some countries.
US President-elect Donald Trump, who takes office on Jan. 20, has called climate change a hoax, despite the global scientific consensus that it is caused by humans.
Matthew Jones, a climate scientist at the University of East Anglia in Britain, said fire-prone weather such as that affecting California will keep increasing "so long as progress on tackling the root causes of climate change remains sluggish".
The main cause of climate change is CO2 emissions from burning fossil fuels.
Recent European elections have also shifted political priorities towards industrial competitiveness, with some European Union governments seeking to weaken climate policies they say hurt business.
EU climate commissioner Wopke Hoekstra said the 1.5C 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 1.5C 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 1.5C, while estimating a slightly lower average temperature of 1.53C for the year.
Governments promised under the 2015 Paris Agreement to try to prevent the average temperature rise exceeding 1.5C.
Although 2024 does not breach that target -- which measures the longer-term average temperature -- Buontempo said rising greenhouse gas emissions meant the world was on track to soon blow past the Paris goal.
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.
In 2024, Bolivia and Venezuela suffered disastrous fires, while torrential floods hit Nepal, Sudan and Spain, and heat waves in Mexico killed thousands.
Climate change is worsening storms and torrential rainfall, because a hotter atmosphere can hold more water, leading to intense downpours. The amount of water vapor in the planet's atmosphere reached a record high in 2024.
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 US non-profit Berkeley Earth, said he expected 2025 to be among the hottest years on record, but likely not top the rankings. That's because temperatures in early 2024 got an extra boost from El Niño, a warming weather pattern which is now trending towards its cooler La Nina counterpart.
"It's still going to be in the top three warmest years," he said.
