Last year was the warmest on record, the first to breach a symbolic threshold, and brought with it deadly impacts like flooding and drought, scientists have said.
Two new datasets found 2024 was the first calendar year when average global temperatures exceeded 1.5C above pre-industrial levels - before humans started burning fossil fuels at scale.
The record heat has not only has real-world implications, as it contributed to deadly flooding in Spain and vicious drought in places like Zambia in southern Africa.
It is also highly symbolic.
Countries agreed in the landmark Paris Agreement to limit warming ideally to 1.5C, because after that the impacts would be much more dangerous.
The news arrives as California battles "hell on earth" wildfires, suspected to have been exacerbated by climate change.
And it comes as experts warn support for the Paris goals is "more fragile than ever" - with Donald Trump and the Argentinian president poised to row back on climate action.
What caused 2024 record heat - and is it here to stay?
Friends of the Earth called today's findings from both the EU's Copernicus Climate Change service and the Met Office "deeply disturbing".
The "primary driver" of heat in the last two years was climate change from human activity, but the temporary El Nino weather phenomenon also contributed, they said.
The breach in 2024 does not mean the world has forever passed 1.5C of warming - as that would only be declared after several years of doing so, and warming may slightly ease this year as El Nino has faded.
But the world is "teetering on the edge" of doing so, Copernicus said.
Prof Piers Forster, chair of the UK's Climate Change Committee, called it a "foretaste of life at 1.5C".
Dr Gabriel Pollen, Zambia's national coordinator for disasters, said "no area of life and the economy is untouched" by the country's worst drought in more than 100 years.
Six million people face starvation, critical hydropower has plummeted, blackouts are frequent, industry is "decimated", and growth has halved, he said.
Paris goal 'not obsolete'
Scientists were at pains to point out it is not too late to curb worse climate change, urging leaders to maintain and step up climate action.
Professor Forster said temporarily breaching 1.5C "does not mean the goal is obsolete", but that we should "double down" on slashing greenhouse gas emissions and on adapting to a hotter world.
The Met Office said "every fraction of a degree" still makes a difference to the severity of extreme weather.
Copernicus director Carlo Buontempo added: "The future is in our hands: swift and decisive action can still alter the trajectory of our future climate".
Climate action is 'economic opportunity'
Copernicus found that global temperatures in 2024 averaged 15.10°C, the hottest in records going back to 1850, making it 1.60°C above the pre-industrial level during 1850-1900.
The Met Office's data found 2024 was 1.53C above pre-industrial levels.
The figures are global averages, which smooth out extremes from around the world into one number. That is why it still might have felt cold in some parts of the world last year.
Greenpeace campaigner Philip Evans said as "the world's most powerful climate denier" Donald Trump returns to the White House, others must "take up the mantle of global climate leadership".
The UK's climate minister Kerry McCarthy said the UK has been working with other countries to cut global emissions, as well as greening the economy at home.
"Not only is this crucial for our planet, it is the economic opportunity of the 21st century... tackling the climate crisis while creating new jobs, delivering energy security and attracting new investment into the UK."
(c) Sky News 2025: 'The future is in our hands' scientists say, as 2024 becomes first year to pass 1.5C
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