Levels of the most significant planet-warming gas in our atmosphere rose more quickly than ever previously recorded last year, scientists say, leaving a key global climate target hanging by a thread.
Concentrations of carbon dioxide (CO2) are now more than 50% higher than before humans started burning large amounts of fossil fuels.
Last year, fossil fuel emissions were at record highs, while the natural world struggled to absorb as much CO2 due to factors including wildfires and drought, so more accumulated in the atmosphere.
The rapid increase in CO2 is “incompatible” with the international pledge to try to limit global warming to 1.5C above pre-industrial levels, the Met Office says.

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Most of us know that to live a long and healthy life, we should eat well, exercise and look after our mental health. But working out which steps will bring the most improvement to our health and wellbeing can be tricky.
It gets especially hard when we are faced with so much conflicting advice. Distinguishing a clever marketing ploy from a science-backed technique that might actually be good for you is no easy task.
But Health Fix, the BBC’s new dedicated health newsletter, is here to help.

More than 100 Reddit communities have banned users from posting links to X in protest at owner Elon Musk’s controversial arm gesture at a rally celebrating Donald Trump’s return to office.
The billionaire twice extended his arm out straight as he thanked the crowd for “making it happen.”
Critics, including some historians, said it was a Nazi salute – Mr Musk has dismissed that, saying comparisons with Hitler were “tired” and “dirty tricks.”
However many Reddit users have been unpersuaded by his response describing his actions as “hateful”, leading the moderators of scores of communities – or subreddits – to stop content being shared on X.
X has not commented but Reddit has stressed there is no sitewide ban on X links, telling the BBC in a statement it “has a longstanding commitment to freedom of speech and freedom of association”.
However the platform relies heavily on community moderation, where unpaid individuals known as Redditors decide what is – and isn’t – allowed to be published on their own corner of the website.
In many instances, those Redditors have reached a different conclusion, deciding Mr Musk’s actions were so offensive that they won’t link to content from their subreddits on X, potentially reducing traffic, engagement and – ultimately – revenue.
The biggest subreddits to have enforced the ban include basketball community r/NBA, which has 15 million members, female-focused community r/TwoXChromosomes, which has 14 million members, and American football community r/NFL, which has 12 million members.
It is worth remembering that subreddits are almost always run by fans – it does not mean that the NFL or NBA organisations are taking a stance against Musk.
The BBC has independently verified that at least 100 subreddits have banned X posts.
Of this number, more than 60 have at least 100,000 members.
But the actual number that have instituted the ban will likely be significantly higher by taking into account smaller subreddits with only a few thousand members.
And there are many more communities discussing a potential blacklisting.