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Hopes of keeping global warming below 1.5°C above pre-industrial levels have been all but extinguished after new data confirmed 2024 was the first calendar year to see average temperatures breach that critical threshold.

Last year was the hottest ever recorded in human history, the World Meteorological Organization (WMO) declared on 10 January, in the latest stark warning that humanity is pushing Earth’s climate into uncharted territory.

The average global temperature for the year exceeded 1.5°C above the pre-industrial baseline for the first time, the agency also confirmed, temporarily breaching the threshold set by the Paris Agreement.

The WMO’s assessment is calculated using the average global temperature across six datasets, with the period of 1850 to 1900 used to provide a pre-industrial baseline. Temperature datasets collected by various agencies and institutions around the world vary slightly, mainly due to differences in how ocean temperatures have been measured and analysed over the decades. Some of those datasets come in just below the 1.5°C mark, but others are well above.

The UK’s Met Office weather service puts 2024’s average temperature at 1.53°C above pre-industrial levels, with a margin of error of 0.08°C. That is 0.07°C above 2023, the previous warmest year on record. Meanwhile, the European Union’s climate change service Copernicus has 2024 temperatures at 1.6°C above pre-industrial levels, 0.12°C above 2023’s record.

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Berkeley Earth, a climate research group in California, , the second time in its dataset the rise in global average temperatures has breached 1.5°C, after 2023. Temperature puts the rise in temperature a bit lower at 1.47°C above pre-industrial levels, and the US National Oceanic and Atmospheric Administration . The WMO finds an average rise of 1.55°C across the six datasets, with a margin of error of 0.13°C.

������ýs agree that the surge in temperature was caused mostly by the continuation of human-caused climate change and an El Niño weather pattern, which tends to push up global temperatures. But the scale and persistence of the heat has shocked many experts, who expected temperatures to subside once El Niño ended in May 2024. Instead, they remained at record levels throughout the rest of the year.

The world’s oceans have been most affected, with sea surface temperatures staying at record levels for most of 2024, playing havoc with marine ecosystems. The year also brought no shortage of extreme weather on land, with fierce heatwaves, sharp declines in polar ice, deadly flooding and uncontrollable wildfires. “This was a year when the impacts of climate change are right across the planet,” says , former chief scientific adviser to the UK government and founder of the Climate Crisis Advisory Group.

Technically, the Paris Agreement target of limiting warming to below 1.5°C is calculated using a 20-year average, so a single year above the threshold doesn’t signal a formal breach of the target. But given the pace of warming in recent years, many scientists say the long-term Paris goal is now out of reach.

“The abrupt new records set in 2023 and 2024 join other evidence that recent global warming appears to be moving faster than expected,” said at Berkeley Earth in a statement. “Whether increased global warming is a temporary change or part of a new long-term trend remains to be seen. Already though the Paris Agreement target of staying below 1.5°C is unobtainable, and the long-term average will pass this milestone within the next five to 10 years.”

In a briefing on 9 January, at Copernicus told reporters that the Paris Agreement target was now probably impossible to achieve. “There’s an extremely high likelihood that we will overshoot the long-term average of 1.5°C and the Paris Agreement limit,” she said.

at the University of Southampton, UK, has helped develop a new global dataset, DCENT, which he says uses state-of-the-art technology to produce a more accurate historical baseline for warming levels. This new dataset suggests the global average temperature for 2024 was 1.66°C above pre-industrial levels, he says, although it isn’t included in the WMO’s calculations.

As a result, Chan also believes the 1.5°C goal is now probably out of reach. “We need to get prepared for a wider range of futures, and 1.5°C is not the only target we should be aiming for,” he says. But he stressed this should also be a critical moment to be more ambitious in cutting emissions. “It’s too early to give up,” he says.

The outlook for 2025 is still unclear. There are early signs that global sea surface temperatures have finally started to cool to expected levels. “That’s a good sign that the heat is dissipating from the surface of the ocean at least,” said Burgess. Meanwhile, after months of expectation, a La Niña phase has finally developed in the equatorial Pacific Ocean, which should dampen global temperatures into 2025.

But Chan warns that the world may have experienced a step change in warming if temperatures follow the pattern of previous El Niño events. “Every time that we see a large El Niño event… global warming is basically brought up to a new level,” he says, suggesting that 2024 could be the first of many years where average temperatures exceed 1.5°C.