The sun sets on a hot day in London in July 2024Guy Corbishley/AlamyHopes of keeping global warming below 1.5C 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) will declare later today, in the latest stark warning that humanity is pushing Earths climate into uncharted territory. AdvertisementThe average global temperature for the year exceeded 1.5C above the pre-industrial baseline for the first time, the agency will also confirm, breaching the threshold set by the Paris Agreement.The WMOs 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 will come in just below the 1.5C mark, New Scientist understands, but others are well above.The UKs Met Office weather service puts 2024s average temperature at 1.53C above pre-industrial levels, with a margin of error of 0.08C. That is 0.07C above 2023, the previous warmest year on record. Meanwhile, the European Unions climate change service Copernicus has 2024 temperatures at 1.6C above pre-industrial levels, 0.12C above 2023s record. Unmissable news about our planet delivered straight to your inbox every month.Sign up to newsletterScientists agree that the surge in temperature was caused mostly by the continuation of human-caused climate change and an El Nio 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 Nio ended in May 2024. Instead, they remained at record levels throughout the rest of the year.The worlds 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 David King, 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 1.5C is calculated using a 20-year average, so a single year above the threshold doesnt 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.In a briefing on 9 January, Samantha Burgess at Copernicus told reporters that the Paris Agreement target was now probably impossible to achieve. Theres an extremely high likelihood that we will overshoot the long-term average of 1.5C and the Paris Agreement limit, she said.Duo Chan 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 1.66C above pre-industrial levels, he says, although it isnt included in the WMOs calculations.As a result, Chan also believes the 1.5C goal is now probably out of reach. We need to get prepared for a wider range of futures, and 1.5C 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. Its 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. Thats 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 Nia 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 Nio events. Every time that we see a large El Nio 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 1.5C.Topics:climate change