The World Meteorological Organization and the UK Met Office project an 86% chance that the Earth's temperature will exceed the 1.5°C threshold set by the Paris Agreement in at least one of the next five years, and a 70% probability that the five-year average from 2025 to 2029 will surpass that mark.
"Higher global mean temperatures may sound abstract, but it translates in real life to a higher chance of extreme weather: stronger hurricanes, stronger precipitation, droughts," said Natalie Mahowald, a climate scientist at Cornell University who was not involved in the forecast. "So higher global mean temperatures translates to more lives lost."
For the first time, scientists now say there is a statistical possibility - albeit small, at around 1% - that a year before 2030 could see global temperatures reach 2°C above pre-industrial levels, a development described by experts as alarming. "It is shocking that 2C is plausible," said Adam Scaife of the UK Met Office. "It has come out as only 1% in the next five years but the probability will increase as the climate warms."
The five-year forecast, issued Wednesday, is based on over 200 simulations by research institutions including the Canadian Centre for Climate Modelling and Analysis and the Barcelona Supercomputing Centre. The models take into account short-term weather fluctuations as well as long-term climate projections.
Leon Hermanson of the UK Met Office, who led the production of the report, stated: "It's not something anyone wants to see, but that's what the science is telling us." He added that 2025 is likely to be one of the three warmest years on record.
Regions across the globe are not expected to be affected equally. The Arctic is forecast to continue warming at 3.5 times the global average due to rapid sea ice loss, which affects sunlight reflection. More rainfall is expected in South Asia, the Sahel, and northern Europe, while the Amazon is projected to face intensified droughts.
"With the next five years forecast to be more than 1.5C warmer than preindustrial levels on average, this will put more people than ever at risk of severe heat waves, bringing more deaths and severe health impacts unless people can be better protected from the effects of heat," said Richard Betts, head of climate impacts research at the UK Met Office.
Johan Rockstrom, director of the Potsdam Institute for Climate Impact Research, wrote: "We will experience higher frequency and more extreme events (particularly heat waves but also droughts, floods, fires and human-reinforced hurricanes/typhoons)."
Climate variability driven by El Niño patterns and other natural phenomena have historically caused temporary spikes, but researchers noted a new trend where elevated temperatures persist. "Record temperatures immediately become the new normal," said Rob Jackson, a climate scientist at Stanford University.
Chris Hewitt, director of climate services at the WMO, stressed that urgent mitigation efforts could still make a difference. "We must take climate action," he said. "1.5C is not inevitable."
