The world is “inexorably closer” to breaching a key temperature limit in the next five years, according to a UN report.
The major study said there was now a 40 per cent chance global temperature will cross the 1.5C threshold set by the Paris Climate Accord during at least one of the next five years - but the odds are rising.
That level of temperature increase would most likely be temporary, but scientists warn it is the ceiling to avoid the most catastrophic effects of climate change.
Hitting the threshold once does not mean the Paris Accord has failed, as the agreement measures temperature rises over a 30-year average, rather than a single year.
However, UN World Meteorological Organisation secretary-general Petteri Taalas said the finding underscores "we are getting measurably and inexorably closer" to runaway climate change.
“We are getting measurably and inexorably closer to the lower target of the Paris Agreement on climate change,” he said.
“It is yet another wakeup call that the world needs to fast-track commitments to slash greenhouse gas emissions and achieve carbon neutrality.”
Every year from 2021 through 2025 is likely to be at least 1C warmer, according to the study.
The report also foresees a 90 per cent chance that at least one of those years will become the warmest year on record, topping 2016 temperatures.
In 2020 - one of the three warmest years on record - the global average temperature was 1.2C above the pre-industrial baseline, according to an April WMO report.
Gavin Schmidt, director of Nasa's Goddard Institute for Space Studies, said the long-term trends were “unrelenting”.
"It seems inevitable that we're going to cross these boundaries," he said.
“That's because there are delays in the system, there is inertia in the system, and we haven't really made a big cut to global emissions as yet."
Almost all regions are likely to be warmer in the next five years than in the recent past, the UN report said.
The WMO uses temperature data from multiple sources including NASA and the National Oceanic and Atmospheric Administration.
Weather that was once unusual is now becoming typical. Earlier this month, for example, NOAA released its updated "climate normals" which provide baseline data on temperature and other climate measures across the US.
The new normals - updated every 10 years - showed that baseline temperatures across the US are overwhelmingly higher compared with the past decade.
Russell Vose, chief of the climatic analysis and synthesis branch at NOAA's National Centres for Environmental Information, said shifts were occurring both on average and in temperature extremes.
He said the temperature extremes were "more likely what people will notice and remember”.
Warming temperatures also affect regional and global precipitation. As temperatures rise, evaporation rates increase and warmer air can hold more moisture. Climate change also can shift circulation patterns in the atmosphere and ocean.
The UN report predicts an increased chance of tropical cyclones in the Atlantic Ocean, that Africa's Sahel and Australia will likely be wetter, and that the south-west of North America is likely to be drier.
The projections are part of a recent WMO effort to provide shorter-range forecasts of temperature, rainfall and wind patterns, to help nations keep tabs on how climate change may be disrupting weather patterns.
