For the first time ever, global temperatures are now more likely than not to breach 1.5 degrees Celsius (2.7 degrees Fahrenheit) of warming within the next five years, the World Meteorological Organization (WMO) said on Wednesday.
This does not mean the world would cross the long-term warming threshold of 1.5C above preindustrial levels set out in the 2015 Paris Agreement.
But a year of warming at 1.5C could offer a glimpse of what crossing that longer term threshold, based on the 30-year global average, would be like.
With a 66% chance of temporarily reaching 1.5C by 2027, "it's the first time in history that it's more likely than not that we will exceed 1.5C," said Adam Scaife, head of long-range prediction at Britain's Met Office Hadley Centre, who worked on the WMO's latest Global Annual to Decadal Climate Update.
Last year's report put the odds at about 50-50.
Even temporarily reaching 1.5C is "an indication that as we start having these years with 1.5C happening more and more often, than we are getting closer to having the actual long-term climate be on that threshold," said Leon Hermanson, also of the Met Office Hadley Centre.
It also means the world has failed to make sufficient progress on slashing climate-warming greenhouse gas emissions.
Partially responsible for boosting the chance of soon hitting 1.5C is an El Niño weather pattern expected to develop in the coming months. During El Niño, warmer waters in the tropical Pacific heat the atmosphere above, lifting global temperatures.
The El Niño "will combine with human-induced climate change to push global temperatures into uncharted territory", said WMO Secretary-General Petteri Taalas in a press statement.
A mid-year switch to El Niño is worrying scientists across the world. The weather phenomenon, while distinct from climate change, is likely to boost extremes and bring warmer weather to North America and drought to South America, with the Amazon at greater risk of bad fires.
The likelihood of temporarily exceeding 1.5C has increased over time. Scientists had estimated just a 10% chance of hitting 1.5C between 2017 and 2021, for example.
Unlike the U.N. Intergovernmental Panel on Climate Change's climate projections, which are based on future greenhouse gas emissions, the WMO update provides more of a prediction-based long-range weather forecast.
The WMO also found a 98% chance that one of the next five years will be the hottest on record, surpassing 2016 which saw a global temperature impacted by about 1.3C (2.3F) of warming.
"This report must be a rallying cry to intensify global efforts to tackle the climate crisis," said Doug Parr, chief scientist at Greenpeace UK.
