Four major meteorological agencies have now confirmed that 2018 was the fourth-warmest year on record, with the UK Met Office calculating a 10% chance that average global warming will temporarily exceed the critical 1.5°C threshold in at least one of the next five years.
2018 takes its places in the list of warmest years ever recorded behind 2016, 2015, and 2017, The Associated Press reports, with average temperature of 14.69°C/58.42°F. Scientists at NASA and the U.S. National Oceanographic and Atmospheric Administration (NOAA) attributed the marginal drop from the three previous years to random weather variations.
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“Never mind the little wiggles from year to year. The trend is going relentlessly up, and it will continue to do so,” said Potsdam Institute climate scientist Stefan Rahmstorf. “Those who live in denial of this fact are in denial of physics.”
That trend could bring average warming more than 1.5°C above pre-industrial levels sometime between now and 2023, though the effect would be temporary for now, the Met Office concluded.
“A run of temperatures of 1.0°C or above would increase the risk of a temporary excursion above the threshold of 1.5°C above pre-industrial levels,” said  research fellow Dr. Doug Smith. “Predictions now suggest around a 10% chance of at least one year between 2019 and 2023 temporarily exceeding 1.5°C.”
The Met Office’s predictions would make 2014-2023 the warmest decade in more than 150 years of temperature records, the BBC notes .
“Although it would be an outlier, scientists said the first appearance in their long-term forecasts of such a ‘temporary excursion’ was worrying, particularly for regions that are usually hard hit by extreme weather related to El Niño,” including western Australia, South America, south and west Africa, and India’s monsoon belt, The Guardian reports. But climate scientists “stressed this did not mean the world had broken the Paris Agreement 80 years ahead of schedule because international temperature targets are based on 30-year averages.”
“Exceeding 1.5°C in one given year does not mean the 1.5°C goal has been breached and can be redirected towards the bin,” said Grantham Institute lecturer Joeri Rogelj, a coordinating lead author on last year’s landmark IPCC report  on 1.5°C pathways. “The noise in the annual temperatures should not distract from the long-term trend.”
Rogelj added that “breaching 1.5°C of global warming does indeed mean that we failed to limit warming to that ‘safe’ level, but not that our understanding of a safe level of climate change has suddenly changed and climate change should go unchecked.”