As likely as not, the Earth’s average annual temperature will soon have its first spike above the 1.5 degree Celsius cap set for post-Industrial Revolution warming by the 2015 Paris Agreement, according to a new five-year climate outlook from the World Meteorological Organization. Greenhouse gas emissions have continued to increase since the pact was signed, and the WMO found there is now a 50-50 chance that the world will temporarily cross the 1.5-degree threshold sometime in the next five years.
The WMO projection is the latest in a grim drumbeat of climate science reports showing that the world is still failing to hold warming to a level that could avoid even more catastrophic climate impacts than the increasing heat waves, droughts, wildfires and tropical storms that the current level of warming, about 1.1 degrees Celsius above the pre-industrial level, has spawned.
A single year of warming above 1.5 degrees Celsius (2.7 degrees Fahrenheit) doesn’t mean that the threshold of the Paris agreement has been breached for good, said Leon Hermanson, a climate scientist with the Met Office in the United Kingdom who led the report. But the report shows the world is “edging ever closer to a situation where 1.5 degrees could be exceeded for an extended period,” he said.
Penn State climate scientist Michael Mann, who was not involved in the report, said it’s important to understand the difference between the short-term WMO projection and the planet’s long-term climate future.
“There is huge potential for misunderstanding here, particularly when it comes to avoiding dangerous planetary warming thresholds,” he said. “When we talk about the need to avoid 1.5 degrees Celsius global warming in a climate change context, we’re talking about the long-term trend, not the values for individual years.”
Annual readings will cross the threshold well before the trend line crosses it, he said.
“What we’re concerned about, when it comes to climate change impacts, is when the trend line crosses 1.5 degrees Celsius, and that likely won’t happen for decades,” he said. That circumstance could be avoided completely, he added, if carbon emissions drop fast enough, even if some short-term spikes cross the 1.5-degree threshold.
Maxx Dilley, director of the WMO’s Climate Programme, said the new research shows that the probability of the global annual mean temperature reaching or exceeding 1.5 degrees Celsius above pre-industrial levels keeps growing.
“The global annual mean temperature trend is towards increasing temperatures, with each decade currently being warmer than the previous one,” he said.
Dilley emphasized that increasing concentrations of greenhouse gases in the atmosphere are driving the temperature increase.
“As the upward trend in temperatures continues, at one point, in the not too distant future, the global annual mean temperature will reach 1.5 degrees,” he said. “After that, if greenhouse atmospheric concentrations continue rising, the global annual mean temperature will reach or exceed 1.5 degrees more often.”
The spike above 1.5 degrees Celsius could happen the next time the equatorial Pacific Ocean shifts from the current cooler La Niña phase back to El Niño, when a huge pool of warmer-than-average sea surface water can raise the average global temperature to record levels, as it did in 2016, which is tied with 2020 as the warmest year on record.
“La Niña and El Niño have a tendency to reduce or amplify, respectively, the overall average annual global mean temperature,” Dilley said. During La Niña, a large pool of cool water “tends to slightly reduce the global annual average temperature by one or two tenths of a degree Celsius. The large pool of warmer than normal sea temperatures during El Niño tends to increase it.”
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Climatologist Gavin Schmidt, director of the NASA Goddard Institute for Space Studies, said the WMO report is based on an average drawn from three sets of global temperature measurements, which might skew the projections to be a bit warmer than if they were based on any one of the individual indices.
The first time the annual average exceeds 1.5 degrees Celsius, “will be far more of a media event than a climate event,” he said. “The Paris Agreement targets are all about the long-term stabilized temperatures, not a single year.”
Still, the long-term global temperature trend is still headed in a dangerous direction. The WMO report found there is a 93 percent chance that at least one year between 2022-2026 will be the warmest on record, and a 93 percent chance that the five-year average for 2022-2026 will be higher than the last five years.
“Regardless of what is predicted here, we are very likely to exceed 1.5 degrees Celsius in the next decade or so,” Schmidt said, “but it doesn’t necessarily mean that we are committed to this in the long term, or that working to reduce further change is not worthwhile.”
The WMO report projects an increased chance of continued drought in the Southwest of United States and southwestern Europe, both regions that are already seeing increased tree die-offs, agricultural losses and wildfires due to warmer and drier conditions. It noted an increased probability of wetter conditions in northern Europe, the Sahel, parts of Brazil and Australia.
The 1.5-degree Celsius figure is not just a random statistic, said WMO Secretary-General Petteri Taalas, but an indicator of the point at which climate impacts will become increasingly harmful for people and the planet.
“For as long as we continue to emit greenhouse gases, temperatures will continue to rise,” he said. “And alongside that, our oceans will continue to become warmer and more acidic, sea ice and glaciers will continue to melt, sea level will continue to rise and our weather will become more extreme.”