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The decade ending in 2020 was the hottest in recorded history, with temperatures higher than any other period in at least two millennia and possibly much longer. The main culprit behind the extreme warming, atmospheric carbon dioxide, has reached a level not seen in at least 3 million years. The last seven years are now the warmest since measurement began in the 19th century.
In five major temperature datasets updated on Thursday, 2020 finished in a statistical tie with 2016 as the hottest year on record, coming in about 1.2° Celsius hotter than the 19th century. Four of the five research centers showed 2020 slightly cooler than 2016, but within the uncertainty window. The year 2019 is a very close third.
“That’s the global average,” said Ahira Sánchez-Lugo, a physical scientist at the U.S. National Oceanic and Atmospheric Administration’s National Centers for Environmental Information, one of the scientific groups reporting new annual temperature data. “There are some regions that are warming a lot faster.” One degree may sound small, she added, but “a small change in the global temperature average can lead to big changes when it comes to extreme weather. We're already seeing that.”
Heatwaves, wildfires, more intense storms, and changes in rain and snow all point to a world already facing heightened danger. With each passing year, scientists grow more confident in attributing many of these weather anomalies to the heat trapped in the atmosphere and oceans. “When the ingredients for a hurricane come together, we’re seeing that these hurricanes are intensifying a lot faster,” Sánchez-Lugo said. “They’re moving slower, and the precipitation rates associated with these hurricanes are increasing as well.”
The record-high temperatures of 2016 had temporary help from El Niño, the naturally occurring Pacific Ocean phenomenon that raises thermometers. That wasn’t the case for 2020, which not only lacked the irregular warming trend but also featured an appearance from El Niño’s cooling counterpart, La Niña, beginning in August. January through November each ranked among the top four warmest occurrences of that month; December came in as the eighth warmest, helping lower the annual average.
Ocean temperatures also hit a new high in 2020, according to a separate study published this week.
Temperature data has borne out many of the projections made by climate researchers. The modeling work continues in the climate science community, with the next reports from the United Nations-backed Intergovernmental Panel on Climate Change expected this year and next.
“The models did as well as could be expected in correctly predicting what was to come and what has now occurred,” said Gavin Schmidt, director of NASA’s Goddard Institute for Space Studies, which released the space agency’s temperature data on Thursday. In NASA’s results 2020 just edges out 2016 to set a new record, within the margin of error.
NOAA’s NCEI, Berkeley Earth, the University of East Anglia’s Climate Research Unit, and the “Cowtan and Way” record started by two scientists, all found 2020 to come in very close behind 2016. A sixth research group, the European Union’s Copernicus Climate Change Service called 2020 and 2016 a tie. There’s no disagreement that the 10 hottest years on record have all occurred since 2005.
The scale of humanity’s CO₂ pollution is so great that the pandemic-caused economic crash will barely register in emissions data, let alone the average temperature. The International Energy Agency estimates that CO₂ emissions fell about 8 per cent last year compared to 2019, or equivalent to the pollution level in 2010, and BloombergNEF has suggested that 2019 may turn out to represent peak CO₂ emissions from fossil-fuel burning. The U.S. alone saw a drop in all greenhouse gases of 10.3 per cent, according to Rhodium Group, a research firm. The U.K.’s Met Office projects atmospheric CO₂ in 2021 will rise more than 50 per cent above the preindustrial level for the first time.
Publicizing the inexorable rise in global average temperature has become a grim routine for scientists. Andrew Dessler, a professor of atmospheric sciences at Texas A&M University, wrote on Twitter of the utter predictability of his comments following each year’s new temperature data.
Dessler said he finds himself vacillating between two thoughts. “On one hand, this is dog-bites-man stuff—completely unsurprising,” he said in an interview. Yet it’s also “somewhat shocking to me how fast the warming seems to be proceeding.”
NOAA already gives 2021 a 99.6 per cent chance of being a top 10 hottest year. Just don’t expect another record breaker. With La Niña, this year has only a 7.4 per cent chance of surpassing the temperatures of 2020 and 2016.