by Deadly heat in the South West. Hot tub temperatures in the Atlantic Ocean. Sweltering conditions in Europe, Asia and South America.
2023 was the hottest year on record on earth, in some ways it’s no surprise. For decades, scientists have been sounding the alarm about rapidly rising temperatures due to humanity’s relentless burning of fossil fuels.
But last year’s sudden spike in global temperatures blew far beyond what statistical climate models had predicted, prompting one climate scientist to warn that the world could be entering an “Uncharted End .”
“It is alarming and disturbing to admit that no year has affected the forecasting abilities of climate scientists more than 2023,” wrote Gavin Schmidt, director of NASA’s Goddard Institute for Space Studies, in a recent article in journal. nature.
Now, he and other researchers are scrambling to explain why 2023 was such a hot anomaly. Many theories have been proposed, but “so far, no combination of them has been able to reconcile our theories with what happened,” Schmidt wrote.
Last year’s global average temperature of 58.96 degrees was about a third of a degree warmer than the previous warmest year in 2016, and about 2.67 degrees warmer than the pre-industrial period of the late 1800s against which global warming is measured .
While human-induced climate change and El Niño can account for much of that warming, Schmidt and other experts say the extra three to four tenths of a degree is harder to account for.
Theories for the increase include a 2020 change to aerosol shipping regulations designed to help improve air quality around ports and coastal areas, which could have the unintended consequence of allowing more sunlight reach the planet.
The Hunga Tonga-Hunga Ha’apai volcano in 2022 shot millions of tons of water vapor into the stratosphere, which scientists say helped trap some heat. In addition, a recent uptick in the 11-year solar cycle may have added about a tenth of an additional warning.
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But these factors alone cannot explain what is happening, Schmidt said.
“Even after all plausible explanations are taken into account, the difference between expected annual average temperatures and observed temperatures in 2023 remains around 0.2 °C – about the gap between the previous annual record and the annual record current,” he wrote in his report.
On the phone, Schmidt said he thinks one of three things could be going on.
The year 2023 could be a “blip” – a perfect storm of Earth’s natural variables and cycles converging to create one very hot year. If that were to happen, “it won’t have big implications for what we see in the future, because it would just be a rare and unlikely thing that won’t happen again soon,” he said.
However, he indicated that it is unlikely, because those elements “never in a line up to give us a blip this big.”
Another possibility is that scientists have a misunderstanding of the driving forces of climate change. Although greenhouse gases, volcanic eruptions and aerosols are known to affect global temperature, the full magnitude of their effects may have been underestimated or miscalibrated. If so, he said, hopefully research and data sets will come up soon.
The last explanation he offered is that the system itself is changing – and changing in ways that are faster and less predictable than previously understood.
“That would be worrying because science is about taking information from the past, looking at what’s going on, and making predictions about the future,” Schmidt said. “If we can’t trust the past, we have no idea what will happen.”
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Not everyone agrees with his assessment, however. Michael Mann, President’s Distinguished Professor in the Department of Earth and Environmental Science at the University of Pennsylvania, said the premise that the 2023 warming cannot be explained — or is inconsistent with model simulations — is “simply wrong.”
“The situation is very similar to what we saw during the 2014-2016 period as we transitioned from several years of La Niña conditions to a major El Niño event, and then back to La Niña,” Mann said in an email. .
Indeed, he said some recent modeling shows that the global temperature spike in 2016 was even more extreme than in 2023.
“The plot shows that the warming of the planet’s surface is proceeding almost exactly as predicted,” Mann said. “And the models show that warming will continue rapidly as long as we continue to burn fossil fuels and generate carbon pollution.”
When asked about this interpretation, Schmidt said it was true that the period 2014 to 2016 was similarly anomalous. But there is a key difference between then and now, he said.
The 2016 temperature spike came on the heels of an El Niño event, with the biggest anomalies in February, March and April of the year after its peak, he said. He noted that similar patterns occurred after previous El Niños in 1998 and 1942.
By contrast, last year’s spike occurred in August, September, October and November — before the peak of El Niño — “and that’s never happened before,” Schmidt said. “It’s never happened in our temperature record. It doesn’t happen in the climate models.”
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Alex Hall, a professor of atmospheric and oceanic sciences at UCLA, said he largely agrees with Schmidt’s assessment that hypothetical factors alone cannot account for the large temperature anomaly in 2023 and early 2024. .He compared it to the emergence of megafires, or extreme wildfires, in the last decade, which was completely unexpected.
“What we have learned is that there is an aspect of this that is not fully predictable – that we do not fully understand – and that we are tempting fate here a little by continuing to disrupt the climate system,” said Hall. . “It’s going to do things that we don’t understand, that we don’t expect, and that’s going to have big impacts.”
Hall said the rapid transition from a persistent La Niña to a strong El Niño last summer likely played a role, as did the change in aerosol regulations.
He added that the rapid loss of Antarctic sea ice in 2023 – itself a result of a warmer planet and oceans – could create a kind of feedback loop that contributed to further warming. Ice and snow are reflective, so when they melt, it can result in a darker ocean that absorbs more heat and sunlight. (Antarctic sea ice coverage fell to a record low in 2023, according to the National Oceanic and Atmospheric Administration.)
“It’s a planetary emergency for us to figure out what’s going on when we see these kinds of changes,” Hall said. “There should be big teams of people working on it to try to understand it, and we don’t really have those kinds of efforts, so I think there are also lessons in the need to focus on the particular subject this.”
While he and other scientists may not agree on how extraordinary 2023 was — or what was behind its exceptional heat — they all acknowledged the clear signs that a planet was being pushed to its limits.
“I think it is unfortunate that so much has been made of the El Niño-spiked global temperatures of 2023, where in my opinion there is nothing surprising, or inconsistent with model predictions,” said Mann. “There are much better scientific reasons to be concerned about the looming climate crisis – especially the killing of horrific weather extremes, heat waves, wildfires, floods, droughts, which are exceeding model predictions in several measures.”
Last year was marked by extreme weather events, with more billion-dollar disasters in the United States than any other year, according to NOAA. These included the Lahaina wildfire in Hawaii in August; Hurricane Idalia in Florida that same month; and severe flooding in New York in September.
Already this year, January and February have continued the global hot streak, marking nine consecutive months of record high temperatures.
In his Nature article, Schmidt said the unexplained aspects of recent warming have revealed an “unprecedented knowledge gap” in today’s climate monitoring, prompting the need for more nimble data collection that can keep up with the pace of change.
He noted that it could take months or even years for researchers to unpack all the factors that may have played a part in the sizzling conditions.
“We need answers as to why 2023 turned out to be the warmest year in possibly the last 100,000 years,” he wrote. “And we need them quickly.”
Although El Niño is expected to wane this summer, there is a 45% chance that this year will be warmer than 2023, according to NOAA.
However, it is almost certain that 2024 will be one of the five hottest years on record — so far.
This story originally appeared in the Los Angeles Times.
