Earth is ending its hottest year in 174 years, and likely in 125,000.
An unrelenting heat wave has roasted Phoenix and Argentina. Wildfires are raging across Canada. Thousands have died in floods in Libya. Winter ice cover in the dark seas around Antarctica is at an unprecedented low.
Global temperatures this year have not only beaten previous records. They left them in the dust. From June to November, mercury spent months climbing the charts. December temperatures remained largely above normal: Much of the Northeastern United States is expecting spring-like conditions this week.
That’s why scientists are already examining the evidence — from oceans, volcanic eruptions, even pollution from cargo ships — to see if this year might reveal something new about the climate and what we’re doing with it.
One hypothesis, perhaps the most troubling, is that global warming is accelerating, with the effects of climate change hitting our way faster than ever. “What we’re looking for, really, is a body of corroborating evidence that all points in the same direction,” said Chris Smith, a climate scientist at the University of Leeds. “Then we look for causality. And that’s going to be really interesting.”
As extreme as the temperatures were this year, they didn’t catch the researchers off guard. Scientists’ computational models offer a range of projected temperatures, and the heat of 2023 is still well within this range, albeit at the high end.
By itself, an exceptional year isn’t enough to suggest there’s something wrong with the computer models, said Andrew Dessler, an atmospheric scientist at Texas A&M University. Global temperatures have long fluctuated around steady warming due to cyclical factors such as El Niño, the climate pattern that emerged in the spring and has intensified since, potentially signaling more record-breaking heat coming in 2024.
“Your default position should be, ‘The models are right,'” says Dr. Dessler. “I’m not ready to say ‘we messed up the climate’ or there’s anything weird going on until more evidence comes in.”
One thing the researchers will be looking at is whether something unexpected might happen in the interplay of two major climate influences: the warming effect of greenhouse gases like carbon dioxide and the cooling effect of other type of industrial pollution.
For most of the past 174 years, humans have been filling the skies with both greenhouse gases and aerosols, or tiny particles from smokestacks, tailpipes and other sources. These particles are harmful to the lungs when inhaled. But in the atmosphere, they reflect solar radiation, slightly reducing the heat-warming effect of carbon dioxide.
In recent decades, however, governments have begun to reduce aerosol pollution for public health. This has led to rapid temperature increases since 2000, scientists estimate.
And in a much-discussed report last month, climate researcher James E. Hansen argued that scientists are grossly underestimating how much the planet will warm in the coming decades if countries cleans aerosols without cutting carbon emissions.
Not all scientists are convinced.
Arguments like Dr. Hansen is difficult to discuss patterns in recent decades, said Reto Knutti, a climate physicist at the Swiss university ETH Zurich. In recent years, scientists have also discovered that global warming is shaped not only by how much heat is trapped near the Earth’s surface but also by how and where this heat is distributed across the planet. .
This makes it more difficult to conclude with confidence that warming is ready to accelerate, Dr. Knutti. Until the current El Niño ends, “we probably won’t be able to make definitive claims,” he said.
Pinning down the precise scale of the aerosol effect has also been difficult.
Part of how aerosols cool the planet is by making clouds brighter and deflecting more solar radiation. But the clouds are very complex, coming and going and leaving several clues for scientists to analyze, said Tianle Yuan, a geophysicist at NASA and the University of Maryland, Baltimore County. “That’s the main reason it’s a hard problem,” he said.
This year, aerosols are of particular interest because of a 2020 international regulation restricting pollution from ships. Dr. is trying Yuan and others determined how much regulation may have increased global temperatures in recent years by limiting aerosols that reflect sunlight.
The argument of Dr. Hansen for the faster warming depends on the climatic reorganizations between the ice ages of the last 160,000 years.
Using Earth’s distant past to make inferences about climate in the coming years and decades can be tricky. However, the deep history of the planet shows how unique the current period is, said Bärbel Hönisch, a scientist at Columbia’s Lamont-Doherty Earth Observatory.
Fifty-six million years ago, for example, geologic turmoil added carbon dioxide to the atmosphere in quantities comparable to what humans are adding today. Temperatures jump. The oceans have become acidic. The species died out en masse.
“The difference was that it took about 3,000 to 5,000 years to get there” then, Dr. Hönisch, compared to several centuries ago.
Then it took Earth longer to neutralize that excess carbon dioxide: about 150,000 years.
Nadja Popovich contributed reporting.
