by David Gelles - New York Times
From his office at the University of Miami, Brian McNoldy, an expert in hurricane formation, is tracking the latest temperature data from the North Atlantic with a mixture of concern and bewilderment.
For the past year, oceans around the world have been substantially warmer than usual. Last month was the hottest January on record in the world’s oceans, and temperatures have continued to rise since then. The heat wave has been especially pronounced in the North Atlantic.
“The North Atlantic has been record-breakingly warm for almost a year now,” McNoldy said. “It’s just astonishing. Like, it doesn’t seem real.”
Across the unusually warm Atlantic, in Cambridge, England, Rob Larter, a marine scientist who tracks polar ice levels, is equally perplexed.
“It’s quite scary, partly because I’m not hearing any scientists that have a convincing explanation of why it is we’ve got such a departure,” he said. “We’re used to having a fairly good handle on things. But the impression at the moment is that things have gone further and faster than we expected. That’s an uncomfortable place as a scientist to be.”
Spin the globe to the south, and the situation is similarly dire.
“The sea ice around the Antarctic just not growing,” said Matthew England, a professor at the University of New South Wales who studies ocean currents. “The temperature’s just going off the charts. It’s like an omen of the future.”
What’s driving the heat?
Global warming, caused by the burning of fossil fuels, has been driving up global temperatures on land and in the sea for decades now. Over the past year, worldwide average temperatures were more than 1.5 degrees Celsius, or 2.7 degrees Fahrenheit, higher than before the industrial age. New data from a variety of sources has led some climate scientists to suggest that global warming is accelerating.
Given the overall warming trend, higher temperatures in the oceans aren’t a complete surprise. Oceans absorb most of the additional heat that greenhouse gasses trap near the surface of the Earth, and have been steadily warming for years. The current El Niño weather cycle is also leading to additional heat in the Pacific Ocean and allowing more energy to be released into the atmosphere.
Yet the past year has come as a shock even to those who follow the data closely.
“We all know that there’s been a rapid warming, particularly over the last few decades,” Larter said. “But it over the last 18 months, it’s jumped up beyond what we expected.”
Scientists are offering a range of explanations for the record heat in the North Atlantic.
One surprising factor may be a reduction in pollution in the area. In 2020, a new rule went into effect that limited the amount of sulfur dioxide contained in the fuel used by container ships. That has reduced the amount of particulate matter in the air, which let in more solar radiation and contributed to global warming.
“When those aerosols were in the sky above the shipping lanes, they helped create a cloud cover, and there’s much less now,” McNoldy said. “That’s a legitimate thing.”
But the reduction of sulfur dioxide alone can’t explain the North Atlantic’s extreme heat, scientists said.
Another factor may be the complex feedback loops in the Earth’s weather patterns. The North Atlantic has been unusually clear lately, with fewer clouds than normal to block the sunlight from heating the water. The area has also been less windy than normal, which may have also led to a spike in temperatures.
Without strong winds, colder water from deeper in the ocean doesn’t rise to the surface as readily, England said.
What comes next
In the near term, McNoldy said the warmer waters in The Atlantic could fuel a strong and lengthy hurricane season.
“Compared to other fairly significant hurricane seasons, this is way warmer at this point in the year,” he said.
The marine heat is also expected to reduce Arctic sea ice, Larter said.
“What’s bad news for sea ice has a lot of knock-on effects,” he said. “The formation of sea ice is the process that really drives a lot of the ocean’s circulation. And if the overturning circulation slows down, that really has climate impacts across the world.”
Recent research has suggested that as glaciers melt and more fresh water enters the Atlantic, a crucial ocean current could falter, potentially leading to drastic changes in global weather patterns, such as a rapid reduction in temperatures across Europe.
McNoldy said it was too early to say whether the ongoing heat wave is part of the early stages of such a change. “I hope it’s not something much worse, like, you know, like some significant change in the ocean current,” he said. “That would have far greater implications.”