Now, an unprecedented streak of ocean warming is entering its second year. Scientists say this may represent a major change in Earth's systems that cannot be reversed on any human time scale.
That's because what they've seen in the oceans so far “doesn't make sense,” Gavin Schmidt, director of NASA's Goddard Institute for Space Studies, told The Washington Post.
“This could mean that global warming is already fundamentally changing how the climate system works, much sooner than scientists expected,” he wrote in an article. column In the journal Nature.
Ocean temperatures jump 'off the charts'
The warming has extended well beyond the Pacific region affected by El Niño.
For example, across most of the Atlantic Basin, surface temperatures were 1 to 2 degrees Celsius (1.8 to 3.6 degrees Fahrenheit) above the 1971-2000 baseline. The anomaly is 3 degrees Celsius (5.4 degrees Fahrenheit) or more in some waters off South Africa, Japan and the Netherlands, according to National Oceanic and Atmospheric Administration satellite data.
The ocean heat waves coincide with the warmest conditions ever observed in the atmosphere. Last year, average global air temperatures rose higher than humans have ever known, and the planet may have reached its hottest temperatures in more than 100,000 years. Climate scientists expect 2024 to be warmer.
Celeste Saulo, Secretary-General of the World Meteorological Organization, said seeing such dramatic warming across the Earth's oceans is even more worrying, given that heating water requires much more energy than air.
“The time scale of the oceans is not as fast as the atmosphere,” Saulo said at a news conference. “Once a change occurs, I would say it is almost irreversible on time scales ranging from centennial to millennium.”
In its annual State of the Climate report released on Tuesday, the organization said that several climate indicators last year “have given ominous new significance to the phrase ‘off the charts’.” This included unprecedented melting of glaciers, loss of Antarctic sea ice, and rising sea levels as seas deteriorate. Heat waves will spread across more than 90% of ocean surfaces at some point during 2023.
The World Meteorological Organization said that the most exceptional warmth hit the eastern North Atlantic, the Gulf of Mexico, the Caribbean, the North Pacific, and large areas of the Southern Ocean. Since April, global average sea surface temperatures have reached record levels every month, with record highs set in July, August and September “by a particularly wide margin,” the organization said.
The effects are profound, but unpredictable
The warming of the world's oceans is already having devastating consequences for coral reefs. Deadly heat levels hit a largely unspoilt section of Australia's Great Barrier Reef this month, a repeat of the bleaching and death of coral reefs around Florida last year.
Other effects will take longer to detect.
There are fears that rising temperatures and melting could lead to the collapse of a major Atlantic current system, although the tipping point at which this might occur is unknown. It will have huge impacts on underwater ecosystems and weather patterns.
There are likely to be cascading impacts on marine life.
And in the Gulf of Maine, where waters are warming much faster than the world's oceans as a whole, researchers have already seen important species like cod and herring struggling to find cooler waters within their natural geographic range. Many fish grow more quickly at an early age, but then stabilize at smaller sizes, a sign that they are not getting enough food or that heat is stressing their bodies, said Katherine Mills, a senior scientist at the Gulf of Maine Research Institute. .
Mills said the temperatures observed over the past year were so extreme compared to past conditions, it was becoming difficult to reliably predict what the consequences might be. She said current data on ecosystem changes is becoming too outdated, too quickly.
“We generally expect that there will be temperature variation in the ocean,” Mills said. “What this did was send that variation well into a range we've never encountered before.”
“I think it's a real wake-up call,” she added.
Scientists do not know whether the extreme warming of the oceans will subside or not. So far, none of their theories about what drives them has been able to answer all the questions.
Some of the warming is likely related to decreased air pollution from cargo ships, allowing more sunlight to reach ocean surfaces. An eruption of the Hunga Tonga-Hapai underwater volcano near the island of Tonga in 2022 sent massive amounts of water vapor – a greenhouse gas that warms the planet – into the atmosphere. But neither factor explains the dramatic rise in ocean temperatures.
Ocean temperatures rose last spring at the end of what had been three consecutive years of a La Niña global climate pattern, which is the opposite of El Niño and is known to suppress global warming. The shift from La Niña to what has become the historically strong El Niño, known for warming planets, could explain much of the jump in ocean warmth, said Boyen Huang, a oceanographer at the National Oceanic and Atmospheric Administration who focuses on analyzing ocean temperatures.
Therefore, ocean temperatures could decline later this year with La Niña conditions expected to return.
But it remains to be seen whether the shift from El Niño to La Niña will be enough to significantly counter global warming or the power of greenhouse gases. This could become more evident by late summer, Huang said, if ocean temperatures continue to set records.
If record warmth persists even under La Niña conditions, Schmidt wrote, “the world will be in uncharted territory,” with far greater uncertainty about its future climate than scientists previously knew.
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