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The world’s oceans have suddenly spiked much hotter and well above record levels in the last few weeks, with scientists trying to figure out what it means and whether it forecasts a surge in atmospheric warming.
Some researchers think the jump in sea surface temperatures stems from a brewing and possibly strong natural El Niño warming weather condition plus a rebound from three years of a cooling La Niña, all on top of steady global warming that is heating deeper water below, The Associated Press reports. If that’s the case, they said, record-breaking ocean temperatures this month could be the first in many heat records to shatter.
From early March to last week, the global average ocean sea surface temperature jumped nearly 0.2°C (0.36°F), according to the University of Maine’s Climate Reanalyzer, which climate scientists use and trust. That may sound small, but for the average of the world’s oceans—which account for 71% of Earth’s area—to rise so much in that short a time, “that’s huge,” said University of Colorado climate scientist Kris Karnauskas. “That’s an incredible departure from what was already a warm state to begin with.”
Greenland Ice Loss in ‘Hyperdrive’
Just a week earlier, AP reported that the Greenland and Antarctic ice sheets are now losing more than three times as much ice a year as they were 30 years ago, according to a new comprehensive international study.
Using 50 different satellite estimates, researchers found that Greenland’s melt has gone into hyperdrive in the last few years. Greenland’s average annual melt from 2017 to 2020 was 20% more a year than at the beginning of the decade and more than seven times higher than its annual shrinkage in the early 1990s.
The new figures “are pretty disastrous really,” said study co-author Ruth Mottram, a climate scientist at the Danish Meteorological Institute. “We’re losing more and more ice from Greenland.”
Study lead author Ines Otosaka, a glaciologist at the University of Leeds in the United Kingdom, said speeded-up ice sheet loss is clearly caused by human-caused climate change.
From 1992 to 1996, the two ice sheets—which hold 99% of the world’s freshwater ice—were shrinking by 105 billion tonnes per year, two-thirds of it from Antarctica.
But from 2017 to 2020, the newest data available, the combined annual melt soared to 372 billion tonnes, more than two-thirds of it from Greenland, said the study in the journal Earth System Science Data.
That study coincided with the World Meteorological Organization’s April 21 warning that the last eight years were the eight warmest on record, with sea level rise and ocean warming hitting new highs. “The relentless advance of climate change brought more drought, flooding ,and heat waves to communities around the world last year, compounding threats to people’s lives and livelihoods,” the UN agency said.
An ‘Extreme Event on a Global Scale’
Climate scientists have been talking about the ocean warming on social media and amongst themselves, AP writes. Some, like University of Pennsylvania’s Michael Mann, quickly dismiss concerns by saying it is merely a growing El Niño on top of a steady human-caused warming increase.
The waters have warmed especially off the coast of Peru and Ecuador, where before the 1980s most El Niños began. El Niño is the natural warming of parts of the equatorial Pacific that changes weather worldwide and spikes global temperatures. Until last month, the world has been in the flip side, a cooling phenomenon called La Niña, that has been unusually strong and long, lasting three years and causing extreme weather.
Other climate scientists, including U.S. National Oceanic and Atmospheric Administration oceanographer Gregory C. Johnson, say the sudden warming doesn’t appear to be caused solely by El Niño. There are several marine heat waves or ocean warming spots that don’t fit an El Niño pattern, such as those in the northern Pacific near Alaska and off the coast of Spain, he said.
“This is an unusual pattern. This is an extreme event at a global scale” in areas that don’t fit with merely an El Niño, said Princeton University climate scientist Gabe Vecchi. “That is a huge, huge signal. I think it’s going to take some level of effort to understand it.”
The University of Colorado’s Karnauskas took global sea surface temperature anomalies over the past several weeks and subtracted the average temperature anomalies from earlier in the year to see where the sudden burst of warming is highest. He found a long stretch across the equator from South America to Africa, including both the Pacific and Indian oceans, responsible for much of the global temperature spike.
That area warmed 0.4°C in just 10 to 14 days, which is highly unusual, Karnauskas said.
Part of that area is clearly a brewing El Niño, which scientists may confirm in the next couple months and they can see it gathering strength, Karnauskas said. But the area in the Indian Ocean is different and could be a coincidental independent increase or somehow connected to what may be a big El Niño, he said.
“We’re already starting at such an elevated background state, a baseline of really warm global ocean temperatures, including in the tropical Pacific and Indian Ocean. And suddenly you add on a developing El Niño and now we’re like off the chart,” Karnauskas said.
Massive Ocean Warming
It’s been about seven years since the last El Niño, and it was a whopper. The world has warmed in that seven years, especially the deeper ocean, which absorbs by far most of the heat energy from greenhouse gases, said Sarah Purkey, an oceanographer at the Scripps Institution for Oceanography. The ocean heat content, which measures the energy stored by the deep ocean, sets new record highs each year regardless of what’s happening on the surface.
Since that last El Niño, the global heat ocean content has increased .04°C (.07°F). That may not sound like a lot, but “it’s actually a tremendous amount of energy,” Purkey said. It’s about 30 to 40 zettajoules of heat, which is the energy equivalent of hundreds of millions of atomic bombs the size that leveled Hiroshima, she said.
On top of that warming deep ocean, the world had unusual cooling on the surface from La Niña for three years that sort of acted like a lid on a warming pot, scientists said. That lid is off.
“La Niña’s temporary grip on rising global temperatures has been released,” NOAA oceanographer Mike McPhaden told AP in an email. “One result is that March 2023 was the second-highest March on record for global mean surface temperatures.”
If El Niño makes its heavily-forecasted appearance later this year, “what we are seeing now is just a prelude to more records that are in the pipeline,” McPhaden wrote.
Karnauskas said what’s likely to happen will be an “acceleration” of warming after the heat has been hidden for a few years.
The main body of this story was first published by The Associated Press and republished by The Canadian Press on April 20 and 27, 2023.
