The world’s oceans have suddenly become much warmer and well above record levels in recent weeks, with scientists scrambling to understand what that means and whether it predicts a surge in atmospheric warming.
Some researchers think the jump in sea surface temperatures comes from a brewing and possibly strong natural El Nino warming weather condition, plus a rebound from a three-year cooling La Nina, all on top of the steady global warming that’s going on. heating the deeper water below. If so, they said, record-breaking ocean temperatures this month could be the first of many heat records to be broken.
From early March to this week, the global average sea-ocean surface temperature increased by nearly two-tenths of a degree Celsius (0.36 degrees Fahrenheit), according to the University of Maine’s Climate Reanalyzer, which climate scientists they use and trust. That may seem like a small amount, but for the average world’s oceans — which is 71 percent of land area — to grow that much in such a short time, “that’s huge,” said Kris Karnauskas, a climate scientist at the University of Colorado. “This is an amazing departure from what was already a hot state to begin with.”
Climate scientists have been talking about the warming on social media and with each other. Some, like Michael Mann of the University of Pennsylvania, are quick to dismiss concerns by saying it’s simply a growing El Nino on top of a steady increase in human-caused warming.
It warmed especially off the coasts of Peru and Ecuador, where most El Ninos started before the 1980s. El Nino is the natural warming of parts of the equatorial Pacific that changes the weather around the world and raises global temperatures. Up until last month, the world has been on the receiving end of a cooling called La Nina, which was unusually strong and long, lasted three years, and caused extreme weather.
Other climate scientists, including National Oceanic and Atmospheric Administration oceanographer Gregory C. Johnson, say it doesn’t appear to be just El Nino. There are several marine heatwaves or oceanic warming spots that don’t fit an El Nino model, such as those in the North Pacific near Alaska and off the coast of Spain, he said.
“This is an unusual pattern. This is an extreme event on a global scale” in areas simply not adapting to an El Nino, said Gabe Vecchi, a climate scientist at Princeton University. “This is a huge, huge sign. I think it will take some level of effort to figure this out.
The University of Colorado’s Karnauskas took global sea surface temperature anomalies over the past few weeks and subtracted year-to-date average temperature anomalies to see where the sudden burst of warming is strongest. He found a long stretch across the equator from South America to Africa, including the Pacific and Indian oceans, responsible for much of the global temperature spike.
That area warmed by four-tenths of a degree Celsius in just 10 to 14 days, which is highly unusual, Karnauskas said.
Part of that area is clearly a brewing El Nino, which scientists could confirm in the next couple of months and can see it gather strength, Karnauskas said. But the area in the Indian Ocean is different and could be a random independent rise or somehow related to what could be a major El Nino, he said.
“We’re already starting from such a high background state, a baseline of really warm global ocean temperatures, including in the tropical Pacific and Indian Oceans. And all of a sudden you add a developing El Nino and now we’re like off the charts,” Karnauskas said.
It’s been about seven years since the last El Nino, and it was a blockbuster. The world warmed in those seven years, especially the deepest ocean, which absorbs by far the most heat energy from greenhouse gases, said Sarah Purkey, an oceanographer at the Scripps Institution for Oceanography. Ocean heat content, which measures the energy stored by the deep ocean, sets new records every year regardless of what happens on the surface.
Since the last El Nino, the global ocean’s heat content has increased by 0.04 degrees Celsius (0.07 degrees Fahrenheit), which may not sound like much but “it’s actually a huge amount of energy,” he said Purkey. That’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.
In addition to deep ocean warming, the world has experienced unusual surface cooling from La Nina for three years that acted like a lid on a heated pan, the scientists said. That lid is off.
“La Nina’s temporary grip on rising global temperatures has been released,” NOAA oceanographer Mike McPhaden said in an email. “One result is that March 2023 was the second-highest March on record for global mean surface temperatures.”
If El Nino makes his heavily anticipated appearance later this year “what we’re seeing now is just a prelude to more records that are in the pipeline,” wrote McPhaden.
Karnauskas said what is likely to happen is an “acceleration” of warming after the heat has been hidden for a few years.
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