Why the ocean is cooking off the coast of Southern California

The waters off the Southern California coast are now approaching tropical temperatures found in parts of the balmy Caribbean Sea. 

On Wednesday, the Scripps Institution of Oceanography in San Diego recorded its highest ocean temperature ever, of 79.2 degrees Fahrenheit. Scientists have taken measurements off the marine institute’s pier for over a century, since 1916.

This easily broke the previous record of 78.8 Scripps’ measured last week. The chilled Pacific Ocean waters do warm up this time of year, but these unusual temperatures are still about 7 or 8 degrees above average. 

“It’s an extreme event,” Clarissa Anderson, a biological oceanographer at the Scripps Institution of Oceanography, said in an interview.

Like extreme heat events on land, these record-breaking temperatures at sea are largely propelled by weather but given a substantial boost by human-caused global warming. 

Some 95 percent of the accumulated heat that gets trapped by potent greenhouses gases in the atmosphere is absorbed into the oceans. Rocky, solid land, simply can’t absorb as much energy.

“Global warming is really ocean warming,” Josh Willis, an oceanographer at NASA’s Jet Propulsion Laboratory, said in an interview. “The heat being trapped is almost all in the ocean.”

The initial driver of Southern California’s heating event, however, was weather. A big mass of warm air, or a high pressure system, has settled over the region, which has curbed the strong winds that blow from the north, explained Willis. 

These winds usually push surface waters away from the coast, allowing cooler waters from the darker depths to well up.

Global warming is really ocean warming

“That process has turned off this year,” said Willis.

In short, stagnate surface waters, which also recently absorbed heat from California’s hottest-ever recorded month, were then boosted by another couple of degrees Fahrenheit of background warming — that extra heat being trapped in the ocean from climate change, explained Willis.

“That extra couple degrees is the difference between setting the record, and not,” said Willis. “It would still be really hot — but it wouldn’t be a record.”

Though large-scale marine heat waves have increased substantially since 1925, this event, while record-breaking, might be too small to earn the official title “marine heat wave.”

“This extreme is a local event that happened,” Emanuele Di Lorenzo, a marine scientist at the Georgia Institute of Technology’s School of Earth and Atmospheric Sciences, said in an interview.

“It’s not connected to a large-scale heat wave like in 2014 or 2015,” he said, referring to an unprecedented warming trend called “the warm blob” that stretched from Alaska to Mexico. 

Still, Southern California’s balmy oceans will likely stay warm for a while — much longer than terrestrial heat waves. 

Oceans aren’t “so easy to cool off,” said Di Lorenzo.

Average sea and land surface temperatures since 1880.

And life in these waters is now being impacted by the unusual warmth.

“Marine life is intimately connected with temperature,” said Scripps’ Anderson, noting that some life thrives in the warmth, and others don’t do well, or die. 

Kelp beneath the pier is already beginning to disintegrate, but jellyfish are proliferating. Perhaps, said Anderson, a bloom of algae is in store. 

Extreme heat events, whether large-scale or small, won’t just continue in the future. They’ll become more common as weather events are pushed into higher boundaries and beyond by the warming climate, said Di Lorenzo.

“In the coming years, we’ll see more of these record-breaking extremes,” he said.