Tuesday, July 23

The ocean is hotter than ever—what happens next? 2023

Early April saw a new worldwide ocean temperature record of 21.1 oC, 0.1 oC higher than March 2016. Although stunning, the figure (see ‘How the ocean is warming’) is consistent with climate change-induced ocean warming. Its appearance before the El Niño climatic phenomenon that is projected to bring warmer, wetter weather to the eastern Pacific later this year is extraordinary.

That implies warmer-than-average ocean temperatures will continue or worsen, bringing more severe weather and marine heatwaves that harm reefs and whales.

An oceanographer at NASA’s Jet Propulsion Laboratory in Pasadena, California, Josh Willis predicts a year of record highs. If El Niño takes off, this year will be crazy.

ENSO is a natural climatic cycle. El Niño weakens or reverses Pacific winds, enabling warm seas to flow east. El Niño brings warmer ocean and land temperatures. During a strong El Niño, the previous record was 21.0 oC.

After an unusual three-year La Niña episode, ENSO is neutral. The World Meteorological Organization predicts a 60% possibility of El Niño between May and July and an 80% chance by October this year.

The Blob returns

Andrew Leising, an oceanographer at NOAA’s Southwest Fisheries Science Center in La Jolla, California, forecasts exceptionally warm Pacific seas along the west coast of the US in summer and fall. He says, “this could create a situation like 2014 to 2015, when we got smacked by the Blob heatwave,” a massive oceanic heatwave.

Marine heatwaves harm fisheries and animals. Leising says large heatwaves on the US Pacific coast compress the habitable zone for many species into a tiny band. That can increase ship collisions and fishing gear entanglements when whales pursue food closer to shore.

He adds that algal blooms can block crab and mussel harvests when warm waves meet the beach. Leising thinks that exceptionally high upwelling of cold water around the US west coast might prevent warming this year.

Huang said seas along Peru’s coast and in the Southern Ocean suffered marine heatwaves in February, leading up to April’s record ocean temperature.

Corals suffer in unusually warm seas. Matthew England, a physical oceanographer at the University of New South Wales in Sydney, Australia, reports high temperatures in most coral zones. Coral reefs are being pushed to severe temperatures and can’t rebuild because it doesn’t cool down.

The third-ever worldwide coral bleaching crisis occurred during 2016’s record-breaking ocean temperatures. Bleached corals lose their algae and perish.

Christian Voolstra, a coral researcher at the University of Konstanz in Germany, predicts another worldwide bleaching catastrophe this year. He adds that El Niño will arrive eventually, even if not this year. “It’s always bad.”

Heating planet

Warm seas retain less dissolved oxygen, stressing marine life. William Cheung, a marine biologist at the University of British Columbia in Vancouver, says ocean warming and deoxygenation are reducing species’ habitats.

High ocean temperatures cause severe weather. This year’s extremely warm seas off Peru have fed severe rains and Tropical Cyclone Yaku, the first such storm in decades.

The NOAA-recorded ocean temperature spike—likely the biggest in over 100,000 years—coincides with other warming patterns. In February 2023, southern hemisphere sea ice extent reached a record low. Global warming heats the water by 90%. Water is harder to heat than air, thus its surface temperature is rising more slowly.

“This wouldn’t have happened without climate change,” tweeted Woods Hole Oceanographic Institution ocean biogeochemical modeller Jens Terhaar. Extremes are now normal.

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