The World’s Oceans Broke A Heat Record… Again

Those higher temperatures could lead to more coastal erosion, flooding, and extreme weather

By Avery Schuyler Nunn, Grist

The temperature of the planet’s oceans soared to a third consecutive record last year, something oceanographers and climatologists consider a critical indicator of a warming world and an accelerant of extreme weather.

A study published Wednesday in Advances in Atmospheric Sciences found the level of heat contained in the sea reached its highest level since record keeping began in 1958.  Data indicate that the top 2,000 meters gained about 10 zettajoules of heat between 2021 and 2022 — an amount equivalent to about 100 times the world’s electricity generation in 2021.

The news follows a report, released Tuesday, that found the past eight years were the hottest in recorded history. As dire as that sounds, the oceanic data is more troubling still because marine temperatures are far less variable than atmospheric temperatures and provide a clearer picture of how the world is warming.

Oceans, which cover more than 70 percent of the planet’s surface, absorb the majority of the solar energy that reaches Earth as sunlight. The rest is reflected back into space. As increasing emissions trap more and more of it here at home, with about 93 percent remaining in the sea. The epipelagic zone — which runs to a depth of about 200 meters — now stores as much heat as the atmosphere, limiting its ability to help regulate planetary temperatures. Warming seas lead to more frequent, and extreme, hurricanes, typhoons and rainstorms of the sort California is experiencing this month.

All that heat also causes oceans to rise by melting Arctic and Antarctic ice sheets and also by causing the molecules within sea water to move ever so slightly apart, increasing their volume. NASA attributes almost 40 percent of global sea level rise to this phenomenon, called thermal expansion, resulting in coastal erosion, flooding, and the loss of wetlands and marshes.

Rising global temperatures have been somewhat tempered by three successive years of La Niña, a period of lower-than-normal marine surface temperatures. The impending return of El Niño, when the opposite occurs, could lead to further increases.

“The long-term trends are very clear,” Gavin Schmidt, director of the NASA Goddard Institute for Space Studies told the Wall Street Journal in a statement. “They are not due to natural variation. They are not due to the sun. They are not due to volcanoes. They are due to our emissions of greenhouse gasses and as long as we continue to emit large amounts of greenhouse gasses, these trends will continue.”