Ocean Heat, Sea Surface Temperatures Shattered Records in 2023

2023, the hottest year on record overall, was also the hottest year on record for the world's oceans.

A study published Thursday in Advances in Atmospheric Sciences found that the upper 2,000 meters of the ocean warmed by 15 zettajoules in 2023 compared to 2022, according to one dataset. To put that in perspective, the world's economy only requires half a zettajoule to run every year, the Chinese Academy of Sciences explained in a statement. Fifteen zettajoules would be enough to boil 2.3 billion Olympic-sized swimming pools or roast 260 trillion turkeys.

"The ocean is the key to telling us what's happening to the world, and the data is painting a compelling picture of warming year after year after year," study co-author John Abraham, a professor at the University of St. Thomas in Minnesota, toldThe Guardian.

Ocean heat content has been on the rise since the late 1950s, and, for the past decade, each year has been the warmest on record, according to the Chinese Academy of Sciences.

The ocean is an important indicator of human-caused climate change because around 90% of the excess heat produced by the burning of fossil fuels is absorbed by its top 2,000 meters, according to United Press International.

"As long as the level of greenhouse gases remains relatively high in the atmosphere, the oceans will keep absorbing energy, leading to the increase of the heat in the oceans," study lead author Cheng Lijing, an oceanographer at the Institute of Atmospheric Physics (IAP) at the Chinese Academy of Sciences in Beijing, toldNature.

"We're already facing the consequences and they will get far worse if we don't take action."

The study was the latest in a yearly effort led by the IAP; this year's installment had contributions from 34 scientists in 19 research bodies in China, France, Italy, New Zealand, and the U.S., according to Nature and the Chinese Academy of Sciences. The researchers looked at two datasets for ocean heat content: the IAP's dataset and one compiled by the National Centers for Environmental Information (NCEI) of the National Oceanic and Atmospheric Administration (NOAA).

The 15 zettajoules figure came from the IAP dataset, while the NOAA dataset gave a lower increase of nine zettajoules. Lijing explained on social media that both organizations used the same raw data, but had different methods of quality control and spatial interpolation. Sometimes, accurate high temperature measurements can be mistakenly discarded as inaccurate, the Chinese Academy of Sciences pointed out.

"This means that the warming might be greater than the numbers reported here," Lijing said in a statement.

NCEI oceanographer and study co-author Tim Boyer told Nature that "the important point in the paper and for scientific understanding is that the ocean is warming consistently, year over year to new record levels of ocean heat content."

In addition, the paper documented a record rise in sea surface temperature. It was higher than 2022's by 0.23°C for the entire year and by what the authors called an "astounding" 0.3°C for the second half of the year.

Another measurement that reached record levels in 2023 was ocean stratification, which occurs when the warmer water floats near the surface and does not mix as much with the cooler water below, The Guardian explained. This can harm ocean life by reducing the amount of oxygen available to it. It also decreases the ocean's ability to absorb both heat and carbon dioxide.

Another point raised by the study authors is that what happens to and in the ocean does not stay in the ocean.

"Ocean warming has far-reaching consequences on physical, human, and biological systems in the Earth system, which is expected to be much more severe in the future because of the irreversibility of ocean warming in the following centuries," Lijing wrote on social media.

Warmer oceans increase sea-level rise, fuel extreme weather events such as storms or droughts, and impact marine life by forcing some animals to move in search of cooler waters or changing the time when migrations or reproduction occur, Nature explained.

"We're already facing the consequences and they will get far worse if we don't take action," Abraham told The Guardian. "But we can solve this problem today with wind, solar, hydro, and energy conservation."

"Once people realize that, it's very empowering," Abraham continued. "We can usher in the new energy economy of the future, saving money and the environment at the same time."