Though 2020 saw a record drop in global carbon emissions, it wasn’t enough to stem the rapid warming of our oceans. Once again, ocean temperatures have hit a record high, meaning in 2020 the world’s oceans were the warmest they’ve ever been. In that year alone, the upper part of our oceans absorbed 20 more zettajoules than in 2019—an amount of heat that could boil 1.3 billion kettles.
A study published in Advances in Atmospheric Sciences and authored by an international team of 20 scientists from 13 institutions details this uptick in ocean warming and includes a plea to policymakers to mitigate the situation before it gets worse. More than 90% of the excess heat due to global warming is absorbed by the ocean, the researchers say, but our oceans’ response takes some time to manifest. That means ocean temperatures will keep getting warmer for “at least several decades,” and that we need to make changes to human-caused global warming now to prevent even worse warming in the future.
The study calculated the ocean temperatures down to 2,000 meters below the surface using data from measurement devices from the World Ocean Database, a project by the National Oceanic and Atmospheric Administration and the National Center for Environmental Information.
As the ocean warms, there are consequences for humans and other natural systems on our planet. Warmer oceans, along with a warmer atmosphere, bring about more intense storms—particularly typhoons and hurricanes—and increase the risk of flooding. With so much heat trapped in the ocean, the ocean will also release that energy, warming up our atmosphere. Extreme fires such as those in Australia and the American West throughout 2020 will become more common, the researchers say.
This latest report builds on one that the same lead author, Lijing Cheng, professor at the Institute of Atmospheric Physics, published last year. In 2019, that previous report found, the ocean temperature was about 0.075 degrees Celsius warmer than the average temperature from 1981 to 2010. Though a seemingly small increase, it means the oceans have taken in 228,000,000,000,000,000,000,000 joules—that’s 228 sextillion—of heat, equivalent to the energy released by 3.6 billion Hiroshima atom bomb explosions.
In 2020, the most recent report found, the upper 2,000 meters of the world’s oceans absorbed 20 zettajoules—a unit of energy equivalent to a sextillion joules—more than it did in 2019.
Why isn’t the ocean boiling? It’s only because of how vast it is, Cheng says in a statement, which highlights how much energy the ocean can absorb and how big an impact on the environment it will have as it releases it. That also shows why we need to pay special attention to the oceans as more countries pledge to reach carbon neutrality. “Any activities or agreements to address global warming must be coupled with the understanding that the ocean has already absorbed an immense amount of heat, and will continue to absorb excess energy,” Cheng writes, until we reach a point where the carbon levels in our atmosphere are significantly lower.