For a very long time, the ocean has been helping the climate, mostly unnoticed. Roughly 25% of the carbon dioxide that human activity releases into the atmosphere is absorbed annually by the world’s seas. This massive, silent service is powered by basic physics and marine biology and doesn’t require infrastructure, subsidies, or political consent to work. The idea that this function will continue has formed the foundation of climate projections. It didn’t entirely in 2023.
Even scientists who had been observing ocean warming data for decades were taken aback by the regularity with which sea surface temperatures in non-polar ocean regions smashed records in 2023. During a year when the baseline was already high, the North Atlantic was especially unusual, running several degrees above historical averages for extended periods of time. The ecological effects—coral bleaching, disturbed migration patterns, and strained fisheries—were the clear immediate concern for marine biologists and climate scientists. Tho less obvious, the temperature anomaly also changed the ocean’s chemical interaction with the atmosphere.
Anyone who has ever opened a warm beverage can intuitively comprehend the physics involved. Compared to warm liquid, cold liquid can store more dissolved gas. Gas solubility decreases with increasing water temperature. The surface ocean’s ability to draw carbon dioxide from the atmosphere above it decreases with increasing temperature, and at very high temperatures, water that had previously been absorbing carbon may start releasing it. expelling gasses. The carbon exchange is reversed by the ocean.
The data from 2023 revealed that this was occurring in significant portions of the subtropical and subpolar parts of the Northern Hemisphere. During parts of a year when models predicted the reverse, the North Atlantic, which has historically been one of the more productive zones for ocean carbon uptake, was leaking CO2 into the atmosphere instead of absorbing it. The combined effect over non-polar waters resulted in a carbon absorption rate that was around 10% lower than what conventional climate models and historical trends had indicated for that time. The models had taken into account El Niño conditions, which have traditionally reduced ocean carbon uptake; nonetheless, the regional heating increased the effect beyond what the modeling had predicted.
A collection of internal ocean feedbacks that are not entirely understood and cannot be relied upon to function consistently in subsequent years kept the result from getting worse. In 2023, dissolved inorganic carbon in the top ocean layers was reduced by natural biological and physical processes, somewhat offsetting the decrease in absorption capacity caused by temperature. According to scientists, this is a muted result—the buffer held, at least in part. The most important concern for the researchers analyzing this data is whether the same barriers will remain in place as sea surface temperatures continue to rise.
In isolation, the 10 percent statistic seems reasonable. It is a directional concern. According to models, the ocean’s carbon uptake is comparatively constant across a variety of warming scenarios, with significant regional variability but no impending collapse. 2023 showed that the absorption behavior can deviate dramatically and in the wrong direction from what the models predict for sufficiently extreme sea surface temperature anomalies. The climate estimates that assume constant ocean carbon uptake become increasingly less accurate if that divergence increases with warming, and atmospheric CO2 accumulates more quickly than those projections suggest.
