The Ocean Already 30% More Acidic Than In Preindustrial Era; Key Planetary Limit For Acidification Was Breached In 2020

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Earth’s ocean has become roughly 30% more acidic than it was in the pre-industrial age, according to data from the European Environment Agency published in October. A huge part of that seawater pH decrease has come in recent decades. Just before the industrial revolution began in around 1750, Earth’s mean surface seawater pH was 8.2. By 1985 it had fallen to 8.11. By 2024, it was down to 8.04. This data indicates that pH at the surface of the ocean will decline even further by 2100, by between 0.15 and 0.5, depending on how much emissions are curtailed.

Also in October, researchers working at the Norwegian University of Science and Technology (NTNU) authored a study of ocean acidification models to quantify the global ecological and economic consequences of future acidity rises. “If in the years to come we continue on the current emission level, our models show that for most regions the ocean is on a trajectory toward worst-case scenarios,” says Sedona Anderson, lead author of the paper.

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Perhaps the biggest news in ocean acidification this year is the warning that a new “planetary boundary” has been crossed. In 2009, a group of scientists led by Potsdam University in Germany set out what they named planetary boundaries – nine limits to systems that have kept Earth’s environment stable during human existence. This project has become the annual Planetary Health Check report. One of the nine boundaries it investigates is ocean acidification. This is measured via the levels of aragonite in the ocean. Aragonite is a form of calcium carbonate used by huge numbers of sea creatures to build their shells and skeletons. When the ocean acidifies, carbonate ions become less abundant, making shell formation more difficult.

When the nine planetary boundaries were first established, the “safe limit” for acidification was set at a 20% reduction in the ocean’s aragonite levels, known as “aragonite saturation state”, compared to pre-industrial conditions. This figure was met with scepticism by some researchers in the field, who felt it was too high. “When the scientific community saw the data in the first planetary boundaries report, it quickly became apparent that that was just a best guesstimate,” says Helen Findlay, a professor at Plymouth Marine Laboratory in the United Kingdom. In 2024, Findlay’s team reassessed those original thresholds. In a paper published in June 2025, the team concluded that the reduction in the ocean’s aragonite saturation state needed to be much lower than previously thought to keep the ocean healthy: around 10%, rather than 20%. The team estimated that by 2020, the global ocean was, on average, within the “uncertainty range of the ocean acidification boundary”. In other words, the boundary may have been crossed. The deeper into the ocean the researchers looked, the worse the findings were. At 200 metres below the surface, 60% of global waters already indicated acidification levels beyond the newly established safe limit.

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https://maritime-executive.com/editorials/researchers-say-the-oceans-have-passed-a-milestone-for-acidification