Science Snippets: Acidification Milestone Passed

Draft script:

If you have completed a high school chemistry class, then you probably remember the importance of acidity for various aspects of our lives. Today’s example comes from the oceans of the world. Marine life evolved via natural selection to a specific environment, including a narrow range of acidification.

From Dialogue Earth on 23 December 2025 comes a story titled Explainer: The latest science on ocean acidification. Here’s the subhead: “In 2025, scientists warned the ‘planetary boundary’ for ocean acidification had been crossed. This is what that means and why it matters.” Here’s the lede: “The past twelve months have been worrying for researchers who study the chemistry of the ocean.”

The following two paragraphs explain what’s happened and why it matters: “More and more evidence has been published showing that human activities are fundamentally altering this chemistry in an acidic direction.

At the end of 2025, it seems clear ocean acidification is pushing the largest habitat on Earth into a risky zone.”

The first of nine subsections provides an explanation for the importance of this matter. It is titled “How does CO2 in the atmosphere make the ocean acidic?”

The explanation is provided in four short paragraphs: “Ocean acidification is part of the global carbon cycle.

When carbon dioxide dissolves in water, it forms carbonic acid. This acid releases hydrogen ions, which lower the seawater’s pH balance.

Carbon dioxide emitted by human activities may be largely released into the atmosphere, but it does not all stay there. Huge amounts are absorbed by the ocean. A study published in 2023 determined that the ocean absorbed 25% of anthropogenic CO2 emitted from the early 1960s to the late 2010s. This has so far saved humanity from greater global warming.

Because of the rise in atmospheric CO2 concentrations over the past century, more CO2 has been taken up by the ocean, causing it to acidify.”

The next subsection asks and answers the question “How acidified is the ocean as of 2025?”

“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 ... 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 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.”

The following asks and answers the question “Why does this matter?”

“In May, a new study found that as acidification intensifies, the ocean’s capacity to absorb atmospheric CO2 weakens, reducing its ability to slow global warming. The explanation lies in chemistry: as the sea accumulates more carbon dioxide, its ‘carbonate buffering’ capacity is reduced, making CO2 more chemically challenging to absorb.

In March, researchers reported that the speed at which people are releasing CO2 into the atmosphere is much faster than the ocean’s natural capacity to absorb it without becoming acidic. This is profoundly altering the ocean’s chemistry. The consequences of the change are not yet fully clear.”

I’ll skip a subsection about ocean animals with shells to address a subsection that concerns us: “Do we need to worry about humans and other animals, too?” You almost certainly know the answer to this question, but I’ll include the five paragraphs of explanation: “While calcifiers are the first to suffer the consequences of a more acidic ocean, many other species, including humans, are set to pay the price if we continue on this trajectory. Upcoming research areas are focusing on the impact of changes in ocean chemistry on non-calcifying organisms.

In a summary about the ‘silent crisis’ of ocean acidification published in April, experts from Spain’s Institute of Marine Sciences (ICM) highlight how data collected over recent decades is demonstrating that non-calcifying species, such as fish and squid, are suffering from impaired respiration, altered behaviour and reduced reproductive success in a more acidic environment.

The behavioural impacts are thought to be due to calciferous structures within fish ears that, like corals, cannot form properly in environments that are too acidic. This correlates with diminishing behavioural responses to danger. However, these are preliminary studies that focus on one generation of marine creatures only. More research in the field is needed.

Two other studies published this year, one observed in the Pacific and the other in the Mediterranean, found that the development and survival of mollusc larvae are negatively impacted by lower pH levels. A reduction in the number and characteristic variations of adult species was detected.

Though a direct correlation between increasingly acidic oceans and human health has not yet been explored, more than a billion people worldwide depend on healthy coral reefs for food and coastal protection. If these reefs become more fragile because they cannot properly build calcium shells, this will generate cascading problems. An acidic ocean will mean millions of dollars in lost fisheries and tourism revenue, because frailer coastal reefs will not provide the same level of coastal protection from storms.”

The next subsection is titled “What is the ocean acidification planetary boundary?” The first paragraph provides the dire and expected information: “Perhaps the biggest news in ocean acidification this year is the warning that a new ‘planetary boundary’ has been crossed.”

The importance of this issue is great. Passing planetary boundaries is critical to the continued existence of all life on Earth. A researcher at the University of St. Andrews’ School of Earth and Environmental Sciences in Scotland provides the expected and incorrect response to this information: “We know that the planet will find a way to survive. The question is if humanity will cope with the transition.”

If you’ve been paying attention to my work, which relies on the work of other scholars, then you know that the planet will not necessarily find a way to survive. A paper published in Scientific Reports, part of the renowned Nature series of peer-reviewed publications, concluded on 13 November 2018 that all life on Earth likely would go extinct during the ongoing Mass Extinction Event. That was nearly eight years ago. Concluding that “we know that the planet will find a way to survive” and seriously questioning “if humanity will cope with the transition” express unsupported optimism.

Humans are relatively large animals with little protection from myriad factors that threaten our species with extinction. Expressing optimism about our ability to survive is unwarranted. I would love to have our species and many others survive the ongoing Mass Extinction Event. If only wishing would make it so.