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Ocean acidification refers to the drop in seawater pH that occurs as the ocean absorbs carbon dioxide released into the atmosphere by human activity. In this article, we'll walk through the causes and impacts of ocean acidification, how the international community is responding, and what actions we can take ourselves.

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By 2050, the Ocean Could Turn
as Acidic as a Soft Drink

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"At this rate, the ocean could become as acidic as cola." That's an actual warning from scientists. It might sound like an exaggeration at first, but once you break down the chemistry, you'll find the comparison is unsettlingly precise.

Picture this: what happens if you leave a tooth soaking in a glass of cola? The carbonic acid slowly eats away at the tooth's hard enamel until it softens and erodes. Right now, across the entire global ocean, a strikingly similar chemical reaction is playing out.

The carbon dioxide pouring out of smokestacks and tailpipes doesn't just linger in the atmosphere. A large share of it dissolves into seawater, forming carbonic acid (H₂CO₃), which then releases hydrogen ions (H⁺). As hydrogen ions build up, the ocean's pH drops, and the water shifts steadily toward the acidic end of the scale.

And the problem doesn't stop there. This same process depletes carbonate ions in seawater — the very building block that shell-forming creatures like corals and mollusks rely on to construct their bodies and skeletons. When that raw material runs short, these organisms struggle to build shells at all, or worse, the shells they've already built begin to dissolve.

This is a far bigger problem than a single decaying tooth. It means the very "skeleton" holding up the entire ocean ecosystem is quietly dissolving as we speak. As a result, the ocean's ecological balance is being pushed toward collapse — and faster than most of us realize.

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What Is Ocean Acidification?

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Let's take a quick trip back to chemistry class. pH is measured on a scale from 1 to 14 — the lower the number, the more acidic; the higher, the more alkaline (basic). But here's the catch: this isn't a simple linear scale, it's logarithmic. That means every single point drop in pH represents a tenfold increase in acidity.

Over the past 40 years, the ocean's average pH has been steadily falling. On paper, the change looks tiny — just a couple of decimal points. But once you factor in the logarithmic scale, the picture changes dramatically. The pre-industrial average ocean pH was 8.21; today it has dropped to 8.10. That may look like a modest 0.1 shift, but it actually represents roughly a 30% increase in ocean acidity.

What's even more alarming is the speed. Scientists say the current pace of acidification is unlike anything seen in millions of years of Earth's history. Marine life simply hasn't had time to adapt — the change is arriving far faster than evolution can keep up.

Average ocean pH fell from 8.21 pre-industrial to 8.10 as of 2023, while the 2023-2025 fourth bleaching event affected 84% of reef area across 83 countries.

Source: NOAA, IPCC AR6

Over the past 40 years, the pH level has been steadily decreasing — in other words, the ocean is becoming more and more acidic.

© Nicolas Gruber & Luke Gregor

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Coral Bleaching —
The Ocean's Distress Signal

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Ever heard of "coral bleaching," where coral turns ghostly white? Corals themselves are actually translucent or white by nature. The vibrant colors we see in photos come from zooxanthellae — tiny algae living inside coral tissue in a mutually beneficial partnership. The algae photosynthesize and share nutrients with the coral, and in return, the coral offers them a safe home. It's a textbook symbiosis.

But when the water becomes too warm or too acidic, this age-old partnership breaks down. Stressed corals expel the algae living inside them. Once the algae are gone, the coral loses its color, leaving only a stark white skeleton behind — like the bare frame of a newly built structure with no walls. If this condition persists, the coral eventually starves to death. Bleaching is essentially the coral's last distress signal before it dies.

Australia's Great Barrier Reef, the largest coral reef system in the world, has already suffered this fate firsthand. In just two years, from 2016 to 2017, over half of its corals turned white and died. A living formation so vast it's visible from space lost half of itself in just 24 months.

Source: Annual Summary Report on the Great Barrier Reef (2022)

If the story had ended there, it would almost have been a relief. But an even larger event followed. From January 2023 through mid-2025, NOAA confirmed the fourth global coral bleaching event — the fastest and most extensive on record. This time it wasn't confined to Australia. Bleaching-level heat stress impacted roughly 84% of the world's reef area across 83 countries, surpassing the third event (2014-2017, about 68%) as the largest on record. NOAA declared the event effectively concluded in mid-2025 — but the scale is too large to feel like relief.

Put simply: the Great Barrier Reef example is now just one case within four recorded global bleaching events. And those four events — in 1998, 2010, 2014-17, and 2023-25 — have each broken the previous record, like four alarm bells ringing louder and more urgently each time.

From 20% in 1998, to 35% in 2010, to 68% in 2014-17, to 84% in 2023-25 — each global coral bleaching event has been larger than the last.

Source: NOAA Coral Reef Watch, ICRI

You might wonder why coral reefs matter so much. Reefs cover less than 1% of the ocean floor, yet an astonishing one-quarter of all marine species depend on them to survive. That's exactly why coral reefs are often called "the rainforests of the sea."

When a reef collapses, everything built on top of it — spawning grounds, shelter, entire food chains — collapses along with it. And the ripple effects reach far beyond the water, touching the millions of people whose livelihoods depend on reef-based fishing and tourism.

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Shellfish and Fish Aren't
Safe Either

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Coral reefs aren't the only ones in trouble. At oyster hatcheries along the U.S. Pacific coast, something troubling has been happening for years. When acidified seawater flows in, newly hatched baby oysters struggle to form proper shells, leading to repeated mass die-offs. For oyster farmers, it's a livelihood at stake — and for the rest of us, it's a preview of what could happen to the seafood on our plates.

Even the very bottom of the ocean food chain isn't spared. Pteropods — tiny swimming snails nicknamed "sea butterflies" — are a key food source for krill and small fish. Experiments have confirmed that in acidified seawater, their delicate shells slowly dissolve away. When the foundation of the food chain crumbles, everything stacked on top of it — small fish, tuna, and eventually our own dinner tables — starts to wobble too.

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The International Community
Hasn't Stood Idle

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Fortunately, humanity isn't simply watching this crisis unfold. The ocean has no borders, and there's growing recognition that the response to its acidification needs to cross borders too.

A prime example is the OARS (Ocean Acidification Research for Sustainability) program. OARS systematically studies how ocean acidification affects marine life and ecosystems, and provides data and strategic guidance to help policymakers around the world take action. In short, it pulls together scattered observation data from across the globe into one place, so we can finally see the full picture of the ocean's condition.

This data has already proven its power in the real world. Tuvalu, a small island nation in the South Pacific, sits mostly just a few meters above sea level. Rising seas and ocean acidification together threaten the very existence of the country. Tuvalu has used data from programs like OARS to make its case at the United Nations — turning raw statistics into evidence for a nation's survival. In the halls of powerful nations, data was one of the strongest weapons a small island state had.

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What We Can Do Is Closer
Than You Think

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At its root, ocean acidification comes down to one thing: carbon dioxide. Which means the solution ultimately comes down to cutting emissions. But this isn't a problem either side can solve alone — it takes both international action and individual effort, moving together.

This might sound like a big ask, but honestly, more than half of this list is something you could start today. The ocean has long been our planet's silent shield, quietly absorbing much of the carbon dioxide humanity has released and keeping global temperatures in check. Now it's our turn to protect that shield in return.

"How much more must we lose on this planet before we finally act?"

A future where the ocean turns as acidic as cola is not yet written in stone. The bleached white skeletons of coral, the empty shells at oyster farms — these are still stories we can rewrite.

What we choose to do now will shape the color of the ocean future generations inherit. And that choice doesn't belong only to governments and corporations far away — it starts with what we drive, what we eat, and what we choose to speak up about, today.

“Ocean acidification is another climate crisis caused by human activity.

The ocean is changing quietly — but surely — while we remain unaware.”

— From a report by the Intergovernmental Oceanographic Commission (IOC) under UNESCO

Written by Sharon Choi

Director of Planning

Sunhak Peace Prize Secretariat