Ocean Acidification: The Chemistry Nobody Talks About Enough

# Ocean Acidification: The Chemistry Nobody Talks About Enough

Ocean acidification is one of the most underreported aspects of climate change. It doesn't have the dramatic visibility of sea level rise or extreme weather — it's a chemical change happening below the surface at pH scales that are difficult to intuit. But its biological consequences are profound and, in some respects, less reversible than temperature-related effects.

When CO2 dissolves in seawater, it doesn't just stay dissolved. It reacts with water to form carbonic acid, which then dissociates to bicarbonate ions and hydrogen ions. More hydrogen ions means lower pH — that's what "acidification" means chemically. The ocean's average pH has dropped from roughly 8.2 to 8.1 since the industrial revolution. That sounds small. It isn't. pH is a logarithmic scale: a 0.1 unit drop represents about a 26% increase in hydrogen ion concentration.

The immediate problem is with organisms that build shells or skeletons from calcium carbonate: oysters, mussels, sea urchins, corals, pteropods (tiny ocean snails that form the base of polar food webs). As acidity increases, calcium carbonate structures dissolve more easily. Below a threshold called the *saturation horizon*, calcium carbonate doesn't form at all. That horizon is shoaling — moving upward toward the surface — as acidification progresses.

Pteropods in the Southern Ocean are already showing shell dissolution in wild-caught specimens. Coral reefs — which support roughly 25% of all marine species despite covering less than 1% of the ocean floor — are threatened by the combination of warming (bleaching) and acidification (reduced calcification). Some researchers believe we're already past the point where coral reefs as we currently know them can be preserved under most warming scenarios.

**The reason ocean acidification is especially concerning from a systems perspective:** it operates on a different timescale than temperature. We can remove carbon from the atmosphere, in principle — it would take centuries, but the system would eventually respond. The deep ocean's chemistry changes on timescales of thousands of years. Some of the acidification damage to marine ecosystems is functionally irreversible on any planning horizon that matters to living humans.

Ocean Acidification: The Chemistry Nobody Talks About Enough

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