Environmental Science
Ocean Acidification
Quick fact
Since the Industrial Revolution, ocean acidity has increased by about 30% (a 0.1 drop in pH), a rate of change 100 times faster than any natural variation in the last 50 million years.
Why this is interesting
The ocean has absorbed about 30% of the carbon dioxide we've emitted—but this vital service comes at a hidden cost that threatens marine life from the bottom up.
Read the full explanation
Understanding Ocean Acidification
When carbon dioxide from the atmosphere dissolves into seawater, it reacts with water to form carbonic acid, which then breaks apart into hydrogen ions and bicarbonate. This increase in hydrogen ions lowers the water's pH, making it more acidic—like adding a squeeze of lemon to a glass of water. The extra hydrogen ions also grab onto carbonate ions, which are vital for creatures like corals, clams, and some plankton to build their hard shells and skeletons. With fewer carbonate ions available, these organisms struggle to grow and maintain their structures, weakening entire marine food chains.
A deeper explanation
The underlying chemistry involves a series of equilibria: CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻ ⇌ 2H⁺ + CO₃²⁻. The influx of CO₂ shifts these equilibria to produce more hydrogen ions, which combine with carbonate ions to form bicarbonate. The resulting decrease in carbonate ion concentration raises the saturation horizon—the depth at which calcium carbonate dissolves—making it harder for calcifying organisms to form their shells. This phenomenon is not just a chemical curiosity; it directly threatens coral reef ecosystems, shellfish industries, and the entire oceanic food web. As acidification progresses, it also reduces the ocean's ability to absorb future CO₂, creating a feedback loop that exacerbates climate change.