—

Ocean pH is still above 7 (basic) — but it is becoming less basic as the sea absorbs CO₂.

—

The Keeling Curve — the atmosphere changing the ocean

Charles David Keeling’s Mauna Loa record is the source line: as atmospheric CO₂ rises, seawater absorbs more of it and surface pH falls.

CO₂ and ocean pH since 1958

Atmospheric CO₂

Modelled surface pH modelled

Each bar is one year. Top: Mauna Loa CO₂ (ppm). Bottom: global surface pH modelled from that CO₂ (Doney et al. 2009).

Ocean pH scale

—

ppm (latest daily)

—

<1 = corrosive

—

stations on alert

What does acidification do to life?

Pteropods: shells of these sea snails are already dissolving in parts of the Southern Ocean.

Corals: skeleton formation slows as aragonite becomes harder to pull from seawater.

Oyster hatcheries: Oregon and Washington farms had to buffer intake water after larval die-offs.

Where is acidification fastest?

Three open-ocean reference stations where scientists have measured pH continuously for decades — Hawaii Ocean Time-series (HOT, off Hawaii), Bermuda Atlantic Time-series (BATS), and the European Station for Time-series in the Ocean (ESTOC, off the Canary Islands). The Δ/decade number is how much pH falls every ten years. A drop of −0.018 pH/decade sounds tiny but compounds: at this pace, the ocean becomes about 4% more acidic every ten years, and ~50% more acidic in a century. These are compiled literature trends, not live sensor readings.

GOA-ON & IOOS stations

Station	Type	pH	Ω_arag	Δ/decade	Alert

How does this look in 2050 and 2100?

IPCC AR6 central projections under three emissions futures — SSP1-2.6 (Paris-aligned, low emissions), SSP2-4.5 (middle, slow progress), and SSP5-8.5 (high, fossil-heavy). Two columns per year: pH (the acidity scale — lower = more acidic) and Ω_arag (aragonite saturation — a chemistry value that has to stay above ~1 for shells to form. Tropical reefs typically need Ω above ~3). Below ~1, shells dissolve faster than they form.

Emissions future	2050 pH	2050 Ω_arag	2100 pH	2100 Ω_arag

What drives this

Climate pollution →Human CO₂ emissions raise the atmospheric concentration the ocean absorbs.
Ocean heat →Warming and chemistry interact: heat stresses ecosystems while CO₂ changes carbonate balance.

What this drives

Coral bleaching →Acidification weakens reef building while heat drives bleaching.
Food systems →Shellfish and fisheries are part of the same climate-food risk chain.

How we know this

Source: NOAA GML Mauna Loa CO₂ (live download) + Doney et al. 2009 pH model; station and projection tables from peer-reviewed literature and IPCC AR6.
Update cadence: CO₂ refreshes daily from NOAA public files; modelled pH moves with CO₂; station and IPCC values are manual reference data (yearly at most).
Time coverage: Keeling record from 1958; modelled pH aligned to that window; station mini-charts show ~30-year compiled trends.
Methods: Surface pH is modelled from atmospheric CO₂, not directly measured on this page. Open-ocean stations (HOT/BATS/ESTOC) are literature snapshots.
Uncertainty: pH is logarithmic — a 0.1 drop is ~26% more acidic. Model captures global mean trend, not local upwelling or river effects.
Limitations: Sparse observing outside subtropical gyres; impact icons are illustrative; ocean is still basic (pH > 8), not “acidic” in everyday language.
Primary data: NOAA Mauna Loa CO₂ · How this page is built