Ocean acidification

What it is

The map is the change in OceanSODA-ETHZ v2025 surface pH on the total scale, from the 1985-1989 mean to the 2020-2024 mean, published through NOAA NCEI OCADS. A negative number is acidification. The longer figure used on this site, about 0.1 pH units of open-ocean decline since about 1750, still comes from IPCC AR6 and the NOAA PMEL Carbon Program. The NOAA Ocean Acidification Program describes the observing network behind that longer record.

Why it is on this shelf

Currents, salinity, surface temperature, and pollution answer other questions. This card is the recent change in surface pH. It is not a sea-surface temperature map and not a map of plastic, oil, or coastal hypoxia.

How to read it

The colour is the change in pH, not the pH itself. The open ocean is still alkaline; the shift matters for calcifying organisms and for carbonate minerals. Coastal water can add local nutrient and upwelling signals on top of the global uptake of carbon dioxide. NOAA’s Ocean Acidification Program and the PMEL Carbon Program explain the observations behind the long-term figure.

Sources

• NCEI OCADS: OceanSODA-ETHZ v2025 (accession 0220059)
• NOAA Ocean Acidification Program: hub
• NOAA OAP: What is ocean acidification?
• NOAA PMEL Carbon Program: Ocean Acidification
• NOAA PMEL Carbon Program: hub
• NOAA PMEL: Observations and Data
• NOAA PMEL: Hydrographic Cruises
• NOAA PMEL: Consensus OA trend assessments
• NOAA PMEL: Buoys and Autonomous Systems
• NCEI: Ocean Carbon & Acidification Data System (OCADS)
• Copernicus Marine: data access (optional secondary)
• Copernicus Marine: product catalogue (optional)

Open source map →