Plenary 1: GOA-ON and ocean acidification: a global perspective

OA Week 2021, Plenary Session 1

GOA-ON Goal #1 – Improve our understanding of global OA conditions

Dr. Richard Feely, Senior Scientist, NOAA Pacific Marine Environmental Laboratory, USA


The ocean’s chemistry is changing due to the uptake of anthropogenic carbon dioxide (CO2) from the atmosphere. Over the course of the last 270 years, the global oceans have absorbed approximately160 ± 20 Pg C as carbon dioxide (CO2), which is roughly 25-32% of the total CO2 that has been released into the atmosphere by the combined effects of human activities. Upon exchanging with seawater at the air-sea interface, CO2 undergoes a chemical reaction with seawater to form carbonic acid which increases the hydrogen ion concentration of seawater in a process known as ocean acidification (OA). Since the late 1980s, surface ocean pH has decreased by a range of -0.07 to – 0.17 per decade, with measurable regional trends. The decline in pH generally decreases with depth within the ocean interior but temporal changes in acidification can be observed to depths as much as 2000 m below the surface. Current projections indicate that by 2100 the pH of the surface water is expected decrease by as much as -0.38 with substantial regional variations under the RCP8.5 CO2 emission scenario. Over this the century, it is anticipated that the seasonal amplitude of the H+ concentration will increase by as much as 80% under the same scenario.

Ocean Acidification Week 2021 was sponsored by the following organizations:

(1) GOA-ON, the Global Ocean Acidification Observing Network,

(2) NOAA, the United States National Oceanic & Atmospheric Administration,

(3) IAEA OA-ICC, the International Atomic Energy Agency – Ocean Acidification International Coordination Centre, and

(4) IOC-UNESCO – the Intergovernmental Oceanographic Commission of the United Nations Educational, Scientific and Cultural Organization

For more information, please visit

GOA-ON, YouTube, 24 September 2021. Text and video.

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