Ocean acidification is the change in the chemical composition of the ocean. When carbon dioxide (CO₂) is absorbed by seawater, chemical reactions that reduce seawater pH occur. A pH unit is a measure of acidity ranging from 0-14. The lower the value the higher the acidity of the environment. A shift in pH to a lower value reflects an increase in acidity. Sea water absorbs and dissolves 30 to 40 % of the CO₂ released by human activity. The change in the ocean’s chemical composition disrupts marine ecosystems and affects many creatures. The building of skeletons in marine creatures is particularly sensitive to acidity. For example, acidification dissolves and/or prevents the shells of some animals from forming.

Since the beginning of the industrial era, the ocean has absorbed some 525 billion tons of CO₂ from the atmosphere; presently around 22 million tons per day. Future predictions indicate that the oceans will continue to absorb CO₂, further increasing ocean acidity. Estimates of future CO₂ levels indicate that by the end of this century the surface waters of the ocean could have acidity levels nearly 150 % higher, resulting in a pH that the oceans haven’t experienced for more than 20 million years.

Some organisms will survive or even thrive under the more acidic conditions while others will struggle to adapt, and may even go extinct. Beyond lost biodiversity, acidification will affect fisheries and aquaculture, threatening food security for millions of people, as well as tourism and other sea-related economies.

Sources

https://ocean.si.edu/ocean-life/invertebrates/ocean-acidification
https://www.pmel.noaa.gov/co2/story/What+is+Ocean+Acidification%3F
https://www.nationalgeographic.com/environment/oceans/critical-issues-ocean-acidification/