Climate at a Glance: Ocean Acidification

Thriving marine life on a coral reef -licensed from 123rf

View this page in our printable booklet (PDF) here:

Key Takeaways:

  • Ocean water is not overly acidic.
  • A pH of 7 is considered neutral. A pH below 7 is acidic. A pH above 7 is alkaline.
  • The pH of the oceans averages 8.1, and it ranges from 7.8 to 8.5. By comparison, rainwater is “acidic,” averaging 5.6.
  • Since 1850, the pH of surface ocean waters has fallen by merely 0.1 pH units.
  • The health of ocean life is improved, not harmed, by more carbon dioxide (CO2). CO2 is food for phytoplankton that form the foundation of the marine food chain. Marine life thrives and improves growth rates in elevated CO2 conditions.

Short Summary:

Scientists and media outlets claim ocean acidification is occurring due to increased carbon dioxide (CO2) levels in the atmosphere,1 but objective data show the oceans are far from acidic.

A pH of 7 is considered neutral, with anything below 7 considered acidic. Ocean pH averages 8.1, which is alkaline rather than acidic. Climate models suggest the ocean’s surface pH may have dropped from pH of 8.2 to 8.1 since 1750, though that change was never actually measured. In reality, the very small pH drop is merely a modeled conjecture.2

A study by scientists at the CO2 Coalition notes that the health of ocean life is enhanced by more carbon dioxide, not less.3 CO2 is food for phytoplankton, which form the foundation of the marine food chain.

As Figure 1 shows, with an average pH of 8.1, the oceans are a long way from turning acidic. It is likely that
media reports often use the word “acidic” because it sounds scarier than a more accurate description, such as “a modeled, modest decline in alkalinity.”

Figure 1: Comparison of the pH of common substances.
Data source: U.S. Environmental Protection AgencFigure 1. Comparison of the pH of common substances. Source: U.S. Environmental Protection
Agency, “Measuring Acid Rain,”, last accessed August 12, 2021,


  1. Pacific Marine Environmental Laboratory, “What is Ocean Acidification?,” National
    Oceanic and Atmospheric Administration, accessed August 12, 2021, https://www.
  2. K. Caldeira and M.E. Wickett, “Ocean Model Predictions of Chemistry Changes from
    Carbon Dioxide Emissions to the Atmosphere and Ocean,” Journal of Geophysical
    Research, Volume 110, September 21, 2005, https://agupubs.onlinelibrary.wiley.
  3. CO2 Coalition, Ocean Health: Is There an ‘Acidification’ Problem?, June 2020, accessed
    August 12, 2021,

Climate At A Glance is a Project of The Heartland Institute