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Fact Brief - Is the ocean acidifying?

Posted on 8 June 2024 by SkS-Team

FactBriefSkeptical Science is partnering with Gigafact to produce fact briefs — bite-sized fact checks of trending claims. This fact brief was written by John Mason in collaboration with members from the Gigafact team. You can submit claims you think need checking via the tipline.

Is the ocean acidifying?

YesAcidification of oceans simply means a reduction in their pH outside of normal values.

The pH scale measures acidity and alkalinity of water-based solutions. It runs from 0 (highly acidic) through 7 (neutral) to 14 (highly alkaline). Any reduction in pH value, in the direction of 0, is acidification. The oceans acidify whenever they become less alkaline, regardless of whether their pH declines below 7.

A good analogy for acidification can be found with the way we talk about temperatures. If the pH of a solution shifts from 8.1 to 7.9, that is acidification, even though the solution remains slightly alkaline. In the same way, if the temperature rises from -40°C to -15°C, it has definitely warmed up, even though it's still freezing cold.

Since the Industrial Revolution, ocean pH has declined from 8.2 to 8.1 — a 30% increase in acidity.

Go to full rebuttal on Skeptical Science or to the fact brief on Gigafact

This fact brief is responsive to conversations such as this one.


Smithsonian Ocean Ocean Acidification

Encyclopædia Britannica PH | Definition, Uses, & Facts

National Oceanic and Atmospheric Administration What is Ocean Acidification?

European Environment Agency Ocean acidification

About fact briefs published on Gigafact

Fact briefs are short, credibly sourced summaries that offer “yes/no” answers in response to claims found online. They rely on publicly available, often primary source data and documents. Fact briefs are created by contributors to Gigafact — a nonprofit project looking to expand participation in fact-checking and protect the democratic process. See all of our published fact briefs here.

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Comments 1 to 4:

  1. "Since the Industrial Revolution, ocean pH has declined from 8.2 to 8.1 — a 30% increase in acidity."

    I'm not quite clear on the 30% increase in acidity." I understand how acidity increases as Ph drops. I don't know what to do with the numbers 8.2 to 8.1 in the context of a point 1 change creating a 30% acidity increase.
    Where do I go astray?
    Thanks to anyone who cares to help me out on this.

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  2. Eddie:

    Remember that pH is a logarithmic scale. This is explained in the links at the bottom of the post.

    To get actual concentration of H ions, you calculate 10-pH.

    • 10-8.1 = 7.943e-9
    • 10-8.2 = 6.31e-9

    Ratio between those two numbers is 1.26. So from that calculation, pH 8.1 is 26% higher H ion concentration than ph 8.2.

    If you want to calculate the other way, to see what pH is 30% higher than 8.2, we do 1.3* 6.31e-9 = 8.2e-9, and -log(8.2e-9 = 8.086.

    In round numbers, pH 8.1 is about 30% more acidic than pH 8.2. At a guess, the source of the original 30% figure is either rounding, or has slightly more precise measurements of the change in pH.

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  3. Both my wife and I thank you.

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  4. Eddie:

    Also keep in mind that the logarithmic/exponential nature of pH values means that any decrease of 0.1 in pH units means a 26% increase in acidity from the previous value - 8.2 to 8.1, 9.6 to 9.5, 10.9 to 10.8, etc. The ratio between the two numbers is always 10-0.1 = 1.26.

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