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Fact Brief - Is the ocean acidifying?
Posted on 8 June 2024 by SkS-Team
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Is the ocean acidifying?
Acidification 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.
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Sources
Smithsonian Ocean Ocean Acidification
Encyclopædia Britannica PH | Definition, Uses, & Facts
National Oceanic and Atmospheric Administration What is Ocean Acidification?
European Environment Agency Ocean acidification
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"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.
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.
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.
Both my wife and I thank you.
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.