Ocean acidification

The current drumbeat is that (anthropogenic) CO2 has caused the oceans to be 30% more acidic.  Acid oceans certainly sound worse than just reporting the pH.Acids dissolve carbonates, so the shells of shell fish and corals are supposed to dissolve or not form in acidified oceans.  Some of the explanations I’ve read give a technical explanation of acids being protons (the hydrogen atom nucleus) or sometimes just H+.  And if water has H+ in it, it is acidic.  At least in some explanations.  Carbonated water is made by dissolving CO2 in water (under pressure) and it has a pH of 3, so dissolving CO2 in water can make it acidic. Hydrogen ion concentration and pH are certainly inseparable, but reporting one without the other doesn’t mean much.

The pH scale, developed in 1909  is a measure of the hydrogen ion activity.  It runs from 1 (0.1 molar H+) to 14 (0.1 molar OH-).  7 is neutral.  Above 7 is considered basic and below 7 is considered acidic.  Ocean pH’s are generally taken as 8.2-8.3, so where does this ocean acidification with 30% more acid come from?  The simple strong acid/strong base calculation is pH = -log[H+], where H+ is the molar hydrogen ion concentration.  (Yes, I know about H3O+).  So using this simple approach, any decrease of 0.155 pH units is a 30% increase in H+ or acidity.  So, a decrease from pH 14 to pH 13.845 is a 30% increase in the hydrogen ion concentration.  I’m not I’d call pH 13.8, which is so high that the hydroxyl ion interferes with the normal glass electrode, acidification. Ocean acidification appears to be a rounded number assuming a decrease from about 8.3 to about 8.15.  When we see the concerns about ocean acidification we rarely see actual pH values.  pH is a better indicator, but not nearly as sexy as a claim of 30% acidification.  (

pH and environmental  tolerance varies by species and location.  Making blanket statements about “acidification” doesn’t seem warranted. Chesapeake Bay oyster larvae are the most susceptible to pH.  The best range is 6.75-8.75, a 100 fold range in hydrogen ion. The pH tolerance range for blue crabs is 6-8. Below 6 is lethal. For lobsters, the low pH tolerance seems to be 7.4-7.85 in various reports. Corals are the poster children for ocean acidification.  “Modern” historical variation in coral reef pH seems to be between 7.8 and 8.2.  Looking at environmental tolerances, temperature, salinity, nutrient loading and other factors seem to be more important than pH. 

The 30% increase in acidity sounds good as a PR bit, but I’m not sure it really means much if the pH and the tolerance range of a specific species is not included. 




9 responses to “Ocean acidification

  1. new paper,
    New paper finds no effect of “acidification” on plankton from CO2 levels 8 times higher than today
    A paper published today in Biogeosciences finds that prior claims about the effects of ocean “acidification” on calcifying plankton are highly exaggerated because the artificial laboratory conditions utilized do not correctly simulate the effects in natural seawater. The authors find exposure of the plankton to “acidification” from elevated CO2 concentrations of up to 3247 ppm [over 8 times higher than the present] had no effect on the life cycle (population density, growth and reproduction) of calcifying plankton when natural buffering sediment was present in the experiment.

    and this is worth a read which ties in with the above.
    from DR. JOHN T. EVERETT who worked for NOAA for 31 years,

    Statement of
    Joint Hearing on
    “EPA’s Role in Protecting Ocean Health”
    before the
    Subcommittees on Oversight and on Water and Wildlife of the
    Committee on Environment and Public Works


    Conclusion –

    “There is no reliable observational evidence of negative trends that can be traced definitively to lowered pH of the water. If there were, it would be suspect because there is insignificant change relative to past climates of the Earth. Scientific studies, and papers reviewing science studies, have similar messages. Papers that herald findings that show negative impacts need to be dismissed if they used acids rather than CO2 to reduce alkalinity, if they simulated CO2 values beyond triple those of today, while not reporting results at concentrations of half, present, double and triple, or as pointed out in several studies, they did not investigate adaptations over many generations. If there are reports of increases in ocean acidification in a region, the likely causes
    are upwelling, pollution, and rainfall (or runoff) and these all need to be addressed”

  2. It would be less annoying if it was just a PR bit. The public perception of science has never been informed by science; I take that for granted. What drives me mad to hear speeches about ocean acidification by the members of my own Zoology department and other university folk. I can’t believe they don’t know what they are talking about. If it’s not ignorance, it must be corruption, and I can’t stand the thought of my own university having become a dedicated provider of one or the other.

  3. They lie even when they are telling the truth. It is a lie by omission of material context. They are depending upon the ignorance of their audience to facilitate acceptance of their lies as truth. Then, if they are caught, they will claim they told the truth. Yet is something the truth if it is stated in such a way that it is almost certain to be misunderstood and when the speaker intends to take advantage of that misunderstanding? It is not!

    Such a statement infrequently made might well be merely sloppy and inattentive to detail. Yet, when many such statements on various topics are given repeatedly over a long period of time, even after being challenged, a willful intent to defraud is clearly evident. That it is given by a self identified expert in the field and sanctioned by and paid for by Government makes it far worse than simple fraud.

    Consider that the oath in court is “The WHOLE TRUTH and nothing but the TRUTH.” When under such an oath, if some material facts are left out of the statement given, a charge of withholding evidence and being in contempt of court can be handed down with substantial punishment given for the violation of the oath. Perhaps such an incomplete statement is not technically perjury but it is all but indistinguishable from it. Especially when there is a clear intent to deceive.

    The statement “30% more acidic” cannot be interpreted any other way than a clear attempt to deceive. Especially in context of your exposition of high school chemistry level information about PH. At the very least, the speaker of such lies has no moral right to claim the title of “scientist” or “authority on the subject”.

  4. Has anyone determined how the ppm increases in atmospheric CO2 would relate to changes in pH as an exercise in Henry’s Law. The real world would be complicated because of agitation in the ocean, thermal variations, currents, CO2 reactions with minerals, plants and microorganisms and other reactions. Nevertheless, it would seem the idea of significant changes in ocean pH is something that could be easily refuted by calculations.

    • I suppose you can make a simplified physical model of the ocean (or some part of it) that is simple enough to calculate, but it is not possible to calculate (or even estimate) anything if you’ve got life in that model.

      To get a feel of how pCO2 relates to pH in a live freshwater lake, have a look at this experiment:


      It is a simplified model, too, but close enough. BG-11 liquid medium, stationary Cynechocystis culture at 10e5 cells / cm3, fast alternating illumination (1h light / 1h dark). In the end, cells die after Rifampicin treatment on 07/10.

      All natural media are buffered (including rainwater); some are actively so (there is no water without life), so the question about the relationship between pCO2 and pH “in water” is ill-posed. In what kind of water?

  5. It is noteworthy that, in spite of all the CO2 that is claimed to be ‘acidifying’ the oceans, the concentration of alkali (as OH-) at a pH of 8.2 is about 250 times that of the acidity (as H+).

  6. Geologist Down The Pub Sez

    Instead of puzzling over moving the pH by 0.1 or so, why not look at the physical record left from when there was a lot more CO2 in the atmosphere (and by logical extension in the oceans, as well). What conditions then prevailed?

    Well, take a look at the Cretaceous sediments, or the early Cenozoic sediments of the Florida peninsula: We have thick (+ 2 kilometers) of calcium carbonate deposited by plankton which secreted internal calcite skeletons. When the plankton died, their tiny internal skeletons settled slowly (I mean slowly – Stokes Law and all that) to the bottom a couple of hundred feet below, through all that supposedly “acid” ocean water. A low pH, below 7.0, would dissolve them in a few inches of settling.

    Always look to geology when your time-frame is too long for direct observation to determine the outcome of an experiment.

  7. Worthwhile facts. Fortuitous everyone I ran across your internet-site by accident, that i’m amazed the reason this particular accident could not occurred sooner! I book-marked them.

  8. Human CO2 emissions annually only contribute [carbonic] acid 1 part per 50,000,000,000 annually — 1 to 50B, annually. BFD. Why hasn’t someone made this point?

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s