A plea to ocean acidification scientists

It is unfortunate that the terminology used in some papers, presentations and media interviews is misleading. The definition of “acidic” in the Oxford English dictionary is “having the properties of an acid; having a pH of less than 7”. Despite the process of ocean acidification (the acidity of seawater, or hydrogen ion concentration, has increased by 28% since preindustrial time), the oceans are alkaline (pH higher than 7) and will not become acidic in the foreseeable future in most regions of the oceans. Hence, while it is accurate to refer to an “increase in acidity” or to “ocean acidification”, the terms “acid” or “acidic” should not be used when referring to seawater. Note that there are few exceptions, seawater can be acidic in some near-shore environments such as estuaries, in the immediate vicinity of CO2 vents, or in purposeful perturbation experiments.

The importance of using accurate terms cannot be underestimated. Our community does not want to be seen as using improper terms, especially considering the intense scrutiny by the media and general public ahead of COP21.

Some of us have made this mistake in the past but let us ban the future use of “acid” or “acidic” in the context of our work.

Members of the SOLAS-IMBER Working Group on Ocean Acidification:

Jean-Pierre Gattuso, Jim Barry, Jelle Bijma, Sarah Cooley, Minhan Dai, Richard Feely, Dan Laffoley, Nelson Lagos, Richard Matear, James Orr, Ulf Riebesell, Lisa Robbins, Carol Turley, Patrizia Ziveri

9 Responses to “A plea to ocean acidification scientists”

  1. 1 agdickson 26 August 2015 at 18:13

    Although I am in broad agreement with the sentiment expressed here, I am not happy with the initial rationalization. Certainly the OED does document our usual usage of the process “acidification” with a 2006 quotation; but the choice of pH 7 as a line in the sand between acid and base is a gross oversimplification (OK for pure water at 25 °C, but for little else).

    On a related note, the OED defines “alkalinity” as the “quality or state of being alkaline”, a far cry from the the use of the term in marine science; hence my preference for the expression “total alkalinity”. (The older term “titratable base” is, perhaps, clearer.) However, “alkalinity” is commonly used to mean “titratable base” in technical literature, if not by the OED (e.g., Wikipedia). In fact, I think the discussion hinges on the confusion between the concept of a “neutral” solution (one that is neither acidic nor basic, i.e. [H] = [OH], — which really only has much meaning for strong acid / strong base mixtures, and the more elaborate concepts of “acidity” and ”alkalinity” that are used in the water industry and in geochemistry when discussing solutions containing a variety of weak acids and/or weak bases.

    So, I suspect that this plea (though defensive and well-meaning) may verge upon on the “foolish consistency” that Emerson cautioned us against. :-)

  2. 2 Jean-Pierre Gattuso 27 August 2015 at 09:53


    On your first point, I am glad that you agree with the plea to refrain from using the terms “acid” or “acidic” when reporting on anthropogenic ocean acidification. The definition used in dictionaries is an oversimplification but it is the one used by everyone, except the few scientists familiar with the intricacies of the carbonate chemistry. The point is that our community is interacting with policymakers as well as the general public and must use a language they understand.

    I fully agree with your second point. Lay-people are very much confused when it comes to “alkalinity” but that is a distinct from our plea.

    Thanks for commenting! I invite others to chime in too.


  3. 3 agdickson 27 August 2015 at 10:31


    I wasn’t clear enough; my real point is that it is difficult (if not impossible) to write about acid-base chemistry in clear and non-technical language in a way that remains consistent and correct. It is a worthy aim, but one that is easier to criticize than to achieve.


  4. 4 Tom Trull 27 August 2015 at 22:40

    I don’t think the guidance is helpful. The ocean is more acidic than it was a century ago, and more (weak) acid is now in the ocean than before. So the terms acidic and acid can be useful and correct. The problem comes in only when the terms are incorrectly used as describing the ocean state relative to the commonly used freshwater acidic/basic divide of pH 7. So, rather than banning useful terms, the guidance would be more helpful if it simply reminded the community of their correct usage. (We certainly don’t want editors globally removing these words from texts under some misconception that they are inappropriate in all contexts!).

    More generally, as pointed towards in the very useful comment from Andrew Dickson, it’s perhaps time that the chemical oceanography community defined an acid/base neutral point more meaningful than pH=7, and gave it a new name. The Holocene pre-industrial mean pH of seawater is one option, an equivalence point for an abundant acid-base pair is another (HCO3-/CO32-). Finding the best choice (if there is such a thing) would no doubt require another working group and some years!

    In the meantime, yes, let’s be careful with our language, but without descending into the picayune.

  5. 5 terryjohnson2014 28 August 2015 at 20:21

    I’m not a scientist but work in extension; I try to interpret for the public the results of the work you scientists do, and I have felt from the beginning that “acidification” is an unfortunate choice of words, and “acidic water” even more so. Irrespective of what those terms mean to organic chemists, they do not accurately communicate to the layman what is happening in the oceans. To the public those loaded words suggest that the sea will soon dissolve the metal in their boats or even burn their skin.Since that isn’t happening, the situation adds credence to those who sow doubt about the field of climate science. It is important for scientists to remember that the public pays the bills and their work should be accessible and understandable to the public. Science is better served when scientists communicate more clearly with their employers–the public–using the common meanings of words where possible. “Ocean neutralization”, “ocean decalcification”, “diminished alkalinity”? I don’t know, you guys are the technical experts, but this is a plea for you to think about the common as well as technical meaning of the words you use.

  6. 6 kencaldeira 28 August 2015 at 21:14

    The Arctic is cold. It will remain cold even with global warming.

    However, it makes sense to talk about the warming of the Arctic despite its being cold. It also makes sense to talk about the Arctic being warmer than it was a century ago even though it is still cold. One might also say that the Arctic is ‘warm’ relative to what it was a century ago.

    It is not making a mistake to use the word ‘warm’ or ‘warmer’ in this context. In these contexts, ‘warm’, ‘warming’ and ‘warmer’ refer to signs of change and not absolute values.


    Carbon dioxide in the ocean acts as a weak acid, in that it donates protons to solution.

    The addition of a weak acid into the ocean is making the ocean more acidic, in that it is decreasing the pH of the ocean and bringing it closer to the acid end of the scale.


    It is as if I were to declare that I am not going to call anything ‘warm’ unless the temperature is greater than 25 C, and then you claim that nobody can talk about the warming of the Arctic until the temperature reaches 25 C.

    This is an absurd position.

    It makes sense to use terms like ‘acid’, ‘acidic’ and ‘acidification’ in reference to directions of change and in comparative contexts (c.f., the Arctic is warmer than it was a century ago; the ocean is more acidic than it was a century ago.) These statements do not mean that the Arctic is warm or the oceans are acid in any absolute sense; they are relative statements.

    In this context, ‘warmer’ means ‘higher temperatures’ and ‘more acidic’ means lower pH.

    This has been standard usage in the discussion of ocean acidification for over a decade. It is not helpful to try to change this usage at this time.

    The post ends:

    “Some of us have made this mistake in the past but let us ban the future use of “acid” or “acidic” in the context of our work.”

    Better would have been,

    “With regard to ocean acidification, let us reserve the use of terms such as ‘acid’ and ‘acidic’ to contexts where comparisons are being made or reference is being made to a sign of change; in most oceanographic contexts, it is is incorrect to use these terms to describe seawater in an absolute sense.”

    • 7 Jean-Pierre Gattuso 23 November 2015 at 07:11

      The expression “ocean acidification” is perfectly fine as it describes a change in pH towards the acidic end of the pH scale. The comparison with the process of warming used by Ken Caldeira is correct. Actually, several of us were coauthors of FAQs that used this comparison to justify the use of the expression “ocean acidification”.

      Ken’s other points are addressed in our generic reply to other comments.

      Members of the SOLAS-IMBER Working Group on Ocean Acidification:

      Jean-Pierre Gattuso, Jim Barry, Jelle Bijma, Sarah Cooley, Minhan Dai, Richard Feely, Dan Laffoley, Nelson Lagos, Richard Matear, James Orr, Ulf Riebesell, Lisa Robbins, Carol Turley, Patrizia Ziveri

  7. 8 M Riza Iskandar 28 August 2015 at 23:47


    I agree with your explanation, the terms of ‘acid’ or ‘acidic’ in the ocean is reffered the pH become lower than normal pH of the ocean (anomaly pH). The terms is something similiar with anomaly SST, when el-nino occur.

  8. 9 Jean-Pierre Gattuso 23 November 2015 at 07:12

    We are grateful for the many comments and would like to refine our original plea. The final sentence of our plea suggested banning the terms ‘acid’ and ‘acidic’ when referring to seawater, but it was too short to reflect our earlier qualifications referring to relative changes. It would have been more precise to suggest that we avoid using ‘acid ocean’, ‘acid seawater’, ‘acidic ocean’, and ‘acidic seawater’, when used in an absolute sense. Relative terms such as ‘more acidic seawater’ can be used but are prone to confusion unless it is also made clear that ‘more acidic’ does not mean that seawater is actually ‘acidic’. Unfortunately, such nuances are often lost when communicating with journalists, policymakers, or other non-scientists and can fuel unfair criticism from deniers. So let us strive for extra clarity when dealing with those outside our discipline.

    Members of the SOLAS-IMBER Working Group on Ocean Acidification:

    Jean-Pierre Gattuso, Jim Barry, Jelle Bijma, Sarah Cooley, Minhan Dai, Richard Feely, Dan Laffoley, Nelson Lagos, Richard Matear, James Orr, Ulf Riebesell, Lisa Robbins, Carol Turley, Patrizia Ziveri

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