The Curry test for ocean acidification

There’s a recent post about ocean acidification on Judith Curry’s blog, Climate Etc. She includes the commentary from two opposing views on this topic and then weighs up the evidence herself and decides whose views she finds more credible.  The two points of view come from these two people:

* Scott C. Doney – senior scientist at the Woods Hole Oceanographic Institution. He has a Ph.D. in chemical oceanography and his research interests are marine biogeochemistry, ocean acidification, global carbon cycle, and climate change.

* Craig D. Idso – founder and chairman of the Center for the Study of Carbon Dioxide and Global Change. He has a Ph.D. in Geography and reportedly receives $11,600 per month from the Heartland Institute. The Heartland Institute is a right-wing think tank which no longer discloses its sources of funding but has previously received money from Exxon Mobil and in the 1990s worked for big tobacco to question the science linking smoking with cancer. He is not affiliated with any university and has not had anything published in a scientific journal that I could find.

I am quite surprised that for the contrary view, Curry has chosen Craig Idso who does not have a speciality in this area but who has a conflict of interest which she does not mention. For these reasons, I would give more weight to the views of Scott Doney. Craig Idso also uses some quite emotive language in his story like “extreme one-sided” and “propagandized view”.

Despite all of this, Judith Curry scores Idso’s story more highly than Doney’s. Her reason for doing so is because she says Doney’s testimony is normative. What does normative mean? It’s the apparent subtle inclusion of policy arguments when presenting scientific information through the use of value-laden words like “degradation”, “good” or “poor” . Curry concludes that Idso’s testimony is normative because she conducts a word search of his testimony and does not find many statements with the words “uncertain”, “disagreement”, “debate” or “unknown”. Here’s what she says:

I found Doney’s testimony to be highly normative, something that I am not a fan of in testimony by scientists.  I did a word search, looking for ‘uncertain’, ‘disagreement’, ‘debate’, ‘unknown’.  The only statements I found were:

She then copies and pastes two sentences that do include some of these words and goes on to say,

For these reasons, Doney’s testimony didn’t score too high on my credibility meter, in spite of my acknowledgement of his expertise and stature in the field.

Does this seem a little odd to anyone else? I think Judith Curry is trying to suggest that Doney’s research is driven by certain underlying assumptions and biases but I cannot see how the inclusion or exclusion of words like “uncertain” or “disagreement” is evidence of this. My conclusion is that if an expert in the field of ocean acidification is describing current knowledge without littering their description with the words “uncertain” or “disagreement” then this is probably a reflection of the level of scientific consensus in this area rather than a covert attempt to sway public policy.

I acknowledge that I am probably biased – I am not a fan of the heat and I love coral reefs and I have unwavering respect for science – so I am going to paste some of Scott Doney’s testimony to the Committee on Environment and Public Works here below and completely ignore the views of Craig Idso. If anyone wants to see whether there is a contrary view and what it is, I would recommend going to your local library (a method for research I learnt in primary school) and search the peer-reviewed literature for “ocean acidification” and “coral” or “marine organisms” or something similar. This is what I have done and there is more support for Doney’s views than for Idso’s in my humble opinion.


The ocean uptake of excess atmospheric carbon dioxide, the excess above preindustrial levels driven by human emissions, causes well-understood and substantial changes in seawater chemistry that can affect marine organisms and ecosystems(Doney et al., 2009; Gattuso & Hansson, 2011). Carbon dioxide (CO2) acts as a weak acid when added to seawater leading to the release of hydrogen ions (H+) and bicarbonate (HCO3) ions:

CO2 + H2O => H+ + HCO3

The reaction increases seawater acidity and increases the hydrogen ion activity, thus lowering seawater pH. pH is defined as the negative logarithm of the hydrogen ion activity, so that a 1-unit change in pH is equivalent to a 10-fold change in H+. Most of the extra hydrogen ions react with carbonate ions (CO32-) and lower their ambient concentrations:
H+ + CO32- => HCO3

This second reaction is important because reduced seawater carbonate ion concentrations decrease the saturation levels of calcium carbonate (CaCO3), a hard mineral used by many marine microbes, plants and animals to form shells and skeletons. Many organisms require supersaturated conditions to form sufficient calcium carbonate shells or skeletons, and biological calcification rates tend to decrease in response to lower carbonate ion concentrations, even when the ambient seawater is still supersaturated.

I think it’s also worth mentioning that the coral reefs have disappeared in the past. According to reef ecologist, Peter Sale, the world’s coral reefs completely disappeared in each of the previous five mass extinctions and they were gone for tens of millions of years at a time.

A different article from the journal Nature from 2011, Earth’s Acid Test, has something similar to say:

Some 55 million years ago, during an episode of extreme global warming driven by a spike in atmospheric CO2, the pH of sea water is thought to have dropped to levels similar to those expected at the end of the twenty-first century. Ocean sediment deposited during that period contains very little carbonate and no fossils of microorganisms with calcium carbonate shells, indicating that the sea water became too corrosive for calcifying algae such as deep-sea foraminifera, driving many to extinction. Today, acidification is progressing at least ten times faster than it did 55 million years ago.

Below is a graph from the same paper which shows how rising carbon dioxide and ocean pH will affect different organisms at different times. The coloured lines represent four different carbon emissions scenarios. Click to enlarge.


11 thoughts on “The Curry test for ocean acidification

  1. Rachel…there’s an evidential elephant in the room, and that is the role of overfishing. A number of studies have concluded that fish are responsible for a high proportion of the calcium carbonate in the oceans, thus maintaining alkalinity levels. Over the past century however we have overfished like crazy, and it is simply an exercise in logical deduction to realise that a big reduction in fish stocks will cause reduced alkalinity (colloquially referred to as ‘ocean acidification’).

    So yes, so-called ocean acidification may be anthropogenic, but not primarily because of CO2.


  2. Let’s see…

    A policy goon from the oil funded Heartland Institute faces off with an actual scientist on the issue of ocean acidification and spouts off a bunch of nonsense. Then a reporter, who knows nothing about the science, uses the verbal judo term ‘normative’ in an attempt to undermine the scientist’s authority.

    First, the scientist is the only real expert in the room. Second, the Heartland guy has a clear conflict of interest. Third, the reporter apparently engages in journalistic hackery and subtle ad-hominem against the scientist.

    For my part, I would ditch any statement from either the journalist or the oil company shill as irrelevant. Since there is only one scientist in the room, there is no debate, just some valid information put out by one expert and then a bunch of nonsense put out by two clowns.

    I’m sorry you experienced such a dishonest travesty.

    1. PS

      The article posted by the above commenter is rank misinformation. Ocean acidification is a clear response to high CO2 levels. There’s an easy test for this that any oceanographer knows — pump more CO2 into a volume of water and the acidity goes up.

      Once again, climate change deniers are trying to confuse basic physics…

      Here’s the basics about ocean acidification from the climate scientists at NOAA. I don’t know about you, but I’ll stick with NOAA over Heartland oil shills, snarky journalists, or denialist articles from queastionable sources any day of the week.

  3. Scribbler…Judith Curry is a climate scientist, not a journalist. It always helps if warmists accusing others of dishonesty can get their basic facts right themselves.

    1. > It always helps if warmists accusing others of dishonesty can get their basic facts right themselves.

      Sure. It always helps warmists, for contrarians can make any kind of accusations without needing to get their facts straight. A relevant example is this:

      [Talking about acidification] makes people believe oceans are turning into skin-dissolving soups.

      When confronted with the fact that lake water could naturally be acid, what do we read?



      Another example is that other contrarian commenter that revisit the archeology of the concept of “acidification”:

      First use of “acidification” as opposed to reduced alkalinity, appears to be in 1 2003 article by Ken Caldera.

      This conjecture is only off by at least 45 years or so:


      In that thread, all that remains are what contrarians do best:

      One can only speculate.

      This, of course, does not prevent anyone to investigate. In fact, to investigate and to speculate go hand in hand.

      The truth is out there.


      BTW, does the term “warmist” apply to those who are for warming?

  4. Robert…you clearly don’t understand the science, or the papers cited in the article I linked to above. The pH level of the oceans is significantly determined by fish, not CO2. Take away the fish, as we have been doing, and the trend will be to a slightly less alkaline ocean, as we have been seeing. If you cannot follow that from the research then you need to do a refresher course.

    In the oceans there is huge variability in pH levels, and life not only thrives in all areas, but moves about frequently between areas with a higher vs lower pH. The ocean acidification scare is a non starter. Sorry to burst the bubble.

      1. Hi Rachel, yes I’m quite comfortable with the chemistry that rising CO2 lowers the pH of water, the issue is to what degree this occurs in an open system. An ocean is not an enclosed lab experiment, and the fact that fish play a huge role in keeping the oceans alkaline is an example of real life interfering with an otherwise perfectly good science experiment. The links to the research on fish are in the article I linked above, but there’s some other useful material cited in the Curry thread.

        I’m of the view that anthropogenic deforestation over the past 200 years is responsible in part for the growing ratio of CO2 in the air – Earth’s lungs having been cut in half. Therefore I wasn’t surprised at the implications arising from that other great human pastime, overfishing.

    1. “The pH level of the oceans is significantly determined by fish, not CO2. Take away the fish, as we have been doing, and the trend will be to a slightly less alkaline ocean, as we have been seeing.”

      Even if fish account for 15% of the carbonate in sea water, soluble carbonates entering from rivers or dissolved from limestone sea shores account for the other 85% (or is it even as much as 95%?)

      The rate of ocean acidification cannot be accounted for by reduction in the fish population.

      It is true that deforestation is a significant contributor to the atmosphere’s CO2 load, but it is a mistake to assume that reducing fish population has a similar effect. What is missing is evidence. Over-fishing may be making the problem slightly worse, but the main correlation of ocean acidification is with CO2 concentration in the atmosphere.

  5. The paper that Ian cites has appeared in a reputable scientific journal and deserves to be taken seriously. Therefore I checked it in Google Scholar. The actual citation is “Contribution of Fish to the Marine Inorganic Carbon” DOI: 10.1126/science.1157972, 359 (2009); 323Science

    However it is well known that serious papers may have their conclusions reinterpreted, modified and even contradicted by subsequent research. So I looked at the citations, of which there are 80 – a number that indicates that other scientists have given some consideration to this work.

    One of the earliest is “Impacts of Climate Change on Marine Organisms and Ecosystems”, Andrew S. Brierley, Michael J. Kingsford,

    They explore the relationship between atmospheric CO2 concentration and ocean acidification, noting:

    “There is a direct relationship between CO2[atm] and ocean pH as CO2[atm] increases, pH drops. This poses a great threat to many marine organisms and ecosystems. Over the past 200 years, the oceans have absorbed approximately half of the anthropogenically-generated CO2[atm] and at present a further approximately 1 million tonnes of CO2 diffuse in to the world ocean per hour. The rate of decreasing pH, 0.1 units in the last 200 years and an expected drop of 0.3 to 0.5 units by 2100, is more than 100 times as rapid as at any time over the past hundreds of millennia”

    They go on to note that;

    “At present, shallow waters are generally saturated with carbonate ions, but dissolution increases with depth. The lysocline — the depth at which dissolution begins — will shallow as oceans become more acidic, reducing the depth range that offers suitable habitat for calcifying organisms. Even for shallow waters, a CO2[atm] greater than c. 490 ppm will compromise the capabilities of corals to make strong skeletons and loss of coral reefs will ensue The direction of change in calcification that acidification will bring is, however, questionable: studies of the coccolithophore Emiliania huxleyi suggest both thickening and wasting of calcareous shells, and excretion of precipitated carbonates by teleost fish is predicted to rise with ambient CO2. There is, thus, an urgent requirement for improved understanding of the effects of acidification from the cellular to ecosystem level.”

    Clearly the mitigating effect that fish have on ocean acidification diminished by reduction in global fish stocks is a factor to be considered, but it is simplistic to claim that “a big reduction in fish stocks will cause reduced alkalinity (colloquially referred to as ‘ocean acidification’)”, and that that is the primary cause of ocean acidification.

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