Header graphic for print
Science, Law & the Environment Emerging Topics in Environmental Law

Ocean Acidification and Science Communication: The Seattle Time’s “Sea Change” Series and Cliff Mass’s Critique

Posted in Climate Change, Emerging Policy, Geeky Science Stuff, Ocean Acidification, Shellfish Industry, Water Quality

If you follow the Seattle Times, or ocean acidification as an emerging issue, you’ve likely seen Craig Welch’s “Sea Change” series published last month, a series that is impressive in terms of scope and depth of coverage of the issue of ocean acidification, with its possible impacts on marine life and our economy. I’ve been following how this series of articles has been reverberating around the internet and among thought leaders, and had a draft post put together on its distribution through syndicated media, how it passed through twitter, and how it may be influencing policy and science. I couldn’t get the post “just right” and it remains in draft form–and I’m somewhat glad it did because it delayed things until Cliff Mass posted a rather scathing critique of the Seattle Times on his blog this past Wednesday.

Cliff Mass’s critique raises some interesting points, and highlights the difficulties of communicating complex science through articles like what Craig Welch put together. If you have interest, I’d highly recommending reading both authors’ works. In short, Craig Welch and his team spent the better part of a year traveling and researching the impacts of increased atmospheric carbon dioxide concentrations on sea life–the premise being that increased carbon dioxide concentrations in the atmosphere drive the pH of ocean waters down, due to gas exchange with surface waters and the formation of a carbonic acid as a result. That acidification may result in impacts to sea life, and Craig Welch and his team wanted to document and highlight those potential impacts. One of his articles details the problems oyster growers here in the Pacific Northwest have had with failure of spawning events due to–as Craig Welch puts it–decreased pH of the waters those oysters are spawning in. He even goes on to characterize those waters as “corrosive” with the idea behind that label being the decreased ability of oysters to build calcium carbonate shells in such waters.

Cliff Mass jumped all over the Seattle Times in his critique, arguing that there is no demonstrated connection between atmospheric CO2, decreased ocean pH, and the problems the oyster industry is facing. He put together a series of data plots that show the decrease in ocean pH attributed to increased carbon dioxide emissions is about 0.1, while the natural variability of pH in coastal waters in the Northwest is much greater than that decrease, ranging from 0.6 to 1 pH units. He argues that this natural variability — being much greater than the decrease in pH due to increased carbon dioxide in the atmosphere — essentially dwarfs the pH decrease due to carbon dioxide in the atmosphere and therefore “it seems highly unlikely that changes in atmospheric CO2 are driving the large observed changes of ph (sic) of our local waters,” and as a result, atmospheric CO2 increases do not explain the problems being faced by the oyster industry.

So, who has it right? Craig Welch and the Seattle Times, or Cliff Mass?

The answer is neither party. Craig Welch–most likely because he was trying to translate complex science and chemistry into a form that was understandable to the public–used pH as a proxy for the real driver of the recent failures of oyster spawning events in the Pacific Northwest [EDIT Craig Welch rightly points out that he covers the issue of aragonite saturation in the oyster piece here, and in a previous article here]. Cliff Mass–most likely because he is an atmospheric scientist and not an aquatic chemist–missed diving into the detailed relationship between pH and the driver of the recent failures of oyster spawning events in the Pacific Northwest.

What is that driver? Well, the work of George Waldbusser et al. strongly suggests the important driver in terms of water chemistry isn’t pH but aragonite saturation state–a measure of the thermodynamic ability to form aragonite (a form of calcium carbonate present in oyster shells) from seawater. Above a value of 1, formation of aragonite is favored; below 1, dissolution of aragonite is favored. Aragonite saturation state is defined by the relative presence of calcium ions and carbonate ions in seawater–the building blocks of calcium carbonate. Carbonate is a form of inorganic carbon, and inorganic carbon in seawater comes in various forms, one being carbonate (CO3), another being dissolved CO2, and another being bicarbonate (HCO3-). These forms of inorganic carbon cannot all be measured directly, so researchers rely on models that use measured parameters in seawater (temperature, salinity, dissolved CO2, pH, or alkalinity) to calculate the carbonate ion concentration in seawater and then they can calculate aragonite saturation state.

So, seawater pH in one sense can be seen as a rough proxy of aragonite saturation state, which is why I think Craig Welch and others use pH when talking about ocean acidification impacts on oysters. As noted above, seawater pH can be influenced by atmospheric CO2 concentrations. But, seawater pH is also influenced by other processes, such as photosynthesis and respiration involving organic carbon, which is the likely source of the larger pH variations Cliff Mass discusses in his blog post. This is why seawater pH is a rough proxy at best for aragonite saturation state. Therefore, to be precise, Craig Welch should be referencing aragonite saturation state, at least when talking about impacts to calcium carbonate forming organisms.

Head spinning? See why science communicators need to simplify things? I have a Ph.D. in aquatic chemistry (with knowledge atrophied by years of being a lawyer) and it took me a good hour to go back through all of the above and try and distill things down for you. I THINK I have it right–but the lawyer in me puts that caveat on things, and I welcome comments if I missed anything.

Now that we are done with the aragonite saturation state primer, we can get at Cliff Mass’s contention that the oyster failures that have been observed are NOT due to rising CO2 levels in the atmosphere:

Can we state with any degree of certainty that the oyster spawning failures are due to a decreased aragonite saturation state? The answer at this point–largely based on Waldbusser’s work and work at the Whiskey Creek hatchery in Oregon–seems to be yes, there is both laboratory research and field data that support that conclusion. Can we then go on to attribute the decreased aragonite saturation state to increased CO2 concentrations in the atmosphere? The answer there is yes as well, at least based on the recent work by Katherine Harris and others that looks at the complex interplay of upwelling, freshwater inputs, biological processes, and atmospheric gas exchange on aragonite saturation state. That work shows that surface aragonite saturation states in modern upwelled surface waters along the Oregon coast are lower (0.66 to 3.9) compared to pre-industrial rates (1.0 to 4.7), a drop attributed to increased carbon dioxide in the atmosphere and gas exchange with upwelled surface waters. That work goes into extreme detail trying to tease out the different drivers of aragonite saturation state. It is worth noting that gas exchange is only one of those drivers, but appears to be the factor driving the drop in aragonite saturation states from pre-industrial levels. As I note above, aragonite dissolution is favored for values below 1, and oysters appear to need values of ~1.7 or above to thrive–so the drop from pre-industrial levels may be significant in oyster survival.

So, can we state that increased CO2 concentrations in the atmosphere are the possible cause of the problems seen in the oyster industry? Yes, because atmospheric CO2 is impacting aragonite saturation state-but not because of drops in pH in surface waters. That is an over-simplification of the issue.

Putting all this together, and refereeing Cliff Mass and Craig Welch, I think Craig Welch oversimplified in a necessary manner to communicate complex science. Cliff Mass–not surprisingly–looked at the issue from an atmospheric perspective and missed this issue of aragonite saturation state, although to his credit, he was just looking at the question of whether pH changes due to increased carbon dioxide was driving the observed problems in oyster production.

Okay. I’m well beyond my word limit for a blog post. What are the impacts of this debate? Cliff Mass has provided fodder for people skeptical of climate change impacts, which I don’t think was his intention (he was driving at scientific integrity and communication in the media). If you look at comments on other media coverage on this issue, you can already see that the Cliff Mass critique is being used by others to discredit the connection between rising CO2 in the atmosphere and impacts to the shellfish industry. That is unfortunate, because, for the reasons I state above, I think we are seeing impacts that are directly attributable to rising CO2 in the atmosphere. The story just isn’t simple.

  • Bill Dewey

    I think you have done a great job explaining the shortcomings of both Craig and Cliff’s coverage on the subject Doug. Thanks for taking this on. Your Ph. D in aquatic chemistry is paying off!

    • DougSteding

      Thanks Bill. To be clear, I think Craig’s work is important, and comprehensive, and, at least from the oyster industry perspective, validated by experience, unfortunately. I hope that Cliff Mass’s post doesn’t take away from the dialogue around ocean acidification started over the past few years and gathered and presented by Craig Welch in a compelling fashion. This also isn’t meant to be a critique of either of them-both are writers I really respect. Rather, it is meant to highlight how complex these issues are, and how difficult they can be to communicate to the science-consuming public.

  • No hive for me!

    Bull crap! If pH is a proxy, it is for the dissolved CO2 in the water (little makes acid), which suffocated the oyster larvae. The problem for oyster farmers was solved by waiting until past midday to draw fresh water. That was after the algae had a chance to switch from making CO2 from the available oxygen, to oxygen from the CO2 through photosynthesis. No acid involved. No “aragonite.”

  • Cliff Mass

    I did not “miss” the issue of aragonite saturation…I kept to ph because the ST article was centered on it. And as you undoubtedly know from your background, there is a very close relationship between omega (aragonite) levels and ph–so this is really not much of an issue. And what worries me most of all, is your comment at the end about the use of conversations like mine and ST by skeptics and “those trying to discredit the connection between rising CO2 and impacts to the shellfish industry.” The only way the public can be properly informed and scientific knowledge advanced is by a vigorous public discussion and evaluation of the issues. Those trying to push political and other agendas win if scientists like myself are silenced because our views are not popular among some. As you say, the story is not simple and the Seattle Times has tried to portray the situation as simple, with CO2 increases being the dominant problem for the “industrial” oyster hatchery industry….cliff mass

    • DougSteding


      Thank you for chiming in here. I agree that there needs to be vigorous public discussion on these issues. The point I was trying to make with respect to your blog post is that if you define the question narrowly (i.e., pH and connections to impacts to the shellfish industry) you may skip over underlying science that does show a connection between rising CO2 concentrations and impacts to that industry. I get why you did that because you were responding to the ST focus on pH. I get why Craig Welch focused on pH–it is a concept that the general public can understand, and if he started with a summary of aragonite saturation state, he would lose his audience. You are a highly credible member of the scientific community, and one that I’ve always respected. I would have liked to have seen you move on after your pH discussion go into an analysis like the one above–or to get into some of the research going on in this area to tease things out a bit more. Hopefully this dialogue can continue in public and in a way that goes into all the science on this subject–that will be a benefit to those that look to people like Craig Welch and yourself to understand the science behind current issues.


  • Tommy Carrig

    I did Acid Rain research at East Stroudsburg U in Pennsylvania. There have been some changes for the good. The Asian Brown Cloud is a concern
    It starts East of India.
    I did a song/youtube from searching, Save the. There are definitely effects.