The Oceans are Not More Acidic Now Than in the Past 300 Million Years [UPDATED]

…despite what the Guardian says. Update: …as the Guardian now agrees.

[Update: 9 Oct 2013 13.01 pm: The headline and first paragraph of the article have now been changed following email correspondence between Fiona Harvey and me. Credit to Fiona and the Guardian for this response. The links now lead to the updated version which can be compared with the screenshot below. Further update: See also http://www.newssniffer.co.uk/articles/690315/diff/0/1 for a side-by-side comparison.]

Fiona Harvey’s article in the Guardian on 3 October 2013 Ocean acidification due to carbon emissions is at highest for 300m years misrepresents the scientific literature. This error has propagated across the Twittersphere.

(H/T Latimer Alder for the tweet that alerted me to this article)

Harvey wrote (my emphasis)

‘The oceans are more acidic now than they have been for at least 300m years, due to carbon dioxide emissions from burning fossil fuels, and a mass extinction of key species may already be almost inevitable as a result, leading marine scientists warned on Thursday.

In the starkest warning yet of the threat to ocean health, the International Programme on the State of the Ocean (IPSO) said: “This [acidification] is unprecedented in the Earth’s known history. We are entering an unknown territory of marine ecosystem change, and exposing organisms to intolerable evolutionary pressure. The next mass extinction may have already begun.” It published its findings in the State of the Oceans report, collated every two years from global monitoring and other research studies.’


Harvey 2013 article screencap

Harvey’s phrase ‘oceans are more acidic now than they have been for at least 300m [million] years’ was tweeted (paraphrased) by a number of accounts including

naturegeoscience tweet
[@NatureGeosci original tweet deleted][Update: see @NatureGeosci response below]

Update: see corrected Newshour article.

and questioned by a few



[Update (9.10.2013): and by Paul_K and others in the comments in the Guardian article, see my comment below]

What does the State of the Oceans Report actually say?

Harvey’s article does not give an exact source for her assertion, and there does not seem to be a single ‘State of the Ocean Report‘ but a series of papers in a special issue of Marine Pollution Bulletin (open access).

In one of the linked articles, (Bijma et al. 2013, Climate change and the oceans – What does the future hold? (Marine Pollution Bulletin 2013, in press)) the authors say

‘the present day carbon perturbation and the concurrent ocean acidification is unprecedented in the Earth’s history and occurring much faster than at any time in the past 55 million years (Kump et al., 2009) or even 300 million years (Hönisch et al., 2012; Fig. 5).

The term ‘acidification’ as used here is ambiguous, but from their cited references it appears that Bijma et al. mean the rate of acidification rather than the extent of acidification (level of acidity) of the oceans. In fact the references make clear that the oceans are currently more alkaline than in almost all of the past 300 million years.

Bijma et al. cite Hönisch et al. 2012, The geological record of ocean acidification. Science 335, 1058 (paywalled). Figure 4D of Hönisch et al. shows the pH of the ocean over the past 300 million years (low pH = high acidity).

Figure 4D from Hoenisch et al. 2012

Figure 4D from Hönisch et al. 2012 (click on image to expand)

The whole of Figure 4 is shown here.

Bijma et al. 2013 also cite Kump, L., Bralower, T., Ridgwell, A., 2009. Ocean acidification in deep time. Oceanography 22, 94–107 which shows a similar graph in Figure 1B, which is not surprising since Ridgwell was the author of reference 73 in Hönisch et al. 2012, and so appears to be the ultimate source of both graphs.

Pearson and Palmer 2000 (Atmospheric carbon dioxide concentrations over the past
60 million years
Nature 406: 695-699 – open access) was not cited by Bijma et al. 2013, but also showed that ocean pH has been much lower (more acidic) than today during the past 60 million years as shown below.

Pearson and Palmer 2000 Figure 1

Pearson and Palmer, Nature 2000 Figure 1

My Conclusion

Hönisch et al. 2012, cited by the State of the Oceans report, showed in Figure 4D that the ocean has been more acidic for most of the past 300 million years than it is now. The rate of acidfication may be faster now, but Hönisch’s graph has a resolution of 20 million years, so cannot address that question.

It is unfortunate that an environmental journalist should confuse the rate of acidification with levels of acidity, but appalling that this story was tweeted uncritically by Nature Geoscience and a number of climate scientists other influential accounts. This is not some esoteric area of climate science. It is well known that CO2 was much higher during parts of the past 300 million years than it is today and therefore ocean surface pH would be expected to be lower. Why was Harvey’s assertion that “[the] oceans are more acidic now than they have been for at least 300m years” not challenged (as far as I can see) by anyone from the scientific establishment?

I will email a link to this post to Fiona Harvey. The Guardian could of course respond by quietly changing the text of the first paragraph to say ‘The oceans are acidifying faster now than …’ but that will not recall the egregious tweets that have publicised a false picture of ocean pH by many who should know better. [Update: which is exactly what they did]

Update 7 Oct 2013: Kudos to Nature Geoscience for the following response

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34 thoughts on “The Oceans are Not More Acidic Now Than in the Past 300 Million Years [UPDATED]

    • My post isn’t about current changes, but for what it’s worth, I think that the evidence points towards a small acidification of the oceans as CO2 rises. See AR5 WG1 ch 3 (3.8.2) – observations date back only a few decades, but are in the direction of acidification.

      • Ruth — Scientifically, I think it is safe to say that for the small changes currently measured, the data set is way way to short to make any long term claims, about a chemical phenomena that is nearly always only significant on a local basis.

        Any statement about “Ocean pH” is fraught with the same dangers as as GMST. What exactly are we measuring?, where?, is a “global” value even meaningful, even if it could be determined physically?

        Like GMST, any data set about the past (more than 50 years, I would venture) are really guesses based on approximate measurement or proxies, with error ranges so broad as to be almost meaningless.

        I have lived on the sea, full time, for the last ten years — and spent another ten years at sea in my prime years. The is no one “ocean” pH, no one “ocean” surface temperature any more than there is one “ocean” weather. These are human constructs that have to relationship to the real world.

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  2. – Brilliant microcosm of the logic of the entire climate debate :
    Driven by fear : “what if”, “think of the children” the ‘true-believer’ side rush on on to conclusions and mock the uncool, unartistic, geeky ‘old’ skeptics and say “how can that ‘small group’ possibly be right and ‘us’ and the authoritive Guardian & BBC be wrong ?”

    – And we can trust the “consensus scientists” cos they stepped forward to correct the public record ? Oh seems like a “no”, cos after 4 days none have.

  3. Reblogged this on CraigM350 and commented:
    Sadly a reflection of journalism by press release, compounded by retweeting. Kudos to Nature Geoscience for correcting, wouldn’t expect the Guardian to follow suit.
    Thank you. 🙂

  4. Well done on doing what the journalists should have tried to do and the scientific community absolutely should have done. The authors of the paper must have alerted the Guardian they’d seen the article because it was temporarily withdrawn for publishing before the end of the time embargo. They should have corrected the flawed impression of the science at the time.

    I’ll admit I didn’t give the claim much of a thought but did wonder how long it would take to turn out to be rubbish. 4 days would have to be a record!

    I will take pleasure in drop kicking this claim every time it’s directed at skeptics, which will be regularly because the corrections rarely get much further than the sceptic community. Many thanks.

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  6. Seems to me that ocean acidification increasing more now than at any time in the last 55 million years is bad enough. Especially when you add overfishing, nutrient pollution etc.etc.

    • Short term changes and spikes cannot be determined and detected very far back. It might have swung up and down at 10x the present rate for all we can tell from the paleo record. The error band is about 20 million years; anything can happen and reverse in that time.

    • Alternatively, one could take the view that decreasing the Ocean’s alkalinity is simply helping the planet to revert to the pristine conditions of 300 million years ago. 🙂

    • All chemical substances have an “acidity” — the ocean’s acidity is increasing. (And all chemical substances have an “alkalinity.”) So “acidification” is indeed the correct term (and simplier than “dealkalination”).

      • ‘Neutralisation’ works just fine.

        Technically accurate and does not carry the emotive baggage of ‘acidification’. Uses only one more letter so no probs with word/letter count.

        Why not ‘neutralisation’, Mr Appell?

  7. The Guardian article was despicable alarmism. It would have the masses (and PPE-grad politicians) believe that any reduction in obesity is smoking gun evidence of increased anorexia.

    The warmies are struggling. Won’t be long now.

  8. David: We’ve been adding a ‘significant’ (according to AGW theory) carbon dioxide to the air for what, sixty years or so? Do you in you wildest imagination believe that we could determine either the date or duration of an event that happened a ten thousand years ago to be within a sixty year window (we can’t date the Shroud of Turin that closely, and we have the actual shroud! We must use proxies to date past ocean pH!) Yet you are willing to believe that we could measure the ocean acidification changes of a sixty year period anytime during the last 55 million years? Take a look at the graphs above. See all those sharp rises and drops? We have absolutely no way of determining if those changes took place overnight or over a period of thousands of years. I encourage you to research dating techniques yourself to see what their limitations are.

  9. I have just learned (via Bishop Hill) that commenter Paul_K also managed to criticise this statement both in the original article’s comments and in the comments to another article (when the original article’s comments were closed).

    Paul_K’s comments under the original article are here and here and part of his comment on the other article said:

    The statement which appeared in Fiona Harvey’s report of the IPSO was

    The oceans are more acidic now than they have been for at least 300m years, due to carbon dioxide emissions from burning fossil fuels, and a mass extinction of key species may already be almost inevitable as a result, leading marine scientists warned on Thursday.

    The source of this, the IPSO report, unambiguously referred to 300 million years, which period includes inter alia the Triassic, Jurassic and Cretaceous. It is not in any way controversial that atmospheric CO2 levels during the Triassic/ Jurassic were about 5 times higher than today; CO2 levels of greater than 3 times higher than today were apparent throughout the Cretaceous. See studies here for example http://droyer.web.wesleyan.edu/PhanCO2%28GCA%29.pdf.
    Unless someone has decided to rewrite geological history or to reject well established rules of physical chemistry, the oceans had a far lower pH during all of that time than they do today. The statement then is, as I said, contrary to all the scientific evidence. It is not even a controversial issue.”

    Thanks Paul, for drawing attention to these comments. I had not noticed them when I looked through the comment stream below the original article.

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  11. CO2 is the planet’s best friend….but try telling that to the middle class elite. They can’t even admit that the warming has stopped and is slipping away. CO2 levels were 13 times what they are today if you go back far enough so the Oceans would be long gone if CO2 caused serious acidification.

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