A Shell Game Behind Ocean Acidification?

This is the story of how field data showing higher CO2 concentrations in the past is what probably lies behind the increasingly louder alarm calls about ocean acidification in the future.

The story ends with the “Monaco Declaration” and “more then 150 top marine researchers” voicing “their concerns [that] he world’s marine ecosystems risk being severely damaged by ocean acidification unless there are dramatic cuts in CO2 emissions“, as per this recent BBC story.

The story starts with two articles by “Pearson and Palmer” in Science (1999) and Nature (2000):

(1) Pearson, P.N. and Palmer, M.R. 1999. Middle Eocene seawater pH and atmospheric carbon dioxide concentrations. Science 284: 1824-1826

(2) Pearson, P.N. and Palmer, M.R. 2000. Atmospheric carbon dioxide concentrations over the past 60 million years. Nature 406: 695-699

According to (1) , “[…] construction of a pH profile for the middle Eocene tropical Pacific Ocean shows that atmospheric pCO2 was probably similar to modern concentrations or slightly higher”.

The abstract in (2) reads “[…] We estimate CO2 concentrations of more than 2,000 p.p.m. for the late Palaeocene and earliest Eocene periods (from about 60 to 52 Myr ago) […] Since the early Miocene (about 24 Myr ago), atmospheric CO2 concentrations appear to have remained below 500 p.p.m. and were more stable than before, although transient intervals of CO2 reduction may have occurred during periods of rapid cooling approximately 15 and 3 Myr ago“.

Lest we forget, it is commonly accepted that CO2 changes follow temperature. Anyway, the two Pearson and Palmer papers show:

  • a +5C warmer Earth than today during the Eocene, for an estimated 385ppmv of CO2 (min:180; max:550)
  • hence, either an extreme climate sensitivity or more likely “that the global cooling since the Eocene was not driven primarily by changes in pCO
  • large variations in atmospheric CO2 concentrations not exactly associated to incredible bloomings or mass extinctions in marine life

It would appear obvious that the above is no basis for any concern about marine life and acidification caused by increased CO2 concentrations. So how does one get from start to apparently contradictory end?

Here’s how. Let’s trace the path backwards.

[i] On the side of the BBC article, follow the link to “The Ocean Acidification Network“.

[ii] Click on “How is the ocean acidity changing?” and look at the graph.

[iii] Note the huge swing 1800-2000, covering almost the whole range experienced during the past 25 million years.

[iv] The caption says “From Pearson and Palmer, adapted by Turley et al. and from the Eur-Oceans Fact Sheet No. 7, “Ocean Acidification – the other half of the CO2 problem”, May 2007“.

[v] The Pearson and Palmer reference is (2) above. The Turley reference is:

(3) Turley, C., et al. (2006), Reviewing the Impact of Increased Atmospheric CO2 on Oceanic pH and the Marine Ecosystem, in Avoiding Dangerous Climate Change, 65-70, Cambridge University Press

[vi] Parts of that book are available via Google, and in particular most of the Turley et al. contribution, with a page with that exact graph.

[vii] Note the respective sources for the values displayed:

  • Points before 1800 are defined in (3) as “Past…variability of marine pH” with a reference once again to Pearson and Palmer from 2000 (once again, reference (2) above).
  • The values for 1800 and 2000 are defined as “contemporary variability of marine pH” (i.e. the huge swing as per step [iii] above).
  • The 2050 and 2100 diamonds are “model derived…based on IPCC mean scenarios“.

[viii] What could those models be? Look at “Ocean Acidification” on Wikipedia. The main reference for future predictions is this Orr et al.’s article in Nature in 2005:

(4) Orr, J.C. et al. Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms, Nature 437, 681-686 (29 September 2005) (full text)

[ix] Look at the caption of figure 1 in the full text. Orr et al. write that they estimate “pre-modern DIC” (dissolved inorganic carbon) “by subtracting data-based anthropogenic DIC […] as well as by subtracting model-based anthropogenic DIC“.

[x] The authors refer the readers to the “Supplementary Info” for their article (full text). Therein they mention this 2004 Science article:

(5) Sabine C.L. et al., “The Oceanic Sink for Anthropogenic CO2“, Science 16 July 2004 Vol. 305. no. 5682, pp. 367 – 371

[xi] Interestingly, Sabine et al. write the following in response to a comment about (5): “Our assessment of the impact of climate change on the ocean carbon inventory applies only to the past 200 years“.

[xii] In other words, the estimates done by Orr et al. for 1800 are at the very edge of visibility.

This means that the huge swing as of step [iii] may actually be an artifact of analysis.


In summary:

  • even if past data suggests that the oceans can cope reasonably well with very large variations in atmospheric CO2 concentrations (1) (2),
  • that same data is taken as evidence of future ocean acidification,
  • using a graph from an article that estimates ocean pH between 1800 and 2100 (3)
  • based on a work that compares pre-modern and modern marine CO2 concentrations (4)
  • according to another work whose results barely cover the whole period (5).

A swift sleight of hand in some kind of peer-reviewed shell game, perhaps?