Can we keep discussions about ocean acidification honest?


In his article, ‘Taking Fears of Acid Oceans with a Grain of Salt’, Matt Ridley recycles the standard arsenal of invalid climate ‘skeptic’ arguments and tactics, but applies them to ocean acidification, the lesser known global impact from rising atmospheric CO2 concentrations. 

The result is an exercise in obfuscation.  As a scientist working on these issues for the past five years, I was struck by several gaping holes (and inaccuracies) in his piece – taking liberty to manipulate facts in order to misrepresent them.

For instance, he plays unproductive semantic games, arguing that because ocean pH is not predicted to fall below the ‘neutral point’ of 7.0, the term ‘ocean acidification’ is a misnomer.  This ignores the fact that scientists refer to a drop in pH as ‘acidification’, regardless of where you are on the scale.  The term is simply used to describe the direction of change. 

He also makes the same (tired) mistake as those who confuse ‘weather’ for ‘climate’ when he equates short-term natural variation in pH with that of long-term change in the average pH of the world’s oceans.  These are not equivalent.  That’s like saying there is a drought because it’s been a dry week, even if rainfall is above average for the year.

Contrary to Ridley’s arguments, scientists can measure and differentiate between these two types of variation—and organisms do not experience short-term and long-term variations in the same manner.  That is why the sugar maple in my backyard survived today’s 20 degree F fluctuation in air temperature – but the Connecticut population is unlikely to successfully compete with oaks and survive the predicted 4-6 degree F rise in average regional temperature over the next century.

Ridley goes on to raise irrelevant facts by discussing pH and freshwater as a comparison to ocean acidification – but there is no relationship here.  While the natural variation of pH in fresh systems is high, it has no bearing on the oceans, or the survival marine organisms.

Worst of all, Ridley flatly misstates research conclusions when he claims that “laboratory experiments find that more marine creatures thrive than suffer when carbon dioxide lowers the pH level to 7.8.” The opposite is true and you can see for yourself:

Hendriks et al., 2010

Kroeker et al., 2010

Gattuso J.P., et al., 2011.

Ridley is correct in pointing out that not all marine organisms will suffer from an increase in ocean acidity. Some, in fact, will likely thrive (e.g., seagrasses).  However, he omits the conclusions from the studies he alludes to.  In regions with naturally occurring higher levels of acidity, resulting from volcanic venting of CO2, researchers have found substantial losses in marine biodiversity at the same pH levels that are predicted at the end of this century. Specifically there was a 30% decline in overall species richness in Italy (Hall-Spencer et al., 2008) and a 39% decline in hard coral species richness in the Indo Pacific (Fabricius et al., 2011). 

If these naturally more acidic sites portend the future of marine ecosystems, does a 30% loss in species diversity constitute a catastrophe for the world’s oceans?  It does for people who have come to rely on the affected organisms for income or food. 

There are local economies in the United States – and around the world - that rely disproportionately on species that show vulnerabilities to ocean acidification.  For example, New Bedford, Massachusetts, which has ranked highest among U.S. ports for values of seafood landings over the past decade, gets 77% of its total landings revenues from sea scallops ($306 million in 2010) (NOAA, 2011).  In laboratory experiments, a close relative, the Atlantic bay scallop demonstrates a drop in larval survivorship and impaired shell development as ocean acidity increases (Talmage and Gobler, 2010). And in the Pacific Northwest, oyster hatcheries are already seeing the impact to larval oysters – leaving owners worried about their livelihoods. This alone is cause for concern. 

Taking ocean acidification ‘with a grain of salt’ would be a mistake.  At the very least, experts and the U.S. government should identify economically vulnerable ‘hot spots’ and begin to monitor the chemical and biological changes that are occurring off our coasts. 

 Literature Cited:

Fabricius K. E., Langdon C., Uthicke S., Humphrey C., Noonan S., De’ath G., Okazaki R., Muehllehner N., Glas M. S. & Lough J. M., 2011. Losers and winners in coral reefs acclimatized to elevated carbon dioxide concentrations. Nature Climate change 1:165-169.

Gattuso J.-P., Bijma J., Gehlen M., Riebesell U. & Turley C., 2011. Ocean acidification: knowns, unknowns and perspectives. In: Gattuso J.-P. & Hansson L. (Eds.), Ocean acidification, pp. 291-311. Oxford: Oxford University Press.

Hall-Spencer J. M., Rodolfo-Metalpa R., Martin S., Ransome E., Fine M., Turner S. M., Rowley S. J., Tedesco D. & Buia M.-C., 2008. Volcanic carbon dioxide vents show ecosystem effects of ocean acidification. Nature 454:96-99.

Hendriks IE, Duarte CM, Alvarez M (2010) Vulnerability of marine biodiversity to ocean acidification: A meta-analysis. Estuar Coast Shelf Science 86: 157–164.

Kroeker KJ, Micheli F, Gambi MC, Martz TR (2011) Divergent ecosystem responses within a benthic marine community to ocean acidification. P. Natl. Acad. Sci. USA: doi/10.1073/pnas.1107789108.

NOAA, 2011.  Fisheries of the United States:  2010.  National Marine Fisheries Service/Office of Science and Technology

Talmage, S. C. and Gobler, C. J.  Effects of past, present, and future ocean carbon dioxide concentrations on the growth and survival of larval shellfish.  P. Natl. Acad. Sci.