How does rising atmospheric CO2 affect marine organisms?

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CO2 and Coral Calcification: Is the Tide of Pessimism About to Turn?
Volume 5, Number 12: 20 March 2002

For some time now, the ongoing rise in the air's CO2 content has been predicted to play havoc with earth's coral reefs in two different ways: (1) by stimulating global warming, which has been predicted to dramatically enhance coral bleaching, and (2) by lowering the calcium carbonate saturation state of seawater, which has been predicted to reduce coral calcification rates.

Most of our attention over the last few years has centered on the former of these concerns [see Coral Reefs (Bleaching) in our Subject Index]; but we have not been averse to delving into the latter topic as well [see Coral Reefs (Calcification) in our Subject Index], which we now do again in an attempt to get the world to realize what is really happening in this area. And what is really happening in this area is that a purely hypothetical concept is being promulgated as a fact of nature, which it clearly is not.

"Coral reef communities and organisms are stressed, potentially mortally," according to Buddemeier (2001); and one of the major reasons he gives for this assertion is the prediction - that's right, it's merely a prediction - that the ongoing rise in the air's CO2 content will significantly reduce rates of coral calcification around the world, even in the most pristine of places, since CO2 is well-mixed throughout the entire atmosphere. Suggestions of this possibility have been floating around for about a decade now; and the lion's share of the attention-grabbing articles have Buddemeier's name attached to them (Smith and Buddemeier, 1992; Buddemeier, 1994; Buddemeier and Fautin, 1996a,b; Gattuso et al., 1998), thereby apparently making him one of the chief planetary gurus on the subject.

Perhaps the most influential of these suggestions was one put forth in the pages of Science by Kleypas et al. (1999), of which, you can probably guess by now, Buddemeier was a co-author (the second of six, to be exact). In that study, Buddemeier and his colleagues calculated that coral calcification rates in the tropics should already have decreased by somewhere from 6 to 11% or more since 1880, as a result of the increase in atmospheric CO2 experienced between then and a couple of years ago; and they predicted that these reductions could reach 17 to 35% by 2100, as a result of expected increases in the air's CO2 content over the coming century.

The media attention that followed the publication of this high-profile article was a real circus. We were treated to headlines that literally trumpeted "CO2 Could Kill Coral" and "Great Barrier Reef Faces Death Knell." And the world - or at least the virtual world that climate alarmists and others of their ilk love to agonize about - has not been the same since.

In a review article the following year, we tried to draw attention to the tenuousness of these conclusions (Idso et al., 2000). Therein, we noted that coral calcification is more than a physical-chemical process that can be described by a set of well-defined equations and constants, reiterating the well-known fact that coral calcification is a biologically-driven physical-chemical process that may not be amenable to explicit mathematical description. Specifically, we noted that "the photosynthetic activity of zooxanthellae is the chief source of energy for the energetically-expensive process of calcification" and that much evidence suggests that "long-term reef calcification rates generally rise in direct proportion to increases in rates of reef primary production," suggesting that "if an anthropogenic-induced increase in the transfer of CO2 from the atmosphere to the world's oceans were to lead to increases in coral symbiont photosynthesis - as atmospheric CO2 enrichment does for essentially all terrestrial plants - it is likely that increases in coral calcification rates would occur as well." We also noted that "the calcium carbonate saturation state of seawater actually rises with an increase in temperature [such as occurs during dreaded global warming], significantly countering the direct adverse oceanic chemistry consequences of an increase in atmospheric and/or hydrospheric CO2 concentration," which led us to ultimately warn that "the negative predictions of today could well be replaced by positive predictions tomorrow."

So who, or what, do you trust: the thinking of one of the world's gurus on the subject? Or the thinking of us novices? We say, why trust anybody's thinking? Especially when long-term real-world data sets are available ... all two of which we will now review for you.

The first of these important data sets was already available when we wrote our review of the subject. It was developed by Lough and Barnes (1997) from a detailed analysis of annual coral growth layers evident in several cores retrieved from colonies of long-lived Porites corals growing at 35 different locations on Australia's Great Barrier Reef. The several sampling sites employed in their research program stretched from 9 to 23 S latitude and provided a wealth of information about coral calcification rate for every year since the late 15th century.

In analyzing their data, the two scientists discovered there was a statistically significant correlation between coral calcification rate and local water temperature, such that a 1C increase in mean annual water temperature increased mean annual coral calcification rate by about 3.5%. Nevertheless, they report there were "declines in calcification in Porites on the Great Barrier Reef over recent decades." They are quick to point out, however, that their data depict several extended periods of time when coral growth rates were either above or below the long-term mean, cautioning that "it would be unwise to rely on short-term values (say averages over less than 30 years) to assess mean conditions."

As an example of this fact, they report that "a decline in calcification equivalent to the recent decline occurred earlier this century and much greater declines [our italics] occurred in the 18th and 19th centuries." Over its entire expanse, in fact, the Lough and Barnes data set indicates that "the 20th century has witnessed the second highest period of above average calcification in the past 237 years," which is not exactly what one would expect in light of (1) how dangerous high water temperatures are often said to be to corals, (2) the climate-alarmist claim that earth is currently warmer than it has been at any other time throughout the entire past millennium, and (3) the fact that the air's CO2 content is higher than it has been for an even longer time than that.

The second and newest of the two long-term, real-world, coral-calcification data sets comes to us courtesy of Bessat and Buigues (2001). It was derived from a core extracted from a massive Porites coral head on the French Polynesian island of Moorea that covered the period of time from 1801-1990. The scientists say they undertook the study because "recent coral-growth models highlight the enhanced greenhouse effect on the [predicted] decrease of calcification rate." Rather than rely on theoretical calculations, Bessat and Buigues decided they wanted to ask some actual real-world corals what they though about this hypothesis, thinking that the records preserved in their hardened skeletons "may provide information about long-term variability in the performance of coral reefs, allowing unnatural changes to be distinguished from natural variability," which we know can be very substantial, as indicated by the work of Lough and Barnes.

So what did Bessat and Buigues find? First of all, they found that a 1C increase in water temperature increased coral calcification rate at the site they studied by fully 4.5%. Then they found that "instead of a 6-14% decline in calcification over the past 100 years [as] computed by the Kleypas group, the calcification has increased, in accordance with [what] Australian scientists Lough and Barnes [found]." They also observed patterns of "jumps or stages" in the record, which were characterized by an increase in the annual rate of calcification, particularly at the beginning of the past century "and in a more marked way around 1940, 1960 and 1976," stating once again that their results "do not confirm those predicted by the Kleypas et al. (1999) model."

So there you have it. Out in the real world of nature, corals don't seem to be aware of the climate-alarmist decree that their rates of calcification are supposed to be declining in response to the ongoing rise in the air's CO2 content; and no matter how many papers the Buddemeiers of this world may write to the contrary, earth's corals will likely continue to do their own thing and keep right on growing at current or even accelerated rates, unless some of the very real and serious localized threats to their existence overwhelm their uncanny innate ability to cope with whatever the non-anthropogenic world periodically sends their way.

Dr. Sherwood B. Idso
Dr. Keith E. Idso
Vice President

Bessat, F. and Buigues, D. 2001. Two centuries of variation in coral growth in a massive Porites colony from Moorea (French Polynesia): a response of ocean-atmosphere variability from south central Pacific. Palaeogeography, Palaeoclimatology, Palaeoecology 175: 381-392.

Buddemeier, R.W. 1994. Symbiosis, calcification, and environmental interactions. Bulletin Institut Oceanographique, Monaco 13: 119-131.

Buddemeier, R.W. 2001. Is it time to give up? Bulletin of Marine Science 69: 317-326.

Buddemeier, R.W. and Fautin, D.G. 1996a. Saturation state and the evolution and biogeography of symbiotic calcification. Bulletin Institut Oceanographique, Monaco 14: 23-32.

Buddemeier, R.W. and Fautin, D.G. 1996b. Global CO2 and evolution among the Scleractinia. Bulletin Institut Oceanographique, Monaco 14: 33-38.

Gattuso, J.-P., Frankignoulle, M., Bourge, I., Romaine, S., Buddemeier, R.W. 1998. Effect of calcium carbonate saturation of seawater on coral calcification. Global and Planetary Change 18: 37-46.

Idso, S.B., Idso, C.D. and Idso, K.E. 2000. CO2, global warming and coral reefs: Prospects for the future. Technology 7S: 71-94.

Kleypas, J.A., Buddemeier, R.W., Archer, D., Gattuso, J.-P., Langdon, C. and Opdyke, B.N. 1999. Geochemical consequences of increased atmospheric carbon dioxide on coral reefs. Science 284: 118-120.

Lough, J.M. and Barnes, D.J. 1997. Several centuries of variation in skeletal extension, density and calcification in massive Porites colonies from the Great Barrier Reef: A proxy for seawater temperature and a background of variability against which to identify unnatural change. Journal of Experimental and Marine Biology and Ecology 211: 29-67.

Smith, S.V. and Buddemeier, R.W. 1992. Global change and coral reef ecosystems. Annual Review of Ecological Systems 23: 89-118.