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Coral Calcification on the Great Barrier Reef
Volume 12, Number 1: 7 January 2009

Over the last few days there has been a great fuss in the news about a recent decline in the calcification rates of Porites corals on Australia's Great Barrier Reef, which is being widely attributed to the ongoing rise in the atmosphere's CO2 content leading to ocean acidification, helped along by periods of debilitating heat stress caused by CO2-induced global warming. These reports are based on an original research paper written by De'ath et al. (2009), which appeared in the journal Science in its first issue of the new year.

The media's regurgitations of the three scientists' findings have included some ominous declarations. The headline of a BBC News report, for example, says "coral reef growth is slowest ever," while a Sky News headline says "Barrier Reef coral growth 'will stop'." And ABC News actually tells us when it might stop, concluding their report by stating that the research paper's senior author says "coral growth could hit zero by 2050."

Do you think these statements might possibly be slight exaggerations? In fact, do you even have to think about it at all? If you do, well, that's another story. So ...

... let's take the first claim first: "coral reef growth is slowest ever." Ever, in this context, is a very long time, suggesting, in fact, for as long as there have been corals to grow. So, no, it can't possibly be right. Or at least it can't be known to be right. What we do know, however, is that corals have been around for quite a long time, even longer than the BBC News has been around, and even longer than all of mankind has been on the scene. In fact, the scleractinian corals, which are the major builders of the reefs of today, have been around some 200 million years, during most of which time both the atmosphere's CO2 concentration and its temperature were much greater than they are today, which should immediately raise a red flag about the proffered cause of the recent decline in reef growth.

But to continue, De'ath et al. are much more circumspect than are others when it comes to describing the uniqueness of their findings, stating that the 14% drop in Porites calcification rate they detected on the Great Barrier Reef from 1990 to 2005 (actually from 1970 to 2005, if one goes by their graph of the phenomenon) "is unprecedented in at least the past 400 years," which is indeed what their data show. But if one follows their calcification history back in time a mere 33 more years, from 1605 to 1572 -- when the air's CO2 concentration was more than 100 ppm less than what it is today and, therefore, was supposedly so much more healthier for corals (if you believe climate alarmists!) -- the coral calcification rate at that earlier time is seen to have been approximately 21% lower than what it was at its 20th-century peak.

Another way of looking at De'ath et al.'s data is to realize that from 1572 to 1970 Porites calcification rates on the Great Barrier Reef rose, by about 27%, as the "twin evils" of the radical environmentalist movement -- atmospheric CO2 concentration and air temperature -- rose concurrently, after which calcification rates declined, but by a much smaller 14%, as these same air temperature and CO2 trends continued, further obfuscating the issue.

So why would anyone believe that the calcification decline of 1990 to 2005 implies that Porites coral growth "will stop," and that the end will come "by 2050"? They believe it because certain scientists (such as James Hansen) and politicians (such as Al Gore) imply much the same thing, as even De'ath et al. do. But when they feel compelled to be as correct and as true to their data as possible, such as when writing in Science, the three researchers from the Australian Institute of Marine Science clearly state that "the causes for the Great Barrier Reef-wide decline in coral calcification of massive Porites remain unknown."

And when the causes of a 15-year decline in coral calcification rate are admitted to be unknown, it seems foolish indeed to predict, not only that the decline will continue, but that it will lead all the way to the demise of the studied coral, and especially at a specified future date, which, we might add, De'ath et al. appropriately do not do in their Science paper.

Clearly, the issue is far from settled, as Pennisi (2009) states in a commentary on the new paper in the same issue of Science, and as De'ath et al. themselves suggest, even though they have their opinions about the matter and we have ours. On that we are unanimous.

Sherwood, Keith and Craig Idso

De'ath, G., Lough, J.M. and Fabricius, K.E. 2009. Declining coral calcification on the Great Barrier Reef. Science 323: 116-119.

Pennisi, E. 2009. Calcification rates drop in Australian reefs. Science 323: 27.