Attenborough enters deep water over coral

Climate Debate Daily reports that in the Guardian last Tuesday, the wonderful, inimitable David Attenborough warned alleged that carbon dioxide in the atmosphere is already above the level which condemns coral reefs to extinction in the future, adding the world had a “moral responsibility” to save corals.

This caught my attention. Already condemned to extinction? That is alarming.

But just a moment. Does he know the conditions corals have survived since they evolved? Does he know the current pH level of surface waters and the rate of change? Does he know that bleaching events cannot be linked to global warming? Has he heard of studies that show no change in marine biota even at pH levels ten times less alkaline than now?

Attenborough said “A coral reef is the canary in the cage as far as the oceans are concerned.” He explained that increasing atmospheric carbon dioxide acts on coral in two ways: it warms the water, causing coral “bleaching”, where the creatures lose the symbiotic algae they need to survive. It also makes the water more acidic, which apparently means the corals find it “difficult to prevent” their exoskeletons from dissolving.

“We’ve already passed a safe threshold for coral reef ecosystems in terms of climate change. We believe that a safe level for CO2 is below 350 parts per million,” said Alex Rogers, of the Zoological Society of London and International Programme on the State of the Ocean, who helped organise yesterday’s meeting.

They do not indicate why 350 ppmv is a “safe” level.

Attenborough said the plight of the corals was another example of why the control of carbon was so important to the world’s inhabitants. “Each ecological disaster or problem traces its cause back to carbon. To quibble about this is really fiddling while Rome burns. If we do not control the emission of carbon, this world is heading for a major catastrophe and this is one of the first to be staring us straight in the face.”

Rogers even suggests some geo-engineering techniques may be necessary to reduce atmospheric levels of carbon dioxide.

Now, I’m a big fan of David Attenborough. For many years I’ve taken enormous pleasure from hearing him talk about animals and plants around the globe and I greatly admire his enthusiasm for the creatures and plants we share the Earth with.

But as to dangerous global warming being caused by Man’s emissions of carbon dioxide he has been sorely misadvised. Why do I think so? There are three reasons.


Consider the level of carbon dioxide in the atmosphere when coral evolved. To hear Attenborough’s concerns, it would surely be logical to suppose that the level was lower than at present, since he says at the current rate of increase of atmospheric CO2 coral will be extinct within a few decades. So for the present levels to be so dangerous to coral, it must be accustomed to and require much lower levels, right?

Well, no, because when coral first appeared about 500 million years ago, in the Ordovician period, the concentration of carbon dioxide was 4500 ppmv—1100% higher than it is now—eleven times higher! And that was no sudden ‘spike’ that failed to last—that level was sustained for 70 million years until slowly declining to “only” 3000 ppmv. Since then, for most of the time it has remained about four times present levels until dropping “recently”—about a million years ago.

The likelihood of corals being harmed if CO2 levels rise to only 10% or 15% of what they evolved in and are accustomed to seems highly remote.


Bleaching events are natural and common, coral quickly recovers from them and anyway they cannot be linked with carbon dioxide, whether man-made or natural. Here is what Dr Walter Starck says about coral bleaching:

There is a widespread belief that AGW [Anthropogenic Global Warming] has resulted in increased coral bleaching and is a severe global threat to coral reefs. However, the high surface water temperatures associated with bleaching events are not the result of exceptionally high air temperatures. They result from extended periods of calm weather during which mixing from wave action ceases and surface water becomes exceptionally warm. Such warming is especially marked in very shallow water such as on reef flats. At the same time the absence of waves also eliminates the wave driven currents that normally flush the reef top.

Bleaching conditions require at least a week or more of calm weather to develop and this may happen every few years, only once in a century, or never, depending on geographic location. On oceanic reefs it is less common due to ocean swell and currents even in calm weather. In coastal areas it is more common due to the absence of swell and reduced currents.

Characteristic bleaching scars and isotope temperature records from coral cores commonly show evidence of past bleaching events going back thousands of years. There is no evidence for a recent increase in frequency and/or severity of bleaching events and nothing to link extended periods of calm winds with global warming.

No danger to coral can be deduced from this evidence.


A paper in Nature, Volcanic carbon dioxide vents show ecosystem effects of ocean acidification (Hall-Turner et al.), reported that by looking at natural sea bed vents of carbon dioxide, the researchers discovered that ocean pH became over ten times more acidic before the flora and fauna at the site were affected.

Dr J. Floor Anthoni describes the study thus:

“The study[, off Italy’s west coast,] shows that along a daily fluctuating gradient from normal sea water (pH=8.14) to acidic water (pH=6.57), species diversity suddenly drops at around pH=6.8 (about 20 times more acidic). It affects mainly calcareous algae, sea urchins, limpets, grazing snails and barnacles, which all produce limestone shells.

“More importantly, down to a pH of 7.2 (10 times more acidic), no measurable effect was found and no loss of biodiversity. Thus a doubling (pH=7.9) or quadrupling (pH=7.6) of CO2 concentrations in the atmosphere is not going to have any measurable effect on marine life.”

Ocean pH has fallen by an estimated 30% since pre-industrial times. Some alarming statements are being made about the extent of acidification, but people should know that the oceans are still a long way from actually being acidic (that is, with a pH of <7.0). Moreover, there is no possibility of the oceans (including the deep ocean) becoming acidic in the long term, since there’s not enough carbon dioxide in the atmosphere to accomplish it through this means.

The much-loved David Attenborough would be well advised to base his statements on sound science rather than simply joining in the popular, unthinking clamour against dangerous anthropogenic global warming. Environmentalism includes carbon dioxide in its list of pollutants only by abusing the facts.

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