Coral reefs and climate change. Close to catastrophic collapse?
Professor Alexandra Grutter, University of Queensland, sent me this:
The coral reef crisis: The critical importance of less than 350 ppm CO2
By Veron et al. 2009. Marine Pollution Bulletin 58, 1428-1436.
“Abstract
Temperature-induced mass coral bleaching causing mortality on a wide geographic scale started when atmospheric CO2 levels exceeded 320 ppm. When CO2 levels reached 340 ppm, sporadic but highly destructive mass bleaching occurred in most reefs world-wide, often associated with El Niño events. Recovery was dependent on the vulnerability of individual reef areas and on the reef’s previous history and resilience. At today’s level of 387 ppm, allowing a lag-time of 10 years for sea temperatures to respond, most reefs world-wide are committed to an irreversible decline. Mass bleaching will in future become annual, departing from the 4 to 7 years return-time of El Niño events. Bleaching will be exacerbated by the effects of degraded water-quality and increased severe weather events. In addition, the progressive onset of ocean acidification will cause reduction of coral growth and retardation of the growth of high magnesium calcite-secreting coralline algae. If CO2 levels are allowed to reach 450 ppm (due to occur by 2030–2040 at the current rates), reefs will be in rapid and terminal decline world-wide from multiple synergies arising from mass bleaching, ocean acidification, and other environmental impacts. Damage to shallow reef communities will become extensive with consequent reduction of biodiversity followed by extinctions. Reefs will cease to be large-scale nursery grounds for fish and will cease to have most of their current value to humanity. There will be knock-on effects to ecosystems associated with reefs, and to other pelagic and benthic ecosystems. Should CO2 levels reach 600 ppm reefs will be eroding geological structures with populations of surviving biota restricted to refuges. Domino effects will follow, affecting many other marine ecosystems. This is likely to have been the path of great mass extinctions of the past, adding to the case that anthropogenic CO2 emissions could trigger the Earth’s sixth mass extinction.”
Full report here: http://dx.doi.org/10.1016/j.marpolbul.2009.09.009
October 16th, 2009 at 9:45 am
Yes, policy is the fate! - “The earth´s sixth mass extinction due to anthropogenic CO2 emissions”, would it be a tragedy in the classical sense? Certainly not. The ruin would neither be due to our inability to cope with unfavorable circumstances nor to the inevitability of being on the horns of a dilemma. While talking about the undeservedly high estimation and popularity of the numerous French “Schicksalstücke” built on the concept of tragic fate, Napoleon said to Goethe deeply annoyed about their blatant inveracity: “(Tragic fate?) It belongs to a darker age. What is that supposed to achieve? Policy is the fate!” - It sounded true 200 years ago; today it is self-evident. The only difference is that during the Napoleonic era the holders of power were relatively few aristocrats, strongmen and dictators having an eye to their own interests; but now it is basically the people. And everything that happens nowadays on earth (and especially to her) is therefore strongly related to everybody´s vital interests. But as the many doomed People´s Republics isn´t the beautiful and unique People´s Earth likely to be doomed as well? There are many countries man could experiment with without damaging mankind as a whole, but there is but one world that definitely can´t tolerate a single similarly profound environmental change without suffering a huge loss in ecologocal stability, species diversity, beauty and overall emotional meaning. Will she remain in its splendor and habitability?Only time will tell - but then who will listen?
October 19th, 2009 at 9:51 am
Look up the temperatures commonly reached by surface waters in the Persian Gulf. The reefs there survive. If some coral species find it difficult to survive in higher water temperatures, they will be replaced by more robust species. Life adapts, life gets by.
The evidence for ocean alkalinisation is based on poor modelling of the thermodynamics of gas transfer across the air/ocean interface.
Organisms decide what ions enter their bodies and the conditions under which they enter; biomineralisation achieves things that are ludicrous if you just consider the composition of the environment.
Alkalinisation that dissolves dead coral near the surface will surely be balanced by heating at depth that makes calcium carbonate stable.
I understand there were reefs during the Mesozoic, when atmospheric carbon dioxide levels were consistently above 2000 ppm.
If you accept Veron’s article at face value, it is a counsel of despair, because there is *nothing* short of genocide or invasion by benevolent aliens that can cap carbon dioxide levels below 450 ppm.
Unfortunately the world became addicted to ‘eat, drink, and be merry, for tomorrow you die’ during the bad old days of 1945-1991, and since then has been desperate to find some new catastrophe to maintain its fin-de-siecle mood of decadent panic. IMHO…
October 19th, 2009 at 10:53 am
In the Mesozoic, reefs were totally different, as were general conditions in the oceans. Replacement of these old reefs took millions of years. I doubt that we will have that time!
Concerning modelling: I can only say what I said earlier (somewhere): we cannot be sure about anything but we are not in a position to do nothing. I tend to believe that models presented to us are possibly (and perhaps likely) more benign than what they should be. The authors of the article on reefs I refer to are all distinguished scientists in their field, and I assume that they know what they are talking about. After all, coral bleaching has already wiped out significant proportions of once existing reefs, closely correlated with rising ocean temperatures. Even the hardiest corals cannot survive at certain excessive temperatures. Evolution to replace extinct species may take a very long time (at evolutionary scales).
October 19th, 2009 at 5:11 pm
I don’t know where these reefs ‘wiped out by coral bleaching’ are.
This book extract from 2004 cites the Persian Gulf as a region where the greatest proportion- 65% - of reefs have been ‘destroyed’, but <a This more recent report, while not painting a pretty picture, shows significant recovery at all reefs not impacted by coastal development and a replacement- in decades, not millions of years- of less robust coral species by more robust ones. This within the context of a history of dramatic bleaching events. Is it possible coral bleaching in reefs is no worse (or better) than fire in forests and just as important for maintaining the biodiversity we see?
Parenthetically, I never assume anyone I talk to knows what they are talking about, no matter how distinguished they are! I am too pathetically aware of the vast yawning gulfs of ignorance in my own knowledge of the matters I am supposed to be an expert in…
October 19th, 2009 at 6:45 pm
Yes indeed, although coral destruction due to bleaching was world-wide, it was most prominent in the Indian Ocean (although I am not up to date with the geography of bleaching events and the Caribbean also, I believe, was quite severely impacted). And indeed, there has been recovery, however you can hardly project from a “relatively” minor event at the beginning of a possible catastrophe to future much larger events. So far, all coral species have survived and resettlement in those areas that had been affected was possible by larvae spreading from elsewhere (e.g., possibly even from the Great Barrier Reef to the Persian Gulf). But this may (and will) not be possible when destruction is on a much larger scale. - Comparing bleaching with bush fires: this would be justified only if events are relatively minor and damage can be repaired by recovery in situ or immigration. As it looks, we may soon be beyond that point. - Concerning expertise of “experts”: here I mus agree, from my own experience I must say that fools are common everywhere, and probably not rarer among academics than other groups. Nevertheless, I think it would be foolish to reject action on climate change because some “experts” may be wrong. It seems to me that evidence for urgent action is strong, although I wish I was wrong.
October 21st, 2009 at 3:41 pm
In the Mesozoic, reefs were totally different, as were general conditions in the oceans.
From my reading it seems that the current reef-building scleractinian corals occupied that niche after the Triassic, so reefs were not totally different. During the Jurassic the tropical belt extended to 55 degrees north, a time not only of high atmospheric carbon dioxide concentrations but spectacular and extensive carbonate deposition worldwide. I think there is absolutely no evidence from geology in support of these predictions of catastrophic collapse.
So far, all coral species have survived and resettlement in those areas that had been affected was possible by larvae spreading from elsewhere
The important point is that this documented resettlement is not from thousands of miles away, but from a few vertical metres away, because that distance in the water column is a significantly different environment. And that this resettlement was observed in a few years after very dramatic bleaching events.
Nevertheless, I think it would be foolish to reject action on climate change because some “experts” may be wrong. It seems to me that evidence for urgent action is strong, although I wish I was wrong.
This brings us to the threshold of an argument in which I have a much greater emotional investment and feel I stand on much stronger ground. (I think the balance of probability is that the risks of anthropogenic climate change have been grossly overstated, and I have a reflexive urge to shout ‘white!’ when everyone around me is shouting ‘black!’, but I have come late and tentatively to a ’skeptic’ position).
Let us assume something should be done urgently. What do you think should be done?
October 23rd, 2009 at 10:19 am
First, thanks for drawing my attention to a sloppy response of mine: I was referring to pre-Triassic (Paleozoic) reefs when I said “totally different”.
Relatively fast recovery was possible because damage was still relatively minor. If damage will be on a much larger scale, recovery due to replacement in situ (from corals deeper down) or from other reefs will become progressively more difficult and finally impossible.
It seems to me that the authors of the article have given a very balanced and cautious account. A few quotes show this:
“full range of biological responses incompletely understood”
As the authors point out, over the last 240 million years, reefs have been repeatedly decimated (have a look at a number of papers of geologists/paleontologists on changes in marine benthic diversity since the Triassic!! e.g. Jablonski) and
“once lost, reefs can take thousands to milions of years to reestablish” (as above).
“perhaps most importantly, there is no evidence that reefs have ever experienced true parallels to today’s anthropogenically driven combination of stressors. At the rate at which these stressors are currently compounding we are going into uncharted waters”.
The authors do not just consider one stressor, but repeatedly emphasize that multiple stressors and synergies must be considered. These include sea level rises, increases in high-energy storms, fisheries impact, and water quality (runoffs etc.).
All these stressors have been well examined using empirical data (although much remains to be done), as well as modelled (although any model of course has its flaws and we cannot be absolutely sure).
You ask for what should be done. As far as reefs are concerned, I would suggest to have a look at the last section in the article “remedial action”, But of course reefs are only one aspect of the problem. Tropical rain forests, forests in general etc. etc. also must be considered, and here I would suggest to accept the advice given by international groups of scientists who have worked on this problem.
As I said earlier: we cannot afford to wait, even if we are not absolutely sure: the stakes are too high. Is it worth risking the future of our children because we insist on further and further “improving” our life style ?
October 23rd, 2009 at 10:22 am
I forgot to include among stressors: acidification, of course.
October 23rd, 2009 at 5:59 pm
The acceptance of the authors that reducing atmospheric carbon dioxide will “demand maintaining, enhancing and probably creating carbon dioxide sinks” and consider various planetary scale geoengineering schemes is very refreshing. I am keen to support this sort of work going forward.
October 26th, 2009 at 7:29 pm
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