Marohasy is correct to suggest that moderate global warming may well be good for the GBR, or at least not a significant threat. Although many scientists such as my colleague Terry Hughes (that CJ Morgan mentions) believes that the GBR is seriously threatened, there are others of us who look at the evidence and come to a different conclusion. The science indicates the following.
• The warming that has already occurred over the last 100 years has increased the rate of growth of massive corals.
• The species we have on the GBR are also found in much warmer water in PNG.
• Growth rates of corals increase linearly with temperature up to temperatures significantly higher than those that the GBR experiences.
• The only corals on the QLD coast that are temperature stressed are those of Moreton Bay and that is because they are in an environment that gets too cold in winter. They will certainly benefit from global warming.
• In the recent bleaching events, most of the GBR did not bleach and almost all that did bleach has almost completely recovered.
• Recent research here at JCU also indicates that corals are able to take on different strains of Zooxanthellae after bleaching events and these "low octane" strains make them grow more slowly but protect against future bleaching.

Although in my view moderate increases in temperature are good for the GBR there is reason to worry about the effect of changes in pH on coral growth. It will be interesting to see what science will eventually say about this.

On other issues, the reef is also only mildy affected by runoff or fishing. It is a huge rapidly flushed system and most of it is 100 km from the coast. The population adjacent to its 2000km length is only 0.5 million compared with many hundred times that number for the similarly sized Caribbean. The northern most 800 km has a few hundred people living close to it. There are many more threatened ecosystems to worry about than the GBR.

Peter Ridd, Physics, James Cook University

That's 'Jennifer Marohasy', billissey.

The ocean acidification scare is bunk for some very sound reasons.

1 It is dependent on, at least, a doubling of atmospheric CO2 which not even the barking mad have suggested will occur within 30 years as claimed by the ACF.
2 Even a doubling by 2100 is dependent on no substitution of nuclear for coal etc, and assumes that India, Africa and China will not only achieve fully developed status by 2100, but do so under the USA development model rather than the Japanese model that produces much less CO2.
3 The doubling of atmospheric CO2 is dependent on a slow rate of absorption of CO2 by the oceans which is supposed to cause the build up in the atmosphere but for acidity to get within cooee of harming the GBR in 30 years the ocean absorption would need to be faster than the projected emission rate.
4 The modelling done by the UK Royal Society on ocean acidity assumed that the mixing of CO2 in sea water only took place in the top 100 metres. The average ocean depth is actually 4000 metres so the CO2 was assumed to be concentrated in the top 2.5% of ocean volume.
5 This ignored the fact that eddies from the Gulf Stream reach depths of 1.2km and also ignored the presence of thermohaline circulation of deep ocean water. They also pretended that deep ocean upwelling, like the one that produces EL Ninos, don't exist.

The general view is that complete ocean circulation needs about 400 years to complete. So a modelled projection of ocean CO2 absorption over 100 years must assume that CO2 will be absorbed by 25% of the entire ocean volume.

The UKRS used only 2.5% of ocean volume or a tenth of the correct volume to claim a concentration of acidifying CO2 that is 10 times stronger than the correct result.

The "acid ocean" threat to the reef is as weak as water.

Re the global warming aspects of this topic, authoritative groups of scientists and economists have just released critiques of the science and economics of the Stern Review. In summary, they conclude that the Review fails to present an accurate picture of scientific understanding of climate change issues, and will reinforce ill-informed alarm about climate change. Two interrelated features of the Stern Review are that it greatly understates the extent of uncertainty as to possible developments, in highly complex systems that are not well understood, over a period of two centuries or more; and its treatment of sources and evidence is persistently selective and biased. These twin features have combined to make the Review a vehicle for speculative alarmism. In the judgement of the authors of the Dual Critique, the Stern Review mishandles data; gives too little attention to actual observation and evidence, as distinct from the results of model-based exercises; and takes no account of the failures of due disclosure, and the chronic limitations of peer reviewing, that have been characteristic of work relating to climate change which governments have commissioned and drawn on. As to specifically economic aspects, the authors note among other weaknesses that the Review systematically overstates projected costs of climate change, partly though by no means wholly as a result of its failure to acknowledge the scope for long-term adaptation to possible global warming; underestimates the likely cost—including to the world’s poor—of the drastic global mitigation programme that it calls for; and proposes worldwide adoption of a specially low rate of interest for discounting the costs and benefits of mitigation, on the basis of inadequate analysis and without regard for the problems and risks that would result. So far from being an authoritative guide to the economics of climate change, the Stern Review is deeply flawed. It does not provide a basis for informed and responsible policies. (www.world-economics-forum.com)

So let’s not get over-excited at this stage. The above is the abstract for the paper – I also have some points from it.

I agree that coral reefs will generally benefit from warmer conditions….if you define ‘benefit’ as bigger, more robust and more rapidly growing.

But how will climate change / temperature increase really affect the ecosystems on the reef?

Higher temperatures will favour vigorous species and disadvantage species adapted to marginal conditions. Thus, the species balance will change with less competitive species being disadvantaged and perhaps eliminated from large areas, or perhaps even rendered extinct.

Our knowledge of the intricacies of ecology on the Great Barrier Reef is not good enough to know just what the impacts of climate change might be for some species. But if it is anything like terrestrial ecosystem mosaics (and basically it is), then increasing temperature is not going to have an overall positive effect, it is simply going to lead to a change in the balance, which will favour some species and threaten others.

Climate change very likely presents the illusion of increased health and vigour on the GRB while promulgating grave struggles for some species and a greatly increased level of ecological turmoil.

Aaaargh GRB my foot. That should be GBR of course.

I think Dr Peter Ridd presents a pretty realistic overview of the effects of climate change, and of runoff and other land-based activities on the GBR.

But given that these impacts are slight, it is very hard to imagine that climate-change-induced pH change could be a significant factor, especially in such as “rapidly flushed system” in the open ocean where any pH changes on the reef would surely be diluted into insignificance.