The Australian Government has set a 2020 target of reducing direct national greenhouse gas emissions by between 5 to 15% and thereby aiming at a global scenario that would stabilise global atmospheric greenhouse gases at around 510 to 550 parts per million carbon dioxide equivalents (ppm CO2-e) by the end of the century.
Heogh-Guldberg et al (2007) illustrated what these targets mean for the Great Barrier Reef and much of the marine ecosystem in the following series of pictures. Picture A on the left represents current conditions for corals across much of the GBR. Picture C on the right represents the conditions under the atmosphere being aimed for by the Australian Government.
The Carbon Pollution Reduction Scheme White Paper, released on 15 December 2008, does not acknowledge the expected impacts on the Great Barrier Reef if its global stabilisation targets are achieved but draws heavily on the economic analysis of Professor Ross Garnaut.
Garnaut (2008a: 38) was brutally frank in his supplementary draft report: “The [strategy of stabilising at 550 ppm CO2-e] would be expected to lead to the destruction of the Great Barrier Reef and other coral reefs.”
His final report does not shy away from this conclusion. Garnaut (2008b: 127) concluded that stabilisation at 550 ppm CO2-e will result in:
“Disappearance of reef as we know it, with high impact to reef-based tourism. Three-dimensional structure of the corals largely gone and system dominated by fleshy seaweed and soft corals.”
“A carbon dioxide concentration of 500 ppm or beyond, and likely associated temperature change, would be catastrophic for the majority of coral reefs across the planet. Under these conditions the three-dimensional structure of the Great Barrier Reef would be expected to deteriorate and would no longer be dominated by corals or many of the organisms that we recognise today.”
The White Paper all but dismisses “stabilising concentrations of greenhouse gases at around 450 parts per million or lower” because “achieving global commitment to emissions reductions of this order appears unlikely in the next commitment period [after the commitment period for the Kyoto Protocol ends in 2012].”
Note, there are significant differences in targets based on stabilising atmospheric carbon dioxide at 500 ppm (which picture C above depicts) and stabilising total radiative forcing of greenhouse gases and aerosols at 500 ppm CO2-e (see Avoiding confusion on stabilization targets for climate change and ocean acidification).
However, the White Paper appears to assume total radiative forcing will continue to roughly equal atmospheric carbon dioxide levels. Therefore, by aiming to stabilise atmospheric greenhouse gases at around 510 to 550 ppm CO2-e, the White Paper appears to be aiming to stabilise atmospheric carbon dioxide (currently around 385 ppm) at these levels.
This should sound alarm bells for anyone following the scientific literature on ocean acidification, which has found serious impacts occur to coral reefs and much of the marine ecosystem above 450-500 ppm carbon dioxide in the atmosphere (Hoegh-Guldberg et al 2007; Cao and Caldeira 2008).
The public debate in Australia has largely ignored these impacts and it remains to be seen whether there will be any real challenge to the current approach being taken by the Australian Government.
The government has been less than frank on the implications of the targets it has chosen. There is no acknowledgment of the expected impacts to the Great Barrier Reef of stabilising at 510 – 550 ppm carbon dioxide or CO2-e and the choice of stabilising in this range is obscurely buried in the body of this 800 page report.
The White Paper refers repeatedly to 2020 targets of 5-15% reductions. It also refers repeatedly to stabilising at or below 450 ppm, with Garnaut’s pessimistic conclusion that “achieving global commitment to emissions reductions of this order appears unlikely”. But a reader must connect the 5-15% reductions to one of six scenarios set out on page 4-11 of the White Paper to uncover the overall stabilisation goals.
The White Paper relies heavily on Garnaut’s findings but a reader must also connect the obscurely buried stabilisation range of 510-550 ppm in the White Paper to Garnaut’s findings in his 600 page final report.
The government appears to be silently ignoring the expected impacts to the Great Barrier Reef and seeking to avoid confrontation on these implications in selling its climate change policies to the public. Tony Jones repeatedly asked Climate Minister Penny Wong of the implications for the Great Barrier Reef of stabilising at 550 ppm in an interview on ABC Lateline on (30 November 2008). She obviously knew the answer but danced around the questions to avoid stating that the government’s targets would mean the destruction of the Great Barrier Reef.
Perhaps it is too late to save the Great Barrier Reef but silently ignoring the expected impacts when setting climate change targets is disingenuous and does not advance the public debate. We need to fully acknowledge what the science is telling us. Choosing not to listen to weather forecasts does not stop it raining.
We should judge our climate change policies by this simple test: will we leave the GBR for our children? At present the answer we are giving to this question is “no”. We are all responsible for changing the answer to “yes”.
We should demand targets based on what we as a society want to achieve. We should not accept targets that will produce unacceptable outcomes.
- Australian Government (2008), Carbon Pollution Reduction Scheme – Australia’s Low Pollution Future – White Paper (Department of Climate Change, Canberra, 2008), available at http://www.climatechange.gov.au/whitepaper/index.html
- Cao L and Caldeira K (2008) “Atmospheric CO2 stabilization and ocean acidification” Geophys. Res. Lett., 35, L19609, doi:10.1029/2008GL035072.
- Garnaut R (2008a), Garnaut Review Supplementary Draft Report: Targets and trajectories (Garnaut Review, Canberra, 5 September 2008), p 38, available at http://www.garnautreview.org.au/CA25734E0016A131/pages/all-reports–resources.
- Garnaut R (2008b), Garnaut Climate Change Review Final Report (Cambridge University Press), http://www.garnautreview.org.au/index.htm.
- Hoegh-Guldberg O, et al (2007) “Coral Reefs Under Rapid Climate Change and Ocean Acidification” Science 318, 1737, DOI: 10.1126/science.1152509
- Lateline (30 November 2008), available at http://www.abc.net.au/lateline/content/2008/s2406044.htm
The Courier Mail has a similar analysis of the implications of the targets in the CPRS White Paper, “Australia’s carbon reduction target has ‘condemned Great Barrier Reef to death”, at http://www.news.com.au/story/0,27574,24806982-421,00.html
Richard Denniss also has an insightful op-ed in The Age laced with black humour at http://www.theage.com.au/opinion/households-pay-as-big-polluters-cash-in-on-climate-change-20081216-6zrp.html?page=-1
Anna Rose has a good, short analysis of the Carbon Polluters Rescue Scheme in New Matilda at http://newmatilda.com/2008/12/16/rudds-emission-target-policy-analysis
There is absolutely no doubt that swift action is needed to reduce CO2 emissions in order to avoid disastrous consequences on the Earth system, both regarding climate and ocean acidification. However, I would like to stress that this post does not accurately describe the present knowledge on the consequences of ocean acidification on coral reefs.
There is ample evidence that elevated pCO2 hampers calcification of reef organisms and favors dissolution of calcium carbonate. Additionally, the combined effect of elevated pCO2 and temperature triggers bleaching. These effects jeopardize the very existence of coral reefs. However, I contend that no one knows how a coral reef will look like at future levels of pCO2 and that no specific threshold or tipping point has been reported so far.
The photographs shown in figure 5 of the paper by Hoegh-Guldberg et al. (2007) have been used before on this blog. It must be emphasized that this paper did not report on experimental or field-based observations on the combined impacts of elevated pCO2 and temperature. Therefore these photographs are not based on actual research or experiments. In fact, there have probably been shot in sites bathed by waters with pCO2 values similar in each site and lower than the 510 to 550 ppm target discussed in the blog post. The photographs just reflect the authors’ perception on how coral reefs will look like at different pCO2 levels (the legend reads “Extant examples of reefs from the Great Barrier Reef that are used as analogs for the ecological structures we anticipate for Coral Reef Scenarios CRS-A, CRS-B, and CRS-C (see text). The [CO2]atm and temperature increases shown are those for the scenarios and do not refer to the locations photographed….”).
The paper by Cao and Caldeira (2008) cited in the blog post does not discuss impacts. It reports on the surface area of coral reefs that will be in waters with a carbonate chemistry similar to that of pre-industrial time. They demonstrate that “at a stabilization level of 550 ppm, there will be no water left in the open ocean with the kind of chemistry (aragonite saturation levels) experienced by more than 98% of shallow-water coral reefs before the advent of the industrial revolution”. That is a very striking change but the autors do not address impacts.
In closing, the point of this comment is not to dismiss the need for reducing CO2 emissions to avoid dire consequences on coral reefs and other ecosystems. I just want to point out that, to the best of my knowledge, only one threshold value is currently available. The German Advisory Council on Global Change (Schubert et al., 2006) proposed the following “guard rail”: “the pH value of near surface waters should not drop more than 0.2 units below the pre-industrial average value of 8.18 in any larger ocean region (nor in the global mean)”. This threshold, which is based on extremely limited information, will hopefully be refined soon as a result of the current active research in the field of the impacts of ocean acidification.
Cao L. & Caldeira K., 2008. Atmospheric CO2 stabilization and ocean acidification. Geophysical Research Letters 35, L19609.
Hoegh-Guldberg O., Mumby P. J., Hooten A. J., Steneck R. S., Greenfield P., Gomez E., Harvell C. D., Sale P. F., Edwards A. J., Caldeira K., Knowlton N., Eakin C. M., Iglesias-Prieto R., Muthiga N., Bradbury R. H., Dubi A. & Hatziolos M. E., 2007. Coral reefs under rapid climate change and ocean acidification. Science 318:1737-1742.
Schubert R., Schellnhuber H.-J., Buchmann N., Epiney A., Grießhammer R., Kulessa M., Messner D., Rahmstorf S. & Schmid J, 2006. The future of oceans- Warming up, rising high, turning sour. 110 p. Berlin: German Advisory Council on Global Change.
To the extent that Heogh-Guldberg et al (2007), Cal and Caldeira (2008), and Garnaut (2008) accurately reflect the wider literature on ocean acidification, this post does accurately describe the present knowledge on the consequences of ocean acidification on coral reefs.
The main point of this post was not to review the literature on ocean acidification but to highlight that the Australian Government’s emission reduction targets were aiming for levels that the main study upon which the targets were based (the Garnaut report) concluded would effectively destroy the Great Barrier Reef.
Professor Garnaut is an economist and his conclusions on the science must be treated with caution but the White Paper did not dispute his conclusions on the effect of stabilising at different levels. To the extent that the White Paper is based on his report, it must accept the assumptions Garnaut made and the conclusions he reached.
Garnaut’s report was based on a number of reports commissioned by him, including one on the effects of climate change on the GBR by Ove Heogh-Guldberg.
You are right that Heogh-Guldberg et al (2007) was a review article and did not, therefore, report experimental results. Cao and Caldeira (2008) was also a simulation.
You are also correct that no one knows for certain how a coral reef will look like at future levels of pCO2, but based on what we know at present, Heogh-Guldberg et al (2007) and Cao and Caldeira (2008) postulate that 450-500 ppm CO2 in the atmosphere will have serious delerious effects on coral reefs. Those are specific thresholds and tipping points.
It seems that you missed my point. None of the references mentioned in your post describe the biological impacts that will occur when pCO2 will reach 510 to 550 ppm. I am not familiar with the Garnaut report and this comment only concerns articles published in scientific journals.
I still contend that no one knows how a coral reef will look like at future levels of pCO2 and that no specific threshold or tipping point has been reported in the scientific literature so far.
Jean-Pierre: i don’t understand the motive of your comments. what exactly is the point you are trying to get across?
in your first post you tell us that “The photographs shown in figure 5 of the paper by Hoegh-Guldberg et al. (2007) have been used before on this blog. It must be emphasized that this paper did not report on experimental or field-based observations on the combined impacts of elevated pCO2 and temperature. therefore these photographs are not based on actual research or experiments.” this is in itself obvious, as at the time there were no experimental observations, and as this deals with future projected levels, it’s not surprising that there are no field-based observations. in the hoegh-guldberg paper, the figure to hand is labelled ‘extent examples’. do you feel these suggestions are unreasonable?
“There is ample evidence that elevated pCO2 hampers calcification of reef organisms and favors dissolution of calcium carbonate. Additionally, the combined effect of elevated pCO2 and temperature triggers bleaching. These effects jeopardize the very existence of coral reefs. However, I contend that no one knows how a coral reef will look like at future levels of pCO2 and that no specific threshold or tipping point has been reported so far.”
this statement seems like a very odd contradiction.
‘None of the references mentioned in your post describe the biological impacts that will occur when pCO2 will reach 510 to 550 ppm.”
clearly more research is required to determine exact tipping points, but if you believe that ample pco2 affects reefs, why are you so adverse to reccomendations of constraining atmospheric co2 levels?
Pingback: Climate Shifts » Uncategorized » Declining calcification on the Great Barrier Reef
Hi Jean-Pierre, have you seen this recent paper? McNeil & Matayar (2008) Southern Ocean acidification: A tipping point at 450-ppm atmospheric CO2. Proceedings of the National Academy of Sciences 105 18860-18864
Southern Ocean acidification via anthropogenic CO2 uptake is expected to be detrimental to multiple calcifying plankton species by lowering the concentration of carbonate ion (CO32-) to levels where calcium carbonate (both aragonite and calcite) shells begin to dissolve. Natural seasonal variations in carbonate ion concentrations could either hasten or dampen the future onset of this undersaturation of calcium carbonate. We present a large-scale Southern Ocean observational analysis that examines the seasonal magnitude and variability of CO32- and pH. Our analysis shows an intense wintertime minimum in CO32- south of the Antarctic Polar Front and when combined with anthropogenic CO2 uptake is likely to induce aragonite undersaturation when atmospheric CO2 levels reach approximate to 450 ppm. Under the IPCC IS92a scenario, Southern Ocean wintertime aragonite undersaturation is projected to occur by the year 2030 and no later than 2038. Some prominent calcifying plankton, in particular the Pteropod species Limacina helicina, have important veliger larval development during winter and will have to experience detrimental carbonate conditions much earlier than previously thought, with possible deleterious flow-on impacts for the wider Southern Ocean marine ecosystem. Our results highlight the critical importance of understanding seasonal carbon dynamics within all calcifying marine ecosystems such as continental shelves and coral reefs, because natural variability may potentially hasten the onset of future ocean acidification.
I have re-read the post and your comments and, with the greatest of respect to your expertise and publications in this field, I do not see that your comments are substantiated.
Hoegh-Guldberg et al (2007) discussed the literature on impacts to coral calcification and growth rates of different pCO2 at pages 1737-1738, including the results of both manipulative and field experiments. They discussed coral reef resilience and tipping points at pages 1738-1739. This is the basis for their subsequent discussion of the expected impacts of rising atmospheric CO2.
Hoegh-Guldberg et al (2007) suggest at page 1740 that “reef erosion will exceed calcification at [CO2]atm = 450 to 500 ppm … [At these levels the] density and diversity of corals on reefs are likely to decline, leading to vastly reduced habitat complexity and loss of biodiversity, including losses of coral associated fish and invertebrates.”
Hoegh-Guldberg et al (2007) suggest at pages 1740-1741 that “Increases in [CO2]atm > 500 ppm will … will reduce coral reef ecosystems to crumbling frameworks with few calcareous corals.”
I, therefore, consider that your comments that “none of the references mentioned in your post describe the biological impacts that will occur when pCO2 will reach 510 to 550 ppm” and “no specific threshold or tipping point has been reported in the scientific literature so far” are not substantiated. You may disagree with Heogh-Guldberg et al (2007) but they did describe the biological impacts they expect to occur when pCO2 reaches over 450-500 ppm, which they suggest is a specific threshold or tipping point, and their article is part of the scientific literature.
I conclude by noting that I respect greatly your expertise on the topic of ocean acidification and your publications on this topic over many years, helpfully listed at http://www.obs-vlfr.fr/~gattuso/jpg_papers_list.php