No, if we take action now against climate change and other activities harming the Reef, we can still protect it from further damage. But CO2 emissions must stop increasing within the next few years and start decreasing to ensure the Reef is secured for future generations.
The best science has shown that coral reefs are in grave danger if atmospheric carbon dioxide concentrations exceed 450ppm (Hoegh-Guldberg et al, 2007). This is also the case for the wet tropics, Kakadu and many other precious ecosystems - which will also disappear. Of similar importance, is the observation that the expected 2°C rise in global temperature will set in motion the melting of the ice sheets associated with Greenland and Antarctica. The sudden and dramatic loss of Arctic sea ice is the expected precursor to the breakdown of the Greenland Ice Sheet. These changes will drive sea level rise in the order of 5 m this century and may eventually result in 50 m sea level rises over the next 300 years. This would be catastrophic for both the Reef and the planet and must be avoided.
back to top
- One of the most diverse and biologically complex marine ecosystems in the world
- 10% of world fish species
- Contributes $5.8 billion annually to the Australian economy
- Generates about 63,000 jobs
- 1.9 million visitations to the Reef each year
- Its diversity represents a valuable storehouse of new technologies for industry and medicine (e.g. cone shell toxin)
- World Heritage listed and one of the seven natural wonders of the world. Australia has committed to an obligation to look after the Reef for the world.
back to top
Some areas of the Reef have been sheltered from the impacts of human activities and climate change (e.g. located in areas flushed with cool oceanic waters, protected from recreational and commercial fishing, not directly impacted by river runoff) and may not have shown any significant signs of deterioration. However, this doesn’t mean that the Reef is not being damaged or is not under threat. Deterioration of the Reef is manifested over many years, and signs may not be immediately visible to the untrained eye or even regular Reef visitors. Research has clearly demonstrated that the Reef is being damaged (GBRMPA, 2009). In addition, long term monitoring programs such as that run by the Australian Institute of Marine Science have recorded the deterioration of the Reef over many years (e.g. changes in fish communities, increases in Crown of Thorns starfish, increases in algae).
The observations of a single individual (e.g. the diving enthusiasts Walter A. Stark and Ben Cropp are often mentioned) do not match up to the systematic study of the Reef over hundreds of sites and multiple decades by numerous scientists trained in ecology. While having a PhD, Walter A. Stark’s main expertise lies in fish taxonomy not marine ecology.
back to top
There are two major threats posed by climate change which will have significant impacts for the Reef:
Increase in ocean temperature
There are over 400 species of corals on the Reef. Together, they provide the foundations of the greater structure of the Reef. Living within these corals are microscopic organisms called zooxanthellae that nourish the coral host through photosynthesis and give reef building corals both life and colour. They are the life-blood of a healthy coral reef.
However, corals and their zooxanthellae live in delicate balance with their environment. Even the smallest changes in temperature can cause the zooxanthellae to be expelled from the coral, leaving the coral skeletons looking white or bleached (coral bleaching). Unless conditions return to normal, usually within 4-6 weeks, the coral will get diseased or die. In 1998, 60% of the Great Barrier Reef bleached, and about 5-10% of the reef died.
Under so-called natural circumstances, coral reefs can recover from disturbances such as Crown of Thorns Starfish outbreaks. The problem is the recovery from the impacts of events like coral bleaching, which did not occur to any real extent prior to 1979. Reefs are devastated by these events and may take up to 20 years to recover - if coral bleaching events continue to become more frequent, and reefs did not have time to recover in between bleaching events, then coral reefs will eventually lose the corals that build and maintain them.
There is variability among different coral species with respect to thermal stress. The soft and fragile branching corals are among the first to bleach while the massive corals are able to survive another 1-2oC before bleaching. The projected scenarios of climate change, therefore, will result in different yet less diverse reef communities in the short-term. If sea temperatures continue to rise, however, these changed reef communities will disappear.
Bleaching not only significantly impacts our coral populations.Corals build the three-dimensional structure of reefs, which is essential for the habitats of fish and several hundred thousand other species. It also endangers many other organisms in larger reef ecosystems; invertebrates like starfish and anemones, fish, turtles and sea birds all depend on the corals for food and protection. On a larger scale, entire industries and communities rely on healthy reef systems to sustain them; the Reef alone is, even on the most conservative of measures, said to have a total assessed value of $51.4 billion (Oxford Economics, 2009).
Ocean acidification
Increasing carbon dioxide concentrations in the atmosphere leads to more carbon dioxide being absorbed into the ocean. When in the ocean, carbon dioxide reacts with water to create a dilute acid (carbonic acid), which lowers the pH and decreases the concentration of the ion, carbonate, which is crucial for the construction of the limestone-like calcium carbonate skeletons of corals. A recent paper from the Australian Institute of Marine Sciences (De’Ath et al, 2009) has shown that the ability of corals to form their skeletons is now 15% less than what it was prior to 1990. Another paper by scientists from University of Queensland (Anthony et al, 2008) has shown that temperature and acidity interact to have a much greater impact on corals than either impact has on its own. This means that the currently small temperature thresholds of corals are likely to be reduced even further with an acidifying ocean and will therefore bleach more readily.
All the evidence suggests that increasing carbon dioxide levels in the atmosphere above 450 ppm will lead to carbonate ion concentrations which will be unable to support the formation and maintenance of coral reefs. In a nutshell, more carbon dioxide, greater acidification of the ocean, less carbonate ions and less calcification by corals. Above 450 ppm carbon dioxide in the atmosphere, carbonate reefs no longer exist.
These direct effects of climate change will combine with more localised stresses to further degrade coral reef ecosystems. Although climate change itself will adversely affect coral reefs, it will also increase the susceptibility of reefs to degradation and loss resulting from increased frequency and severity of cyclones and storms as well as disease, over-fishing, and pollution from neighboring human communities.
back to top
Corals have adapted to changes in their environment, with corals growing across the globe in a range of different thermal environments. The problems of using these geographical differences as evidence that coral populations can evolve to keep pace with climate change, however, is that the rate at which these evolutionary changes has occurred is likely to be very long. The current rates of environmental change are 100 to 1000 times faster than even the fastest rate of change in the environment over the past million years at least.
Evolution, which is the process by which corals have adapted in the past to much lower rates of environmental change, takes time. Corals have long generation times (3-100 years) and evidence that evolution can keep up with the rate of climate change is lacking (Hoegh-Guldberg, 2009).
There are a growing number of studies that have shown that corals can improve their thermal tolerance slightly on a short term basis in response to small increases in temperature. These changes, however, are not long term and not a continuing solution for corals in the face of climate change. Corals also have a fairly inflexible relationship with zooxanthellae which does not allow them to quickly adapt to changes in temperature. All of the evidence suggests that a coral’s ability to adapt genetically to the current rates of change has not occurred.
back to top
The migration of corals southward is dependent on the distance that corals generations are able to disperse, i.e. how far can a coral larvae travel southward from its parents. Recent evidence suggests that this dispersal distance is in the order of 5-100km (Underwood et al 2007). Latitudinal gradients in temperature are in the vicinity of 1.5oC per thousand kilometres, suggesting coral larvae will need to travel over 20km each year to keep pace with a 3oC temperature rise over the next 100 years. Thermal stress also impacts the reproductive output of corals which means less coral larvae will survive a large trip southward. So the migration of corals southward at rates to keep up with the projects changes in temperature become unlikely. In addition, several studies has shown a decrease in carbonate ion concentrations at higher latitudes making southward migration more difficult.
back to top
Restricting the analysis of the data to the past eight years is like looking at the last ten minutes of the Dow Jones and claiming we are not in a financial crisis. While the average global temperature has not increased in the past eight years, they have been eight of the hottest years on record. We must look at the bigger picture and it is telling us that since the 1950’s, the average global temperature has increased at an alarming rate. While the earth has experienced hotter periods, they have occurred over tens of thousands of years. By contrast, the rate of change we are seeing today has occurred in less than 50 years.
The selective reporting of only part of a dataset is a common tactic by climate change deniers.
back to top
The IPCC has four predictions based on various scenarios of economic growth and globalisation (IPCC, 2007). The worst case scenario outlines what will happen if nothing is done, by 2100:
- average global temperatures will increase up to 6.4oC
- sea temperature will rise by 30-60 cm
- atmospheric CO2 levels will be above 500ppm
The consequences for the Reef are dire and we will see:
- increasing the acidity of the ocean
- coral reefs deteriorating to a crumbling framework with very few reef building corals
- erosion becoming a serious concern for coastal communities
- a weakened Reef being further compromised by the increased frequency and severity of cyclones and storms
- serious consequences for all organisms which depend upon it, including humans.
It is very important to understand that the scientific community now considers the estimates of the IPCC Fourth Assessment Report as being out of date and very conservative. The IPCC process demands consensus which makes it inherently conservative. Since the 2007 Fourth Assessment Report, we have already seen a massive loss of summer Arctic ice (50%) which is well beyond the worst case IPCC scenarios. This plus the evidence that appeared in the prestigious journals of Science and Nature of Greenland and Antarctic ice sheet breakdown, is suggesting that we have got the rate of climate change horribly wrong. This has serious implications for coastal ecosystems like the Great Barrier Reef because it suggests that sea level rise and temperatures may change sooner and more than expected. The implications and our response to this is self-evident and suggest that we must radically change course.
back to top
|
Year (scenario)
|
Atmospheric CO2 (ppm) concentration |
Temp changes (oC) of up to |
Reef impacts |
| Pre-industrial (baseline) |
260 |
|
|
| 2009 (maintaining current CO2 concentrations) |
380 |
+0.74 |
- Coral reefs will continue to change but will remain coral dominated
- Decreased coral growth and skeletal density
|
| 2100 (IPCC scenario of no action taken) |
800 |
+6.4 |
- Nonexistent reef growth
- Drowned reefs as sea levels rise
- Half or more of coral-associated fauna becoming rare or extinct
- Macroalgae/phytoplankton will dominate
|
| 2100 (Australian Government target of 5% reduction in emissions from 2000 levels) |
550 |
+3 |
- Decreases coral calcification and growth by up to 40%
- Rapid contraction of coral reefs and reduce reef ecosystems to crumbling frameworks with few calcareous corals
- Loss of coral-associated fauna
|
| 2100 (Australian Government target of 15% reduction in emissions from 2000 levels) |
510 |
+2.6 |
- Density and diversity of corals likely to decline
- Reef erosion will surpass reef building processes
- Reduced habitat complexity and loss of biodiversity
- Reefs at greater risk from other factors (overfishing, declining water quality)
|
| 2100 (Garnaut recommendation of 25% reduction in emissions from 2000 levels) |
450 |
+2 |
- Thermally tolerant and rapidly growing corals dominate
- Reef erosion equal to Reef building processes
- Increasing frequency and severity of mass coral bleaching, disease and mortality
|
back to top
If Australia adopts a 5% reduction in greenhouse gas emissions relative to 2000 levels, atmospheric CO2 concentrations will stabilise at 550ppm with a 3oC increase in average global temperature by 2100. As per above, at this CO2 level, will mean the loss of the Reef as we know it.
This particular policy position if adopted globally will essentially mean the end of the Reef, and most other natural ecosystems. It will also put Australia's capital cities into crisis over water and will severely damage our ability to produce food. Most credible scientists are now questioning whether this position makes any sense at all.
back to top
The absolute limit to the concentration of carbon dioxide in the atmosphere under which there will be some semblance of reef ecosystem is 450 ppm. 450ppm is considered the threshold for reef building versus reef erosion processes with thermally tolerant and rapid growing coral species dominating. Coral reefs may persist at 450ppm, but they will be very brittle ecosystems requiring enormous management and care to persist.
There is a growing movement of scientists that feel we must aim to stabilise carbon dioxide concentrations at 400 ppm.
A model developed by the Garnaut Climate Change Review assumes a united global approach with all countries taking on emissions reduction obligations by 2013. Under this model, a 25% reduction in greenhouse gas emissions will see atmospheric CO2 concentrations peak at 500ppm and then stabilise at 450ppm with a 2oC temperature increase by 2100. Coral reefs will still be significantly affected at CO2 concentrations of 450ppm. A greenhouse gas emissions reduction scheme will need to aim above 25% in order to protect and maintain the GBR.
back to top
Other countries such as India and China have the ability to have a significant impact on global emissions should they choose to act. China has already demonstrated their desire to tackle climate change, and their political system allows for the rapid implementation of significant changes on a massive scale.
As a developed country with a (relatively) strong economy, Australia can join with other developed nations (European Union nations) in leading the way in reducing emissions. The US has also recently demonstrated significant steps to reducing greenhouse gas emissions. These nations and their participation in an emissions reduction scheme will greatly influence Australia’s participation and contribution.
The market for emissions reduction technologies is expanding rapidly and Australia can become a part of this market by adopting an ambitious target and driving the development of technology. A significant reduction in greenhouse gas emissions can only help with the climate change situation, and would set an influential example for other nations especially in the Asian region.
This is an issue of leadership. If wealthy countries such as Australia don't seize the moment, the opportunities and the ethical imperative, then why should any other country worldwide make changes to deal with this problem.
back to top
Assuming united global action in reducing emissions, annual global growth will slow by around 0.1% per year from 2010 to 2050, from 3.5% per year with no action to 3.3-3.4% growth per year. This suggests global economic mitigation costs are equivalent to delaying global growth by about one year.
The earlier Australia acts, the cheaper the cost of action. The longer the delay in action, the more damage to the Australian economy is at risk. Many of Australia's key industries will become substantially more competitive, such as forestry, gas and hydroelectric energy. The growth in these industries will far outweight the costs to energy intensive industries such as coal fired energy and aluminium refining.
The steady implementation of action now will reduce the immediate impacts on the economy and reduce the future sharper shock to the economy which will occur if not action is taken.
The science tells us that we are heading towards a global catastrophe in which we will have two move away from CO2 omitting energy sources. This will involve a major restructuring of energy generation and distribution, and will involve an enormous number of new technologies. If Australia doesn't get involved in the development of these new technologies now, then it will become a third-party player in an important and lucrative future.
back to top
Apart from climate change, the Reef faces threats from other human activities. The quality of water running off the land and onto the Reef is directly impacted by land based activities. Poor water quality running off from agricultural and highly developed areas is characterised by high levels of sediment and nutrients and may include a cocktail of other toxins and pollutants. Best practices for agriculture and development to reduce runoff of sediments, nutrients and pollutants from the land will greatly increase the water quality and help protect the Reef.
Overfishing is also a significant threat to the Reef, especially where a particular species or group of fish is targeted. Sustainable fishing practices with a strong scientific foundation must be adopted by all fishers, commercial and recreational, to protect the Reef.
Coastal development along Queensland’s coastline is exposing the Reef to an unprecedented range of new pressures. Poor planning can result in poor quality water running off onto the reef laden with sediment, nutrients and toxins. Properly planned, managed and maintained development can reduce the amount of dirty water reaching the Reef.
Large ships regularly transit the inner route of the Reef, bringing with them the threat of major oil and chemical spills. In addition, the impact of waste products generated by routine shipping activities and ballast water treatment and management continue to cause concern. Best practices for shipping activities will help reduce the risk of accidents and threats posed by ballast and ship waste.
back to top
Anthony KR, Kline DI, Diaz-Pulido G, Dove S, Hoegh-Guldberg O (2008). Ocean acidification causes bleaching and productivity loss in coral reef builders. Proc Natl Acad Sci USA 105:17442– 17446
De’ath G, Lough JM, Fabricius KE (2009). Declining coral calcification on the Great Barrier Reef. Science 323:116–119
GBRMPA (2009). Great Barrier Reef Outlook Report 2009. Great Barrier Reef Marine Park Authority.
Hoegh-Guldberg O, Mumby PJ, Hooten AJ, Steneck RS, Greenfield P, Gomez E, Harvell CD, Sale PF, Edwards AJ, Caldeira K, Knowlton N, Eakin CM, Iglesias-Prieto R, Muthiga N, Bradbury RH, Dubi A, Hatziolos ME (2007) Coral reefs under rapid climate change and ocean acidification. Science 318:1737–1742
Hoegh-Guldberg O (2009). Climate change and coral reefs: Trojan horse of false prophecy? A response to Maynard et al. (2008). Coral Reefs 28:569-575
IPCC (2007). Climate Change 2007: Synthesis Report. Contribution of Working Groups I, II and III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, Pachauri, R.K and Reisinger, A. (eds.)]. IPCC, Geneva, Switzerland, 104 pp.
Oxford Economics (2009). Valuing the Effects of a Great Barrier Reef Bleaching. Great Barrier Reef Foundation.
Underwood JN, Smith LD, Van Oppen MJ, Gilmour JP (2007). Multiple scales of genetic connectivity in a brooding coral on isolated reefs following catastrophic bleaching. Mol Ecol 16:771–784
back to top
Complied with the assistance of Professor Ove Hoegh-Guldberg
Australian Institute of Marine Science
Great Barrier Reef Marine Park Authority
Skeptical Science
Doom and Boom on a Resilient Reef
back to top