Global Warming Effects Around the World

Great Barrier Reef, Australia

Top Impact

Ecosystems (Salt water)

Other Impacts

Temperature (Ocean)

Oceans (Ocean chemistry)

Comparative photos showing healthy and bleached corals illustrate what rising ocean temperatures and increasing acidification might mean for Australia's Great Barrier Reef.

The Great Barrier Reef off the coast of Australia is home to more than 400 kinds of coral. Global warming poses two major threats to the reef: coral bleaching, caused by rising ocean temperatures, and ocean acidification, which—if it crosses a critical level—deprives corals of the ingredients they need to build shells and skeletons.1

Key Facts

Australia's Great Barrier Reef—the world's largest coral reef—is a unique marine ecosystem threatened by global warming. Damage to the reef could harm the region's biodiversity, tourism, and fisheries.

  • The reef has suffered eight mass coral bleaching events since 1979, triggered by unusually high water temperatures.2,14,15 If there is enough time between bleaching events, the coral can often recover. However, annual bleaching is expected by mid-century if our heat-trapping emissions continue at their current pace, thus leaving the reef vulnerable to diseases from which it may not recover.2,12,14,17,19
  • Ocean acidification expected to occur if atmospheric carbon dioxide surpasses 500 parts per million is likely to limit the capacity of the reef to recover from bleaching events, and to cope with other stresses.2
  • Scientists project a significant loss of biodiversity within a decade, and at worst a 95 percent decrease in the distribution of Great Barrier Reef species by late this century.2,26

Details

The Great Barrier Reef is the world's largest continuous reef system, extending more than 1,300 miles (2,100 kilometers) through the Coral Sea off northeastern Australia.2 The reef is home to more than 400 types of coral, as well as coral sponges, mollusks, rays, dolphins, and a diverse array of tropical fish, birds, and reptiles.3 The reef is a breeding ground for humpback whales and a habitat for endangered species, such as the dugong (sea cow) and the large green sea turtle.3

The Great Barrier Reef is one of the seven wonders of the natural world, and a United Nations World Heritage Site.3,4 It is also a huge tourist attraction—worth around U.S. $6.4 billion ($6.9 billion in Australian dollars) annually to the Australian economy.2,5,6

Climate change poses two major threats to the Great Barrier Reef. The first is rising ocean temperatures, which can cause coral bleaching. The second is ocean acidification, which—if it crosses a threshold value—dissolves the calcium carbonate that forms the coral reef, curbing its ability to grow.2

Corals are marine animals. Their spectacular coloration comes from symbiotic algae, which also nourish them.7 When corals are stressed by sustained increases in ocean temperature, they can lose their nourishing algae, exposing the coral's white carbonate mineral structure. Many coral species evolved to occupy a narrow temperature niche, so even small increases in water temperature can cause coral bleaching. If the stress continues, the corals die.7,8

Since 1950, global mean sea surface temperatures have risen roughly 1° F (0.6° C).9 The intensity and frequency of coral bleaching has increased significantly over the past 30 years, causing death or severe damage to one-third of the world's corals.10 Coral diseases are also spreading.7,11,12

On the Great Barrier Reef, sea temperatures have warmed by about 0.7° F (0.4° C) over the past century.2,13 Eight mass coral bleaching events have occurred since 1979, triggered by unusually high water temperatures.

Bleaching was most widespread and intense in 1998 and 2002—affecting up to half of the reefs that compose the Great Barrier Reef system.2,14,15 The 2002 bleaching was followed by local outbreaks of coral disease. Some sites have seen a 500 percent increase in disease over the past decade.2,16

What the Future Holds

Annual bleaching on the Great Barrier Reef is expected by 2030, if today's trends in global warming pollution and rising ocean temperatures continue.2,14,17,18 Under a medium-emissions scenario, annual bleaching is projected to occur by mid-century.2,14,17,18 Because recovery from a die-off caused by coral bleaching takes at least 10 years, scientists expect opportunistic and non-nourishing algae to take over the Great Barrier Reef by 2050.2,14,19

What's more, as atmospheric concentrations of carbon dioxide rise, the oceans absorb the CO2, and their acidity increases. Ocean acidification is likely to further limit the ability of the Great Barrier Reef to recover from bleaching, and its overall resiliency.2

Ocean acidification also endangers corals and other sea animals that need calcium carbonate to build shells or skeletons.7,20,21 If the oceans continue to acidify, scientists project that corals risk being less able to build shells and skeletons.7,22,23 Studies show that a doubling of atmospheric CO2 is likely to reduce coral calcification more than 30 percent. Even at lower concentrations of atmospheric CO2, reefs are now eroding faster than new corals can form.7,24

Loss of biodiversity is another expected impact of global warming on the Great Barrier Reef. As corals die off, the number of species that the reef can support declines, and local extinctions can occur.7,25 Scientists project a significant loss of biodiversity on the reef within a decade—and at worst case a 95 percent decrease in the distribution of Great Barrier Reef species by late this century.2,26

These changes in the Great Barrier Reef are projected to harm the local economy significantly, especially fishing and tourism.2 Strategies to reduce other stresses—such as poor water quality and overfishing—could help mitigate the impacts of climate change, and help corals survive.2

Credits

Endnotes

  1. Photograph (left) used by permission, Scott Pudwell. Photograph (right) used by permission, Leonard Low.
  2. Hennessy, K., B. Fitzharris, B.C. Bates, N. Harvey, S.M. Howden, L. Hughes, J. Salinger, and R. Warrick. 2007. Australia and New Zealand. In Climate change 2007: Impacts, adaptation and vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Edited by M.L. Parry, O.F. Canziani, J.P. Palutikof, P.J. van der Linden, and C.E. Hanson. Cambridge University Press, pp. 507-540.
  3. Greatbarrierreef.org. 2010. About the Great Barrier Reef. Online at http://www.greatbarrierreef.org/ about.php. Accessed May 2, 2010.
  4. United Nations Educational, Scientific and Cultural Organization (UNESCO). World Heritage Sites: Great Barrier Reef. Paris. Online at http://whc.unesco.org/ en/ list/154. Accessed May 2, 2010.
  5. Steffen, W., A.A. Burbidge, L. Hughes, R. Kitching, D. Lindenmayer, W. Musgrave, M. Stafford Smith, and P.A Werner. 2009. Australia's biodiversity and climate change. Collingwood, Australia: CSIRO Publishing.
  6. Access Economics. 2005. Measuring the economic and financial value of the Great Barrier Reef Marine Park. Townsville, Australia: Great Barrier Reef Marine Park Authority. Online at http://www.accesseconomics.com.au/ publicationsreports/ showreport.php?id=10 &searchfor=Economic%20Consulting &searchby=area. Accessed May 2, 2010.
  7. U.S. Global Change Research Program. 2009. Global climate change impacts in the United States. Edited by T.R. Karl, J.M. Melillo, and T.C. Peterson. Cambridge University Press.
  8. Donner, S.D., W.J. Skirving, C.M. Little, M. Oppenheimer, and O. Hoegh-Guldberg. 2005. Global assessment of coral bleaching and required rates of adaptation under climate change. Global Change Biology 11(12):2251-2265.
  9. Bindoff, N., J. Willebrand, V. Artale, A. Cazenave, J. Gregory, S. Gulev, K. Hanawa, C. LeQuéré, and co-authors. 2007. Observations: Oceanic climate change and sea level. In: Climate change 2007: The physical science basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Edited by S. Solomon, D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor, and H. L. Miller. Cambridge University Press, pp. 385-432.
  10. Fischlin, A., G.F. Midgley, J.T. Price, R. Leemans, B. Gopal, C. Turley, M.D.A. Rounsevell, O.P. Dube, J. Tarazona, A.A. Velichko, 2007: Ecosystems, their properties, goods, and services. Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, M.L. Parry, O.F. Canziani, J.P. Palutikof, P.J. van der Linden and C.E. Hanson, Eds., Cambridge University Press, Cambridge, 211-272.
  11. Janetos, A., L. Hansen, D. Inouye, B.P. Kelly, L. Meyerson, B. Peterson, and R. Shaw. 2008. Biodiversity. In: The effects of climate change on agriculture, land resources, water resources, and biodiversity in the United States. Edited by P. Backlund, A. Janetos, D. Schimel, J. Hatfield, K. Boote, P. Fay, L. Hahn, C. Izaurralde, B.A. Kimball, T. Mader, J. Morgan, D. Ort, W. Polley, A. Thomson, D. Wolfe, M.G. Ryan, S.R. Archer, R. Birdsey, C. Dahm, L. Heath, J. Hicke, D. Hollinger, T. Huxman, G. Okin, R. Oren, J. Randerson, W. Schlesinger, D. Lettenmaier, D. Major, L. Poff, S. Running, L. Hansen, D. Inouye, B.P. Kelly, L. Meyerson, B. Peterson, and R. Shaw. Synthesis and assessment product 4.3. Washington, DC: U.S. Department of Agriculture, pp. 151-181.
  12. Miller, J., Muler, E., Rogers, C., Waara, R., Atkinson, A., Whelan, K.R.T, Patterson, M., Witcher, B. 2009. Coral disease following massive bleaching in 2005 causes 60% declaine in coral cover on reefs in the US Virgin Islands. Coral Reefs (2009) 28:925-937 Online at: http://springerlink.com/ content/ t8474w3380q1814q/
  13. Lough, J.M. 2000. 1997-98: Unprecedented thermal stress to coral reefs? Geophysical Research Letters 27:3901-3904.
  14. Done, T., P. Whetton, R. Jones, R. Berkelmans, J. Lough, W. Skirving, and S. Wooldridge. 2003. Global climate change and coral bleaching on the Great Barrier Reef. Townsville, Australia: Department of Natural Resources and Mining, State of Queensland Greenhouse Taskforce. Online at http://www.longpaddock.qld.gov.au/ ClimateChanges/ pub/ CoralBleaching.pdf.
  15. Berkelmans, R., G. De'ath, S. Kininmonth, and W.J. Skirving. 2004. A comparison of the 1998 and 2002 coral bleaching events of the Great Barrier Reef: Spatial correlation, patterns and predictions. Coral Reefs 23:74-83.
  16. Willis, B.L., C.A. Page, and E.A. Dinsdale. 2004. Coral disease on the Great Barrier Reef. In: Coral health and disease. Edited by E. Rosenberg and Y. Loya. New York, NY: Springer, pp. 69-104.
  17. Wooldridge, S., T. Done, R. Berkelmans, R. Jones, and P. Marshall. 2005. Precursors for resilience in coral communities in a warming climate: A belief network approach. Marine Ecology Progress Series 295:157-169.
  18. The emissions scenarios referred to here are the high-emissions path known as A1FI and the medium-emissions path known as A1T from the Intergovernmental Panel on Climate Change.
  19. Hoegh-Guldberg, O. 1999. Climate change, coral bleaching and the future of the world's coral reefs. Marine Freshwater Resources 50:839-866.
  20. Clarke, L., J. Edmonds, H. Jacoby, H. Pitcher, J. Reilly, and R. Richels. 2007. Scenarios of greenhouse gas emissions and atmospheric concentrations. Synthesis and assessment product 2.1, sub-report 2.1A. Washington, DC: U.S. Department of Energy, Office of Biological and Environmental Research.
  21. Orr, J.C., V.J. Fabry, O. Aumont, L. Bopp, S.C. Doney, R.A. Feely, A. Gnanadesikan, N. Gruber, A. Ishida, F. Joos, R.M. Key, K. Lindsay, E. Maier-Reimer, R. Matear, P. Monfray, A. Mouchet, R.G. Najjar, G.-K. Plattner, K.B. Rodgers, C.L. Sabine, J.L. Sarmiento, R. Schlitzer, R.D. Slater, I.J. Totterdell, M.-F. Weirig, Y. Yamanaka, and A. Yool. 2005. Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms. Nature 437(7059):681-686.
  22. Feely, R.A., C.L. Sabine, J.M. Hernandez-Ayon, D. Ianson, and B. Hales. 2008. Evidence for upwelling of corrosive "acidified" water onto the continental shelf. Science 320(5882):1490-1492.
  23. Orr, J.C., V.J. Fabry, O. Aumont, L. Bopp, S.C. Doney, R.A. Feely, A. Gnanadesikan, N. Gruber, A. Ishida, F. Joos, R.M. Key, K. Lindsay, E. Maier-Reimer, R. Matear, P. Monfray, A. Mouchet, R.G. Najjar, G.-K. Plattner, K.B. Rodgers, C.L. Sabine, J.L. Sarmiento, R. Schlitzer, R.D. Slater, I.J. Totterdell, M.-F. Weirig, Y. Yamanaka, and A. Yool. 2005. Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms. Nature 437(7059):681-686.
  24. Royal Society of London. 2005. Ocean acidification due to increasing atmospheric carbon dioxide. Policy document 12/05. London.
  25. Graham, N.A.J., S.K. Wilson, S. Jennings, N.V.C. Polunin, J.P. Bijoux, and J. Robinson. 2006. Dynamic fragility of oceanic coral reef ecosystems. Proceedings of the National Academy of Sciences 103(22):8425-8429.
  26. Jones, R.J., J. Bowyer, O. Hoegh-Guldberg, and L.L. Blackall. 2004. Dynamics of a temperature-related coral disease outbreak. Marine Ecology Progress Series 281:63-77.
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