The Center for the Study of Carbon Dioxide and Global Change in Tempe, Arizona, has just issued a major report that compares projections from climate models to real world observations.

The report deals with the following climate model claims: “(1) unprecedented warming of the planet, (2) more frequent and severe floods and droughts, (3) more numerous and stronger hurricanes, (4) dangerous sea level rise, (5) more frequent and severe storms, (6) increased human mortality, (7) widespread plant and animal extinctions, (8) declining vegetative productivity, (9) deadly coral bleaching, and (10) a decimation of the planet’s marine life due to ocean acidification. And in conjunction with these analyses, we proffer our view of what the future may hold with respect to the climatic and biological consequences of the ongoing rise in the air’s CO2 content, concluding by providing an assessment of what we feel should be done about the situation.”

The 168-page report (2.5Mb) may be downloaded here.

“Real-world observations fail to confirm essentially all of the alarming predictions of significant increases in the frequency and severity of droughts, floods and hurricanes that climate models suggest should occur in response to a global warming of the magnitude that was experienced by the earth over the past two centuries as it gradually recovered from the much-lower-than-present temperatures characteristic of the depths of the Little Ice Age. And other observations have shown that the rising atmospheric CO2 concentrations associated with the development of the Industrial Revolution have actually been good for the planet, as they have significantly enhanced the plant productivity and vegetative water use efficiency of earth’s natural and agro-ecosystems, leading to a significant “greening of the earth.”

Coral bleaching is caused by high sea temperatures, high solar irradiance, by anomalously low sea temperatures, and by sudden drops in temperature that accompany intense upwelling episodes, thermocline shoaling, or seasonal cold-air outbreaks.(1)

Many coral species have endured three periods of global warming, from the Pliocene optimum (4.3-3.3 million years ago) through the Eemian interglacial (125,000 years ago) and the mid-Holocene Optimum (6000-5000 years ago), when atmospheric CO₂ concentrations and sea temperatures often exceeded those of today. Data show that an increase in sea warming of less than 2°C would result in a greatly increased diversity of corals in certain high latitude locations.(1)

Some coral bleaching may be due to marine pathogens, i.e., diseases.(2) Coral polyps depend on symbionts such as zooxanthellae (algal symbionts). These symbionts vary seasonally and with environmental stress. (3) Some symbionts are highly adaptable, and some corals can change their symbionts to better suit conditions. (14)

Some coral bleaching appears to be synchronous with El Nino events which raise water temperature. (4)

Although corals may endure bleaching, they are resilient. For instance, scleractinian corals, which are the major builders of the reefs of today, first appeared during mid-Triassic time 210 million years ago, when the earth was considerably warmer. They endured the Cretaceous Period, when temperatures were as much as 10-15°C higher than now. And they survived the warm and cold cycles of Pleistocene glacial epochs. (5,6,7)

One of the reasons coral are resilient and able to withstand a wide range of temperature, salinity, and CO₂ variations is that they shuffle symbionts. (8,9,10) For instance, “as the community structure of coral reefs shift in response to global climate change and water quality impacts, opportunistic corals harboring symbionts that enable maximum rates of growth may similarly gain a competitive advantage.” (13) The corals themselves also have several mechanisms to deal with and deflect thermal stress, including dynamic photo-protective mechanisms, and the expression of heat-shock proteins.

On the issue of coral calcification, observation finds that the combination of increased CO₂ (which provides more carbonate) and the shuffling of symbionts, makes the corals able to withstand the variations of temperature, disease, and solar irradiation. (11,12)

Real world observations trump the scare stories derived from theoretical models.

While human CO₂ emissions have little effect on coral health, we are, however, significantly affecting corals in other ways through runoff and nutrient enrichment; coastal construction leading to smothering of habitat and creation of high turbidity around coasts; and over fishing. Local management of water quality would seem to be the best thing we can do to aid corals.

See a summary of studies of human impact here: http://www.co2science.org/articles/V12/N41/EDIT.php

Sources:

1. Glynn, P.W. 1996. Coral reef bleaching: facts, hypotheses and implications. Global Change Biology 2: 495-509

2. Hayes, R.L. and Goreau, N.I. 1998. The significance of emerging diseases in the tropical coral reef ecosystem. Revista de Biologia Tropical 46 Supl. 5: 173-185

3. Fagoonee, I., Wilson, H.B., Hassell, M.P. and Turner, J.R. 1999. The dynamics of zooxanthellae populations: A long-term study in the field. Science 283: 843-845.

4. Stone, L., Huppert, A., Rajagopalan, B., Bhasin, H. and Loya, Y. 1999. Mass coral reef bleachng: A recent outcome of increased El Niño Activity? Ecology Letters 2: 325-330

5. Wells, J.W. 1956. Scleractinia. In: Moore, R.C., Ed. Treatise on Invertebrate Paleontology, Volume F, Coelenterata. Geological Society of America and University of Kansas Press, Lawrence, KS, pp. 353-367.

6. Chadwick-Furman, N.E. 1996. Reef coral diversity and global change. Global Change Biology 2: 559-568

7. Pandolfi, J.M. 1999. Response of Pleistocene coral reefs to environmental change over long temporal scales. American Zoologist 39: 113-130

8. Adjeroud, M., Augustin, D., Galzin, R. and Salvat, B. 2002. Natural disturbances and interannual variability of coral reef communities on the outer slope of Tiahura (Moorea, French Polynesia): 1991 to 1997. Marine Ecology Progress Series 237: 121-131.

9. Apprill, A.M. and Gates, R.D. 2007. Recognizing diversity in coral symbiotic dinoflagellate communities. Molecular Ecology 16: 1127-1134.

10. Baird, A.H., Cumbo, V.R., Leggat, W. and Rodriguez-Lanetty, M. 2007. Fidelity and flexibility in coral symbioses. Marine Ecology Progress Series 347: 307-309.

11. Bessat, F. and Buigues, D. 2001. Two centuries of variation in coral growth in a massive Porites colony from Moorea (French Polynesia): a response of ocean-atmosphere variability from south central Pacific. Palaeogeography, Palaeoclimatology, Palaeoecology 175: 381-392

12. Buddemeier, R.W. 1994. Symbiosis, calcification, and environmental interactions. Bulletin Institut Oceanographique, Monaco 13: 119-131

13. Cantin, N.E., van Oppen, M.J.H., Willis, B.L., Mieog, J.C. and Negri, A.P. 2009. Juvenile corals can acquire more carbon from high-performance algal symbionts. Coral Reefs 28: 405-414.

14. Fitt, W.K., et al., 2009, Response of two species of Indo-Pacific corals, Porites cylindrica and Stylophora pistillata, to short-term thermal stress: The host does matter in determining the tolerance of corals to bleaching. Journal of Experimental Marine Biology and Ecology 373: 102-110.