Coral reefs
From ClimateWiki
From Climate Change Reconsidered, a work of the Nongovernmental International Panel on Climate Change
According to the IPCC, “many studies incontrovertibly link coral bleaching to warmer sea surface temperature … and mass bleaching and coral mortality often results beyond key temperature thresholds” (IPCC 2007-II, p. 235). “Modelling,” the IPCC goes on to say, “predicts a phase switch to algal dominance on the Great Barrier Reef and Caribbean reefs in 2030 to 2050.” The IPCC further claims that “coral reefs will also be affected by rising atmospheric CO2 concentrations … resulting in declining calcification” (Ibid.).
In the following pages we review the scientific literature on coral reefs in an effort to determine if the ongoing rise in the air’s CO2 content, rising temperatures, or rising sea levels pose a threat to these incomparable underwater ecosystems. Because the fate of the earth’s corals has become so prominent in the debate over climate change and because our findings are so entirely at odds with those of the IPCC, we present a brief summary of our key findings here:
-There is no simple linkage between high temperatures and coral bleaching.
-As living entities, corals are not only acted upon by the various elements of their environment, they also react or respond to them. And when changes in environmental factors pose a challenge to their continued existence, they sometimes take major defensive or adaptive actions to ensure their survival.
-A particularly ingenious way coral respond to environmental stress is to replace the zooxanthellae expelled by the coral host during a stress-induced bleaching episode by one or more varieties of zooxanthellae that are more tolerant of the stress that caused the bleaching.
-The persistence of coral reefs through geologic time—when temperatures were as much as 10°-15°C warmer than at present, and atmospheric CO2 concentrations were two to seven times higher than they are currently—provides substantive evidence that these marine entities can successfully adapt to a dramatically changing global environment.
-Thus, the recent die-off of many corals cannot be due solely, or even mostly, to global warming or the modest rise in atmospheric CO2 concentration over the course of the Industrial Revolution.
-The 18- to 59-cm warming-induced sea-level rise that is predicted for the coming century by the IPCC—which could be greatly exaggerated if predictions of CO2-induced global warming are wrong—falls well within the range (2 to 6 mm per year) of typical coral vertical extension rates, which exhibited a modal value of 7 to 8 mm per year during the Holocene and can be more than double that value in certain branching corals. Rising sea levels should therefore present no difficulties for coral reefs. In fact, rising sea levels may have a positive effect on reefs, permitting increased coral growth in areas that have already reached the upward limit imposed by current sea levels.
-The rising CO2 content of the atmosphere may induce changes in ocean chemistry (pH) that could slightly reduce coral calcification rates; but potential positive effects of hydrospheric CO2 enrichment may more than compensate for this modest negative phenomenon.
-Theoretical predictions indicate that coral calcification rates should decline as a result of increasing atmospheric CO2 concentrations by as much as 40 percent by 2100. However, real-world observations indicate that elevated CO2 and elevated temperatures are having the opposite effect.
References
Climate Change Reconsidered: Website of the Nongovernmental International Panel on Climate Change. http://www.nipccreport.org/archive/archive.html
IPCC, 2007-II. 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, UK.
Related Links
Widespread coral bleaching events
Coral reefs and sea level rise
Coral reefs and ocean acidification
