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.”

One of the global warming scare stories we hear is that increased carbon dioxide emissions cause ocean acidification and rising temperatures that contribute to coral bleaching or other harm to corals. I dealt with ocean acidification in a previous blog. The issue is complicated; here is what research says. (Note: numbers in parentheses after a sentence refer to a specific reference.)

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.

We often read in the media that increasing carbon dioxide in the atmosphere will make the oceans too acidic, and dissolve or otherwise harm carbonate-shelled marine fauna. These writers or reporters seem ignorant of the fact that these marine fauna evolved when the atmospheric CO₂ concentration was more than 10 times higher than the current level.(1) Ironically, a recent New York Times article was fretting that the ocean is not absorbing enough carbon dioxide to act as a good carbon “sink.”

The metric for acidity/alkalinity is called pH. The pH is defined as the negative logarithm of the hydrogen ion concentration (or the logarithm of 1 divided by the hydrogen ion concentration). The pH scale goes from zero to 14 with pH of 7 being neutral, lower than 7 is acidic, and higher than 7 alkaline.

Two factors control the amount of carbon dioxide in the ocean: ocean temperature and amount of carbon dioxide in the atmosphere, i.e., its partial pressure. Cooler oceans and higher atmospheric CO₂ should result in more carbon dioxide in the oceans.

Henry’s law states that the concentration of a gas in a liquid is proportional to the partial pressure of the gas in equilibrium above the liquid. It stands to reason that more CO₂ in the atmosphere would translate to more in the ocean. However, Henry’s law assumes constant temperature. If the temperature changes, then the absorption changes. If the oceans warm, CO₂ will leave the ocean and return to the atmosphere. Cold liquids can hold more dissolved gas than warm liquids. Just think of what happens to a carbonated beverage left to warm to room temperature.

It has been estimated that current ocean pH is 0.1 pH unit less alkaline than it was in recent pre-industrial time, and some climate models predict a further decrease of 0.7 pH units by 2300.(2) However, proxy reconstructions of ocean acidity, based on fossil and modern corals, show that ocean pH has oscillated between pH of 7.91 and 8.29 during the past seven thousand years.(3) That cyclic variation is nearly four times larger than the 0.1 decrease alarmists are whining about, and even if the model predicted decrease of 0.7 units occurs, the water will still be alkaline.

An independent reconstruction, again based on corals, shows that between 1708 and 1988, there was a clear interdecadal oscillation of pH, (between 7.9 and 8.2 pH units) which is synchronous with the Interdecadal Pacific Oscillation of water temperature.(4) During this time, atmospheric CO₂ concentration increased by about 100 parts per million. If more CO₂ is dissolved in the ocean, the added carbonate (to build the calcium carbonate shells) will more than offset the decreasing alkalinity. (5) The effect of increased CO₂ seems benign to other small sea creatures, including corals. (6)

The specter of acidification seems irrelevant to carbonate-shelled animals. What of fish and fish larvae? A study by Munday et al. (7) found CO₂ acidification had no detectable effect on embryonic duration, egg survival and size at hatching. As for adult fish, they found that most shallow-water fish tested to date appear to compensate fully their acid-base balance within several days of exposure to elevated CO2 concentrations.

Recent claims by climate change alarmists have raised the possibility that terrestrial ecosystems and particularly the oceans have started losing part of their ability to absorb a large proportion of man-made CO₂ emissions. However, a new study combines data from ice cores, direct atmospheric measurements, and emission inventories to show that the fraction of human emitted CO₂ that remains in the atmosphere has stayed constant over the past 160 years, at least within the limits of measurement uncertainty. (8)

Can the oceans ever become very acidic? There is no evidence that the oceans were ever acidic during the past 500 million years, even when atmospheric concentration of carbon dioxide was more than 10 times current levels. This implies that besides temperature and partial-pressure, there is a third controlling factor. That factor is the buffering effect of carbonic acid reaction with the basaltic oceanic crustal rocks. This process uses up excess carbon dioxide.

Ocean acidification is just another scary scenario, a phantom menace.

Sources:

1. Berner, R.A. and Kothavala, Z., 2001, A revised model of atmospheric CO₂ over Phanerozoic time: Am. J. Sci., v. 301, p. 182-204.

2. Caldeira, K. and Wickett, M.E. 2003. Anthropogenic carbon and ocean pH. Nature 425: 365.

3. Liu, Y., Liu, W., Peng, Z., Xiao, Y., Wei, G., Sun, W., He, J. Liu, G. and Chou, C.-L. 2009. Instability of seawater pH in the South China Sea during the mid-late Holocene: Evidence from boron isotopic composition of corals. Geochimica et Cosmochimica Acta 73: 1264-1272.

4. Pelejero, C., Calvo, E., McCulloch, M.T., Marshall, J.F., Gagan, M.K., Lough, J.M. and Opdyke, B.N. 2005. Preindustrial to modern interdecadal variability in coral reef pH. Science 309: 2204-2207.

5. Gutowska, M.A., Pörtner, H.O. and Melzner, F. 2008. Growth and calcification in the cephalopod Sepia officinalis under elevated seawater pCO2. Marine Ecology Progress Series 373: 303-309

6. Kurihara, H., Ishimatsu, A. and Shirayama, Y. 2007. Effects of elevated seawater CO2 concentration of the meiofauna. Journal of Marine Science and Technology 15: 17-22

7. Munday, P.L., Donelson, J.M., Dixson, D.L. and Endo, G.G.K. 2009. Effects of ocean acidification on the early life history of a tropical marine fish. Proceedings of the Royal Society B 276: 3275-3283.

8. Knorr, W. (2009), Is the airborne fraction of anthropogenic CO2 emissions increasing?, Geophys. Res. Lett., 36, L21710, doi:10.1029/2009GL040613.