How does rising atmospheric CO2 affect marine organisms?

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The Climatic History of the Phanerozoic
Boucot, A.J., Xu, C. and Scotese, C.R.  2004.  Phanerozoic climatic zones and paleogeography with a consideration of atmospheric CO2 levels.  Paleontological Journal 38: 115-122.

What was done
The authors compiled over 7000 data points from over 4000 references dealing with "climatically sensitive deposits (chiefly evaporites, calcretes, coals, bauxites, kaolins and kaolinites, tillites, dropstones, glendonites and cool-water marine sediments, palms, as well as crocodilians etc.) through twenty-seven Phanerozoic time intervals," which effort enabled them "to revise the contemporary paleogeography in a manner consistent with the climatic information."  Then, they compared "the changing Phanerozoic global climatic gradients based on geological evidence with the previously published models of Phanerozoic atmospheric CO2 based on geochemical assumptions."

What was learned
Boucot et al. report finding "many inconsistencies between the two approaches, such as the moderate global climatic gradient from the Middle Cambrian through the earlier Middle Devonian (Eifelian) versus the very high level of atmospheric CO2 during the same time interval provided by the geochemical model [Berner, 1997] which suggests an exceptionally low global climatic gradient."

What it means
The authors of this intriguing paper conclude that "either the assumptions on which the geochemical models are based are erroneous or that atmospheric CO2 is not a greenhouse gas," saying "we prefer the former possibility."  We simply caution that the monumental amount of published data Boucot et al. analyzed in coming to this tremendous "fork in the road" suggests that the other possibility ought not be discarded out of hand.  Another reason for exercising caution in this regard is the great amount of independent evidence we have reviewed on our website that suggests that the real-world greenhouse powers of CO2 have been vastly overestimated by the Intergovernmental Panel on Climate Change, particularly within the context of the many potential negative feedbacks (some of biological origin) that may operate in nature to curtail CO2's pristine influence, which would otherwise be felt more significantly.

Berner, R.A.  1997.  The rise of plants and their effect on weathering and atmospheric CO2Science 276: 544-546.

Reviewed 16 March 2005