How does rising atmospheric CO2 affect marine organisms?

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The Medieval Warm Period in Panama
Lachniet, M.S., Burns, S.J., Piperno, D.R., Asmerom, Y., Polyak, V.J., Moy, C.M. and Christenson, K.  2004.  A 1500-year El Niņo/Southern Oscillation and rainfall history for the Isthmus of Panama from speleothem calcite.  Journal of Geophysical Research 109: 10.1029/2004JD004694.

What was done
The authors generated a high-resolution oxygen-isotope rainfall record of the Central American Monsoon for the Isthmus of Panama from a U/Th-dated stalagmite that spanned the period 180 BC to AD 1310.

What was learned
Lachniet et al.'s data reveal pronounced hydrologic anomalies during medieval times, with the driest conditions occurring between AD 900 and 1310, but especially during the AD 1100-1200 "High Medieval," when western European temperatures were reported, in their words, to be "anomalously high."

What it means
The authors conclude that "the correspondence between warm medieval temperatures and dry hydrologic anomalies in Panama supports a large-scale Medieval Climatic Anomaly that may have been global in extent, and involved atmospheric circulation reorganizations that are linked to ENSO."  We agree, noting that such reorganizations of earth's climate system are not dependent on rising atmospheric CO2 concentrations to trigger them, and, therefore, that the development of the Modern Warm Period likely was largely unrelated to the concomitant increase in the air's CO2 concentration, being forced instead primarily by a return engagement of whatever led to the development of the Medieval Warm Period.

Reviewed 5 January 2005