How does rising atmospheric CO2 affect marine organisms?

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The Climate of Central Alaska During the Last Interglacial
Muhs, D.R., Ager, T.A. and Begét, J.E.  2001.  Vegetation and paleoclimate of the last interglacial period, central Alaska.  Quaternary Science Reviews 20: 41-61.

What was done
The authors present proxy climate data for central Alaska during the previous interglacial and compare their results with those obtained by other authors for the same region and time period.

What was learned
Analysis and synthesis of the authors' data with results reported elsewhere created an "overall picture that emerges for Alaska and Yukon during the peak warmth of the last interglacial [as] a region with warmer-than-present summers, an absence of permafrost in the interior, and probably greater precipitation in the interior."  How much warmer was it?  Based upon the expanded boreal forest ranges in this area, the authors estimate that summer temperatures were at least 1-2°C warmer than they are presently, and that in some locations summer temperatures may have been as much as 3-5°C higher than they are now.

What it means
Reports of disappearing permafrost in Alaska are often claimed to be evidence of CO2-induced global warming.  It is clear from this study, however, that Alaska has experienced periods of time throughout its history that have been significantly warmer than it is currently; and some, such as this one, occurred at times when the air's CO2 concentration was much lower than it is today.  See, for example, Climate Change (CO2-Temperature Correlations) in our Subject Index.  And if it's happened before, it can happen again.  Melting permafrost in Alaska may well be indicative of local warming; but that warming need not be caused by rising atmospheric CO2 concentrations.  Just as there's more than one way to skin a cat, there are a lot of ways to make a warmer climate.