How does rising atmospheric CO2 affect marine organisms?

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A 1400-Year Record of ENSO Variability
Eltahir, E.A.B. and Wang, G.  1999.  Nilometers, El Niņo, and climate variability.  Geophysical Research Letters 26: 489-492.

What was done
The level of water in the Nile river was examined as a proxy for El Niņo episodes over the past 14 centuries in an effort to determine if there has been a recent unprecedented trend towards an increasing frequency of El Niņo events.

What was learned
The authors report that the frequency of El Niņo events over the last two decades has been high, but it is similar to trends observed near the start of the century.  The average duration of recent El Niņos, however, was found to be longer toward the end of the century than in the beginning.  Yet here, too, such occurrences were not found to be without precedent; "similar levels of activity were experienced during the last three centuries of the first millennium."

What it means
This study demonstrates that the El Niņo events of the last two decades are not without historical precedent.  Such results suggest caution in attributing recent El Niņo events to CO2-induced global warming, especially when similar events have occurred when earth's atmospheric CO2 concentration was 90 ppm lower than it is presently.

Reviewed 15 May 1999