How does rising atmospheric CO2 affect marine organisms?

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Four Centuries of ENSO Activity Reconstructed From Coral 18O Data
Evans, M.N., Kaplan, A. and Cane, M.A. 2002. Pacific sea surface temperature field reconstruction from coral 18O data using reduced space objective analysis. Paleoceanography 17: U71-U83.

What was done
The authors employed "a systematic methodology for the reconstruction of climate fields from sparse observational networks of proxy data" to reconstruct gridded Pacific Ocean sea surface temperatures from coral stable isotope (18O) data for the period 1607-1990.

What was learned
The latter half of the 400-year record was deemed to be the most reliable. Moving backward in time from the end of this most recent 200-year period, it was determined that ENSO activity "was more frequent after 1980, lower in the 1940-1975 epoch, and again more frequent around the beginning of the 1900s." It was additionally determined that "the 1860-1880 period was relatively quiescent," while "the 1820-1860 period was also a period of relatively vigorous ENSO activity." In fact, the authors described the earliest of these periods of intense ENSO activity, i.e., that of 1820-1860, as being "similar to [that] observed in the past two decades."

What it means
The authors say that "as these observations extend at least into the preindustrial period, attribution of the unusually ENSO-rich past few decades may lie in part with natural variability." Indeed, the cause of the heightened ENSO activity of the past two decades probably resides totally in natural variability, since the planet (or at least the Northern Hemisphere) has warmed considerably over this 200-year time span, according to the most reliable 1200-year earth temperature history yet to be developed (Esper et al., 2002), yet ENSO activity has not materially increased over this period. With essentially the same degree of ENSO activity at the beginning of the 19th century (when Little Ice Age temperatures prevailed) and at the end of the 20th century (when Modern Warm Period temperatures prevailed), it is abundantly clear that the most recent spate of intense ENSO activity cannot be attributed to planetary warmth; for there was just as much ENSO activity during the early 19th century portion of the Little Ice Age as there has been recently.

Esper, J., Cook, E.R. and Schweingruber, F.H. 2002. Low-frequency signals in long tree-ring chronologies for reconstructing past temperature variability. Science 295: 2250-2253.

Reviewed 26 June 2002