Wednesday, August 1, 2012

Another day, another non-hockey-stick

A paper published in the current issue of Nature Climate Change reconstructs sea surface temperatures [SSTs] in the southwest tropical pacific from 1649-2000. The paper finds SSTs varied with the Pacific Decadal Oscillation, but were not correlated to solar activity. Figure 2 of the paper is shown below and indicates some periods during the Little Ice Age were as warm or warmer [e.g. from ~1690-1700] than the late 20th century.
Reconstructed SSTs in top graph

Sea surface temperature variability in the southwest tropical Pacific since AD 1649

Nature Climate Change

A prime focus of research is differentiating the contributions of natural climate variability from those that are anthropogenically forced, especially as it relates to climate prediction123. The short length of instrumental records, particularly from the South Pacific, hampers this research, specifically for investigations of decadal to centennial scale variability14. Here we present a sea surface temperature (SST) reconstruction derived from highly reproducible records of strontium-to-calcium ratios (Sr/Ca) in corals from New Caledonia to investigate natural SST variability in the southwest tropical Pacific from AD 1649–1999. Our results reveal periods of warmer and colder temperatures of the order of decades during the Little Ice Age that do not correspond to long-term variations in solar irradiance or the 11-year sunspot cycle. We suggest that solar variability does not explain decadal to centennial scale SST variability in reconstructions from the southwest tropical Pacific. Our SST reconstruction covaries with the Southern Hemisphere Pacific decadal oscillation5 and the South Pacific decadal oscillation6, from which SST anomalies in the southwest Pacific are linked to precipitation anomalies in the western tropical Pacific6. We find that decadal scale SST variability has changed in strength and periodicity after 1893, suggesting a shift in natural variability for this location.

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