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Sea Surface Temperature Trends at Monterey Bay, USA
Reference
Breaker, L.C.  2005.  What's happening in Monterey Bay on seasonal to interdecadal time scales?  Continental Shelf Research 25: 1159-1193.

What was done
The author performed a number of statistical analyses on a daily sea-surface temperature (SST) record from the Hopkins Marine Station in Pacific Grove, California, located at the southern end of Monterey Bay, for the period 1920-2001.  The intent of the study was to identify and estimate the relative importance of atmospheric and oceanic processes that contribute to the variability in the SST record from seasonal to interdecadal time scales.

What was learned
Based on monthly averages, variability in the Pacific Grove data was accounted for as follows: approximately 44% came from the annual cycle, 18% from El Niņo warming episodes, 6% from the Pacific Decadal Oscillation (PDO), 4% from the long-term trend, and 3% from the semiannual cycle.  Linear analysis of the 82-year record revealed a statistically significant SST increase of 0.01°C per year, which trend is similar to the findings of other researchers who have attributed the trend to global warming (Barry et al., 1995; Sagarin et al., 1999).  However, additional analyses conducted by Breaker suggest that this attribution may have been a bit premature.

In further examining the Pacific Grove SST data, Breaker found there were two major regime shifts associated with the PDO over the course of the record, one at about 1930 and one in 1976, which could explain most of the 82-year warming.  Prior to the regime shift in the vicinity of 1930, for example, the waters of Monterey Bay were, in Breaker's words, "much colder than at any time since then."  Furthermore, if one computes the linear SST trend subsequent to this regime shift, which Beaker did, the resulting 72-year trend is a non-statistically significant +0.0042°C.  As a result, Beaker concludes that "although the long-term increase in SST at Pacific Grove appears to be consistent with global warming, the integrated anomaly suggests that temperature increases in Monterey Bay have occurred rather abruptly and thus it becomes more difficult to invoke the global warming scenario."

What it means
The results of this study clearly demonstrate that decadal-scale regime shifts have the potential to totally dwarf any potential "fingerprint" of CO2-induced global warming that might possibly be present in many 20th-century SST data sets.  Also, it is clear that the regime shift in the vicinity of 1930 in this data set was not the product of anthropogenic global warming, because so little of the current burden of anthropogenic greenhouse gases had been released to the atmosphere prior to that time compared to what was subsequently released.  Consequently, until we can get a much better understanding of the causes and consequences of natural decadal-scale climatic oscillations, there will be no way to validate model predictions of CO2-induced global warming.

References
Barry, J.P., Baxter, C.H., Sagarin, R.D. and Gilman, S.E.  1995.  Climate-related, long-term faunal changes in a California rocky intertidal community.  Science 267: 672-675.

Sagarin, R.D., Barry, J.P., Gilman, S.E. and Baxter, C.H.  1999.  Climate-related change in an intertidal community over short and long time scales.  Ecological Monographs 69: 465-490.

Reviewed 19 October 2005