NCPA - National Center for Policy Analysis


June 21, 2005

A new study of the weaning weights of California's elephant seal pups predicts that a 25-year trend of Pacific Ocean warming has ended.

That means that the second half of a 50-year cycle has begun to cool the northern Pacific. In addition, historical fish catch data indicates the ocean cooling trend is likely to last until about 2025.

Burney Le Boeuf and David Crocker (University of California, Santa Cruz) monitored the weaning weights of central California seal pups for 29 years, from 1975 to 2004. The ocean's temperatures generally increased, and the pups' weaning weights declined 21 percent over 24 years from the study's beginning until 2000.

  • The seal pups' weight decline coincided with an increase in their mothers' foraging time of 36 percent.
  • A decline in the mother's own weights confirmed that fish were relatively scarce.
  • After 1999, however, ocean temperatures began to decline, fish became more abundant and the pups' weaning weights abruptly began to rise.
  • By 2004 the pups weaning weights had recovered to 90 percent of their 1975 weaning size.

The previous shift toward warmer temperatures, which disadvantaged the California seal pups occurred in the mid-1970s. Researchers have begun to call the 50-year ocean cycle the Pacific decadal oscillation (PDO).

During the PDO, ocean temperatures rise and fall, fish species wax and wane, and fish are caught in different places, but total ocean productivity remains stable.

What does it all mean? Seal pups are instructing us that even temperature trends as long as 25 years can mislead us about cause and effect in the Earth's climate -- which has been cycling constantly for at least the last million years, say observers.

Source: Dennis Avery, "Trust Seal Pups' Assessment of Climate," Investor's Business Daily, June 20, 2005; based upon: Burney Le Boeuf and Daniel E Crocker, "Ocean climate and seal condition," University of California, Santa Cruz, March, 28, 2005.

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