Climate Beginning to Cool, Seal Pup Data Indicate

Published August 1, 2005

A new study of California elephant seal pups and their weaning weights suggests a 25-year Pacific Ocean warming has ended and the second half of a 50-year cycle has begun to cool the northern Pacific. Historical fish catch data indicate the ocean cooling trend is likely to last until about 2025.

Weight Linked to Temperature

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

The seal pups’ weight decline coincided with an increase in their mothers’ foraging time of about 36 percent. A decline in the mothers’ own weights confirmed that fish were relatively scarce.

After 1999, however, ocean temperatures began to fall, 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.

Salmon, Sardine Data Agree

The seal pup weight trends confirm a cycle also found in northern Pacific salmon catches. Columbia River salmon numbers declined sharply after 1977. Columbia River salmon catch data, which date back to 1900, clearly reveal 50-year cycles, with 25-year periods of salmon abundance interspersed with 25-year periods of salmon scarcity.

The Gulf of Alaska salmon catch data show a similar but opposite cycle. When the Columbia salmon fishery is down, the Alaskan salmon numbers are up.

Dr. Francisco Chavez of the Monterey Bay Aquarium led a 2003 study that found shifts in sardine and anchovy populations across the Pacific Ocean followed the same 50-year cycle, and did so in such widely separated places as California, Peru, and Japan, with sharply different fishing pressures.

Chavez’s data show the most recent shift, toward cooler temperatures that favored anchovies over sardines, occurred in the late 1990s. The previous shift toward warmer temperatures, which disadvantaged the California seal pups and anchovies, occurred in the mid-1970s.

Temps Vary in Cycle

Researchers have begun to call the 50-year ocean cycle the Pacific Decadal Oscillation (PDO). Temperatures rise and fall, fish species wax and wane, and the fish are caught in different places, but total ocean productivity remains relatively stable.

Do the seals, salmon, and sardines have something to tell us about man-made global warming? The Earth’s temperatures have increased since 1850–the end of the widely noted Little Ice Age–by about 0.8 degrees Celsius. However, 0.6 degrees C of the warming occurred before 1940, and thus before much human-emitted CO2.

After 1940, the Earth’s temperature declined moderately until the late 1970s, despite significant increases in human CO2 emissions and in defiance of the greenhouse theory. During this period, the PDO was cooling the Pacific.

Niños Track Global Temps

The Earth’s warmest years generally occur during Pacific El Niños. Cooler years accompany La Niñas.

Explains Richard Hagan of the National Oceanic and Atmospheric Administration, “When the PDO is in the cold phase … meaning surface layer water temperatures are colder than normal over a large area of the Pacific … La Niña events predominate. The reverse is true for the warm phase, i.e., El Niño events predominate.

“This is demonstrated quite well in the [accompanying] graph. The PDO was in the cold phase from 1947 to 1976 … and La Niña events dominated. Since 1976 thru 1999 … the PDO has been in the warm phase and El Niño events of unusual strength and long tenure have dominated.”

Niña Return Possible

“There has been considerable speculation over the past year that the PDO is switching back to the cold phase,” added Hagan. “Each phase of the PDO has its unique impacts on global and U.S. weather. For the southwestern U.S., including deep south Texas, the cold phase of the PDO results in overall warm winters but with some notable cold outbreaks.”

The current surge of public concern about human-caused global warming occurred after the Earth’s average temperatures began to rise again in the late 1970s, which coincided with the PDO’s shift back to its ocean-warming phase.

Does the recent shift in the PDO mean the Earth’s average temperatures will start to cool again? Was the “warmest decade” of the 1990s an artifact of expanding urban heat islands and a 25-year Pacific Ocean warming phase?

Seal pups and sardines indicate this is entirely possible.

Data Expose Theory’s Weaknesses

“The seal data is just one more piece of evidence exposing weaknesses in the theory of human-caused warming,” said Sterling Burnett, senior fellow at the National Center for Policy Analysis. “It doesn’t refute the idea that the Earth has warmed, but it does call into question the extent of human influence on recent moderate warming.

“Nature has a much larger role in warming than activist groups give it credit for,” Burnett added. “Alarmist global warming theory is little more than a house of cards, and each time science enters the debate, another card is removed from the shaky foundation the alarmists [have built].”

Dennis T. Avery ([email protected]) is a senior fellow of the Hudson Institute and an adjunct scholar with the National Center for Policy Analysis. He is writing a book, with climate researcher S. Fred Singer, on the physical evidence of Earth’s natural 1500-year climate cycle.