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PDO-ENSO interactions over the past four centuries

04 Oct 2023 | Science Notes

From the CO2Science Archive: The authors used “proxy climate records derived from paleoclimate data to investigate the long-term behaviour of the Pacific Decadal Oscillation (PDO) and the El Niño Southern Oscillation (ENSO).” Over the past 400 years, Verdon and Franks report that climate shifts associated with changes in the PDO “occurred with a similar frequency to those documented in the 20th century.” In addition, and more importantly, they find that “phase changes in the PDO have a propensity to coincide with changes in the relative frequency of ENSO events, where the positive phase of the PDO is associated with an enhanced frequency of El Niño events, while the negative phase is shown to be more favourable for the development of La Niña events.”

Paper reviewed: Verdon, D.C. and Franks, S.W. 2006. Long-term behaviour of ENSO: Interactions with the PDO over the past 400 years inferred from paleoclimate records. Geophysical Research Letters 33: 10.1029/2005GL025052.

What it means
The two Australian scientists note that the numerous El Niño events of the recent past “have been reported as unusual, and have even been suggested to be possible evidence of anthropogenic climate change [e.g., Trenberth and Hoar, 1996].” However, as they continue, “the paleo records suggest that the apparent lack of La Niña events and high frequency of El Niño events over the past two decades may not be abnormal and could be attributed to the fact that during this time the PDO has been in a positive phase,” such that “when the PDO switches back to a negatively dominated phase, it is quite likely that the frequency of La Niña events will increase once again.” Consequently, there is no compelling reason to believe that the recent preponderance of El Niño events over La Niña events is a “fingerprint” of CO2-induced global warming.

Trenberth, K.E. and Hoar, T.J. 1996. The 1990-1995 El Niño-Southern Oscillation event: Longest on record. Geophysical Research Letters 23: 57-60.

One comment on “PDO-ENSO interactions over the past four centuries”

  1. Two things. If it's settled it isn't science. And. The minimum we are now in is being referred to as the Modern Minimum. Methinks it should have a proper name like the Maunder Minimum does. It's just a suggestion, but I was thinking, how about the Gore Minimum. After all he was the one that got many like myself interested enough to look at the actual science in some detail. I quickly learned that if there was zero carbon dioxide in the air all the plants would die, shortly followed by everything that directly or indirectly ate them, like us. Oh and yes, fortunately, atmospheric carbon dioxide does indeed keep the Earth warmer than it would be without it. -100 deg. C on average. (I'm open to correction on this as I don't know the exact number.) I also learned that the relationship between the Earth's surface temperature and the concentration of carbon dioxide in the atmosphere is not linear, its exponential. So every CO2 increase has less effect than the one before and ultimately a point is reached where adding more CO2 to the atmospheric does not increase atmospheric temperature at all. (Saturation.)

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