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North Atlantic Regime Shift: Is It Déjà Vu All Over Again?
Reference
Drinkwater, K.F. 2006. The regime shift of the 1920s and 1930s in the North Atlantic. Progress in Oceanography 68: 134-151.

What was done
The author says the objective of his paper is "to provide a review of the changes to the marine ecosystems of the northern North Atlantic during the 1920s and 1930s and to discuss them in the light of contemporary ideas of regime shifts," where he defines a regime shift as "a persistent radical shift in typical levels of abundance or productivity of multiple important components of the marine biological community structure, occurring at multiple trophic levels and on a geographical scale that is at least regional in extent."

What was learned
Drinkwater determined that "in the 1920s and 1930s, there was a dramatic warming of the air and ocean temperatures in the northern North Atlantic and the high Arctic, with the largest changes occurring north of 60°N," which warming "led to reduced ice cover in the Arctic and subarctic regions and higher sea temperatures," as well as northward shifts of multiple marine ecosystems.

The change in climate occurred "during the 1920s, and especially after 1925," according to Drinkwater, when "average air temperatures began to rise rapidly and continued to do so through the 1930s," as "mean annual air temperatures increased by approximately 0.5-1°C and the cumulative sums of anomalies varied from 1.5 to 6°C between 1920 and 1940 with the higher values occurring in West Greenland and Iceland." Thereafter, as he describes it, "through the 1940s and 1950s air temperatures in the northernmost regions varied but generally remained relatively high," declining in the late 1960s in the northwest Atlantic and slightly earlier in the northeast Atlantic, which cooling has only recently begun to be reversed in certain parts of the region.

In the realm of biology, the early 20th-century warming of North Atlantic waters "contributed to higher primary and secondary production," in the words of Drinkwater, and "with the reduced extent of ice-covered waters, more open water allow[ed] for higher production than in the colder periods." As a result, cod "spread approximately 1200 km northward along West Greenland," and "migration of 'warmer water' species also changed with earlier arrivals and later departures." In addition, Drinkwater notes that "new spawning sites were observed farther north for several species or stocks while for others the relative contribution from northern spawning sites increased." Also, he writes that "some southern species of fish that were unknown in northern areas prior to the warming event became occasional, and in some cases, frequent visitors."

In conclusion, and considering all aspects of the event, Drinkwater concludes that "the warming in the 1920s and 1930s is considered to constitute the most significant regime shift experienced in the North Atlantic in the 20th century."

What it means
Climate-alarmist claims of recent unprecedented warming in parts of the Arctic and the equally unprecedented effects they claim it is having on Arctic ecosystems are simply uninformed and errantly understood exaggerations. The things we are seeing in the Arctic today have occurred before, even within the past century; but being outside the realm of most people's personal recollection, climate alarmists refuse to acknowledge that these things are simply naturally-recurring phenomena associated with the most recent warming phase of a repeating climatic oscillation that is currently enhancing biological activity and productivity in a rejuvenating "double-plus" for the biosphere.

Reviewed 5 April 2006