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Cyclical Climate Change in Iberia
Reference
Desprat, S., Goņi, M.F.S. and Loutre, M.-F.  2003.  Revealing climatic variability of the last three millennia in northwestern Ibera using pollen influx data.  Earth and Planetary Science Letters 213: 63-78.

What was done
The authors studied the climatic variability of the last three millennia in northwest Iberia via a high-resolution pollen analysis of a sediment core retrieved from the central axis of the Ria de Vigo in the south of Galicia (42°14.07'N, 8°47.37'W).

What was learned
Over the past 3000 years there was, in the words of the authors, "an alternation of three relatively cold periods with three relatively warm episodes."  In order of their occurrence, these periods are described by Desprat et al. as the "first cold phase of the Subatlantic period (975-250 BC)," which was "followed by the Roman Warm Period (250 BC-450 AD)," which was followed by "a successive cold period (450-950 AD), the Dark Ages," which "was terminated by the onset of the Medieval Warm Period (950-1400 AD)," which was followed by "the Little Ice Age (1400-1850 AD), including the Maunder Minimum (at around 1700 AD)," which "was succeeded by the recent warming (1850 AD to the present)."  Desprat et al. additionally conclude that "solar radiative budget and oceanic circulation seem to be the main mechanisms forcing this cyclicity in NW Iberia."

What it means
As time progresses and paleoclimatic studies increase in both number and sophistication, ever more evidence is accumulating for the global reality of the solar-induced millennial-scale oscillation of climate that pervades both glacial and interglacial periods alike.  In this specific instance, Desprat et al. report that "a millennial-scale climatic cyclicity over the last 3000 years is detected for the first time in NW Iberia paralleling global climatic changes recorded in North Atlantic marine records (Bond et al., 1997; Bianchi and McCave, 1999; Chapman and Shackelton, 2000)."  The establishment of the Modern Warm Period over the course of the past century is consequently seen to be nothing more than the most recent manifestation of this ever-recurring phenomenon and, hence, is likely totally unrelated to the concurrent historical increase in the air's CO2 content.

References
Bond, G., Showers, W., Cheseby, M., Lotti, R., Almasi, P., de Menocal, P., Priore, P., Cullen, H., Hajdas, I. and Bonani, G.  1997.  A pervasive millennial-scale cycle in North Atlantic Holocene and glacial climates.  Science 278: 1257-1266.

Chapman, M.R. and Shackelton, N.L.  2000.  Evidence of 550-year and 1000-year cyclicities in North Atlantic circulation patterns during the Holocene.  The Holocene 10: 287-291.

Bianchi, G.G. and McCave, I.N.  1999.  Holocene periodicity in North Atlantic climate and deep-ocean flow south of Iceland.  Nature 397: 515-517.


Reviewed 22 October 2003