CLIMATOLOGY

Beat Generation

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Science  06 Apr 2001:
Vol. 292, Issue 5514, pp. 15
DOI: 10.1126/science.292.5514.15c

Many records of North Atlantic climate show that the cold conditions that prevailed during the last glacial period were interrupted by rapid shifts to warmer conditions and nearly equally rapid returns back to cold. This pattern is commonly considered to have been caused by reversals of the ocean's thermohaline circulation. These events were neither periodic nor stochastic (random); while they often occurred at intervals of approximately 1500 years, they sometimes skipped a beat or two and recurred instead at an integral multiple of 1500 years.

Alley et al. suggest that “stochastic resonance” may underlie this pattern. In this scenario, a weak, periodic forcing of 1500 years, not strong enough itself to trigger a reversal of oceanic thermohaline circulation, interacts with random forcing events that originate with the extensive ice sheets that covered so much of the high-latitude Northern Hemisphere. When a random event of sufficient strength occurs at the right time within the periodic cycle, the combination changes ocean circulation and triggers a climate reversal. The statistical distributions of rapid climate changes recorded in the GRIP and GISP2 ice cores from Greenland appear to be consistent with this hypothesis. — HJS

Paleoceanography16, 190 (2001).

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