A climatic roller coaster during the last Ice Age? Under certain conditions, noise can paradoxically increase a weak signal’s detectability and influence. This phenomenon, called stochastic resonance (SR), has been observed in settings as diverse as chaotic lasers and human reflex systems (see Physics Today, Physics Today 0031-9228 493199639 https://doi.org/10.1063/1.881491 March 1996, page 39 ). Andrey Ganopolski and Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research in Germany have shown that SR may have played a role in triggering 20 or so abrupt and dramatic warming events—called Dansgaard-Oeschger (DO) events—during the last Ice Age, which lasted from about 120 000 to 10 000 years before the present. Each DO event started with a roughly 10-year warming of about 10°C over the North Atlantic, and each lasted for up to a few centuries before cooling again. Curiously, the DO events typically were 1500 years apart,...

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