SIO40lecture15

SIO40lecture15 - SIO 40 Life and Climate on Earth Nov. 1st,...

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SIO 40 – Life and Climate on Earth Nov. 1st, 2010 Lecture 15 – Recent climate variations Can climate change be rapid?
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Lecture Outline -The Younger Dryas event -Climate tipping points? -The Little Ice Age Influence of volcanoes and sun spots on climate -Present day climate variability Ocean-atmosphere oscillations - ENSO
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Alley, Scientific American 2004 Very large, rapid temperature fluctuations were common during the last glaciation, and during the transition to interglacial conditions at the start of the Holocene, about 10,000 years ago. Ice core temperature records from Greenland show major climatic reversals (the Younger Dryas) as well as smaller but significant climate oscillations during the Holocene. More detailed high resolution analysis of Greenland ice core records has indicated that the Younger Dryas event happened very rapidly, on the time scale of decades.
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Alley, Scientific American 2004 What contributes to climate variability? 2. Thermohaline circulation Was the Younger Dryas caused by a shutdown of the North Atlantic conveyor?
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Alley, Scientific American 2004 In the case of the Younger Dryas, it is believed that a conveyor shutdown was caused as a result of massive freshwater influx to the North Atlantic during the most recent deglaciation period. Conveyor reductions or shutdowns may also be caused by changed in the hydrological cycle, or melting of the Greenland Ice Sheet.
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Are there climate “tipping points”? For more on this topic see “Runaway Tipping Points of No Return" on Realclimate.org . The term ‘‘tipping point’’ commonly refers to a critical threshold at which a tiny perturbation can qualitatively alter the state or development of a system. The influence of tipping points can be shown schematically (top right), when the stability landscape is poised such that a small perturbation will force the climate system (symbolized by the balls) to shift between several potential stable states. ‘‘Abrupt climate change’’, such as the Younger Dryas event, has been defined as occurring ‘‘when the climate system is forced to cross some threshold, triggering a transition to a new state at a rate determined by the climate system itself and faster than the cause’’. Shown at bottom right is an example for the North Atlantic conveyor belt circulation. Model runs forced by a 4-fold linear increase of atmospheric CO 2 over 50,000 years eventually cause the circulation to collapse without early warning.
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The Little Ice Age “Hunters in the Snow” by Bruegel the Elder, 1565 The Little Ice Age was a period of cold climate (between 0.5-1 ° C cooler relative to modern times),
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SIO40lecture15 - SIO 40 Life and Climate on Earth Nov. 1st,...

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