Daily Archives: July 22, 2009

More on Abrupt Climate Change: The H1 to BA transition

One of the most interesting parts of the paleoclimate record over the last 100,000 years, is the series of abrupt climate changes prior to the Holocene that have occurred on very rapid timescales, ranging from years to decades (Alley et al, 2003). These changes were large, fast, and occurred when the climate was pushed across certain thresholds.

Of particular note, is the well over 20 Dansgaard-Oeschger events since the last interglacial. Typically, a rapid warming on timescales of decades was followed by slower cooling, rapid cooling, and then a brief period of little temperature change. A value near 1500 years between these events is common, although sometimes there are skips and so the spacing could be a scalar multiple of near 1500 years. Successive D-O oscillations become progressively cooler as the cold-based ice sheet grows in Hudson Bay, and when the base of the ice thaws, you get a Heinrich event surge that dumps large number of icebergs that calved from the Laurentide ice sheet into the North Atlantic, via the Hudson Straight (or perhaps other sources such as the Icelandic and British Isles ice sheet). This succession of progressively cooler D-O events, punctuated by a Heinrich event (until the next cycle begins or the climate becomes too warm for an ice sheet to grow) is a Bond cycle. These events are common before the Holocene which led to a climate punctuated by high-frequency variations and a much more variable situation than that which humans have enjoyed over the past 10,000 years.

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