Bond Events, Dansgaard-Oeschger events, Climate Cycles, and stuff
Posted by greg2213 on January 7, 2011
Pretty much everyone agrees that the warming we’ve seen over the last 130 year or so is on the order of .7C. The argument is over what caused it and where it’s going.
So then what would one make of increases, and declines, that are ten times (or more) greater and that happen in 1/10th the time (or less?) (Also see 1500 year cycles.)
WUWT have a nifty post covering some of these events and there’s more good stuff in the comments.
“Recent scientific evidence shows that major and widespread climate changes have occurred with startling speed. For example, roughly half the north Atlantic warming since the last ice age was achieved in only a decade, and it was accompanied by significant climatic changes across most of the globe. Similar events, including local warmings as large as 16°C, occurred repeatedly during the slide into and climb out of the last ice age. Human civilizations arose after those extreme, global ice-age climate jumps.”
“The new paradigm of an abruptly changing climatic system has been well established by research over the last decade, but this new thinking is little known and scarcely appreciated in the wider community of natural and social scientists and policy-makers.” (“Abrupt Climate Change – Inevitable Surprises”, Committee on Abrupt Climate Change, National Research Council of the National Academy of Sciences, 2002, ISBN: 0-309-51284-0, 244 pages, Richard B. Alley, chair.)
The rest: On “Trap-Speed”, ACC and the SNR
Vostok Ice Core, Antarctic: (click to enlarge)
At the recent end of the climate cycle there is the Younger Dryas event. The Earth was emerging from the last ice age, things were warming up, and the it rapidly dropped into full=blown ice age conditions for another 1200 years.
Apparently the recovery was pretty rapid, too.
What caused it? No one knows. Some have an impact hypothesis, and there’s an idea that giant glacial lakes flooded the Northern Atlantic with fresh water, cutting off all circulation, leading to the cooling. The problem is that the lake outflow seems to have been blocked by ice. From the comments:
This one has been out there for some time and keeps being repeated, but Thomas V Lowell showed that the St Lawrence River was blocked by ice during the Younger-Dryas. [Revised Deglacial Chronology of the Laurentide Ice Sheet and Implications for Catastrophic Meltwater Discharge as Triggers for Abrupt Climate Change,” Eos Trans AGU 86 (52) Fall Meet. Supple., Abstract (2005): F1234″ — This from “Sudden Cold” by climatologist Rodney Chilton (2009)]
A second study that involved a simulation of meltwater originating from the Laurentide Ice Sheet did not produce any appreciable meltwater during the entire 15,000 to 8,000 BP interval. [T.C. Moore (2000)]
The northern route at least appears to have suffered the same fate as the St. Lawrence in also being blocked by ice until well after the Younger-Dryas ended. [Thomas V. Lowell, ibid]