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Author Topic: Past rapid temperature rises in Greenland's past  (Read 2233 times)

LRC1962

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Past rapid temperature rises in Greenland's past
« on: December 10, 2014, 07:03:28 AM »
Have been watching several talks on youtube by Richard Alley. A few times he mentioned rapid temp rises that have happened in Greenlands past. One such occurrence was the Younger Dryas. Temp changes happened within a decade or 2 or sometimes in a year or 2 based on the evidence and the rises in temp were of the order of +15C.  RA tends to be an optimist by nature and avoids bad scenarios like the plague, so he would of course would say that he does not think that conditions are not right for it happening in this century. He also thinks that there enough humpy ground under the GIS to hold the inner sheet stable. Based on that could it be possible that we could see such a rise in the near future and how damaging could that be to the inner GIS?
Note: I do not mean to disparage him in any way as he is very knowledgeable, but from his talks I do feel he tends to be a little too optimistic compared to some of the rest of his peer group.
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folke_kelm

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Re: Past rapid temperature rises in Greenland's past
« Reply #1 on: December 10, 2014, 10:30:51 AM »
could you please provide some links to his talks? I am simply far too lazy to search  ;)

LRC1962

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Re: Past rapid temperature rises in Greenland's past
« Reply #2 on: December 13, 2014, 05:42:04 AM »
One paper I found talks about it http://www.pnas.org/content/97/4/1331.full .
One example is starts about quick changes around 14min. Can not find the one which showed actual ice core.
Sorry but most videos I was watching was over 45min long and saw quite a few in sequence and can not remember which one it was.
can see changes in this graph
"All truth passes through three stages: First, it is ridiculed; Second,  it is violently opposed; and Third, it is accepted as self-evident."
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A-Team

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Re: Past rapid temperature rises in Greenland's past
« Reply #3 on: December 14, 2014, 12:40:39 AM »
Quote
Note: I do not mean to disparage RA in any way as he is very knowledgeable, but from his talks I do feel he tends to be a little too optimistic
Good plan. It's hard to argue with 225 journal publications from 1982-2013 on a broad range of cryosphere vs climate topics when the median academic scientist produces 0 papers a year and a few outliers write 1-2. While cryosphere research has taken the art of cross-collaborative multiple authorship to new heights and peer review by necessity is incestuous, this is still a lot of strong, frequently cited papers.

One recent RB Alley paper considers 'feasible solutions' to climate change. That could be taken as optimism, but optimism should include a likelihood of society actually taking up even modest proposals (which I rate as zero: train wreck coming). His complete CV is here:

http://www.geosc.psu.edu/sites/default/files/Alley_vita_long_aug13.pdf

LRC1962 writes, "One such occurrence was the Younger Dryas. Temp changes happened within a decade or 2 or sometimes in a year or 2 based on the evidence and the rises in temp were of the order of +15C."

More broadly, when paleo-climatologists says 'the earth system did this experiment already and nothing bad happened!' it's fair to ask 'how well do we really know what happened back then?' and 'did boundary conditions actually match up with today?'

It's one thing to claim Greenland didn't totally melt out during the (poorly characterized) Eemian but another to know what the previous stadial left behind, never mind that Arctic sea ice extent, rate of warming, insolation cycle place, AMOC, greenhouse gases, surface mass balance, general circulation etc etc may not actually have matched conditions today all that well. What then is the take-home lesson?

For the Younger Dryas transition data, there's a newish paper (PA Mayewski 2013 free full doi: 10.1002/jqs.2684). It revolves around an amazing new device at the Keck Laser Ice Facility in Maine that conducts inductively coupled laser ablation argon plasma mass spectroscopy of minor elements in ice cores (here the 21 year old GISP2) at 2-20 mm resolution.

That corresponds to near-daily event resolution which allows detection and description of individual storms 11,643 years ago (y2k).

The article (which cites 1993 and 1997 Alley papers) focuses on 25,739 samples of the 14 specific years that sandwich the 3 critical years between glacial conditions at the end of the Younger Dryas and the beginning of our equable Holocene climate via ppb calcium, sodium and iron. These are not brought in by volcanics but as ordinary dust and wind-borne vapor solutes.

Calcium is presumed a terrestrial dust indicator carried by zonal atmospheric circulation (westerlies) to Greenland either dissolved in water (carbonate) and as calcium sulfate dihydrate (gypsum dust), or if accompanied by sea salt potassium, by Siberian High easterlies.

Iron originates as crustal dust swept into the atmosphere is gradually solvated by water vapor and precipitated on the icestream surface. It did not change too much during the transition, indicating a different dust source.

Sodium, another atmospheric circulation proxy, derives from sea water and is brought to Greenland primarily via the Icelandic Low in soluble form. Like calcium, it primarily deposited in winter and spring storms.

It has previously been established that changes in atmospheric circulation preceded elevation in temperature. This study shows the YD/Holocene transition took place -- as far as calcium and sodium transport are concerned -- over a single year (GISP2 depths 1678.18– 1678.19 m). The authors, who have been at this for decades, conclude:

Quote
"Reduction in continental source calcium and iron and marine source sodium is consistent with northward migration and weakening of the westerlies and coupled easterlies associated with warming into the Holocene as the north–south thermal gradient weakened."
I gave my 2¢ about what caused the Younger Dryas transition earlier, not correlating it with about atmospheric circulation changes:

Quote
"Melting of the Laurentide Ice Sheet (at its peak, the size of Antarctica) had to have consequences. When moraine ice dams broke, the immense volumes of melt lakes didn't go quietly into the night ...While temporal correlation supports but does not prove causation, the Younger Dryas event in all likelihood was caused by a massive discharge in late summer of Lake Agassiz out the MacKenzie River into the Arctic Ocean."
http://forum.arctic-sea-ice.net/index.php/topic,154.msg34612.html#msg34612