Arkeologi > Stenålder

Istidens abrupta dynamik

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Boreas:
Nogranna analyser av North-GRIP-proven visar att Grönland undergått "abrupta klimatändringar" under slutet av istiden. "Forandringene i klimaet var lynhurtige og dramatiske" konkluderer Sune O. Rasmussen ved Nils Bohrs Institut i Köpenhamn.

Den sista temperatur-ökningen, på ca. 10 grader Celsius, sägs nu ha avslutat istiden över norra Atlantern inom loppet av ett par år...

http://www.nbi.ku.dk/english/news/ice_cores_show_abrupt/

http://www.iceandclimate.nbi.ku.dk/publications/papers/
http://www.sciencedaily.com/releases/2008/06/080619142112.htm

Boreas:
Innan isen;

Tropiska Grönland;
http://ku-prism.org/polarscientist/losttribes/Jan131897Boston.htm

"Evig" tropnatt över Elsemere Island?
http://www.sciencedaily.com­/releases/2009/06/090601140932.htm

Under tiden;

Iskalottens termodynamiska processer;
http://www.sciencedaily.com/releases/2008/12/081222113522.htm

MIS 5 - N-Europa:
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VBC-4R718NB-1&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=941117776&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=12b2772082c3b9b7e2753a95b0afe13b

MIS 5 - Fennoskandia:
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VBC-4VNCJG1-2&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=25b786f506bc004eb0d5999a41496131

Finska istider;
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B7W57-4NJDG9W-B&_user=10&_origUdi=B6VBC-4VNCJG1-2&_fmt=high&_coverDate=12%2F31%2F2004&_rdoc=1&_orig=article&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=99b8f1a37a66fe30d9d6fb196395209e

Dynamiska uppfattnigar av LGM
http://www.nature.com/ngeo/journal/v2/n2/abs/ngeo411.html

Abrupt förkylning i Europa, 12.700 BP;
http://www.sciencedaily.com/releases/2008/08/080801152137.htm

Snabbt förkylda skandinaver - 11.300, 10.300, 9.400 och 8.200 BP;
http://instaar.colorado.edu/meetings/AW2008/abstract_detail.php?abstract_id=18

Boreas:
Efter isgången;

Lilla istiden - lokalt fenomen i NV Europa?!
http://www.grida.no/climate/ipcc_tar/wg1/070.htm

tty:
Nej, lilla istiden och MWP var inte några lokala nordvästeuropeiska fenomen. De är mycket väl historiskt dokumenterade i Japan och Kina och syns också mycket tydligt i t ex förändringar av trädgränsen i Nordamerika. De märks också här och var i tropikerna t ex i vattentemperaturerna i Lake Malawi och i den tempererade zonen på det södra halvklotet (t ex Patagonien och Nya Zeeland). Däremot verkar de inte vara märkbara i Antarktis.

Ditt citat är nog mera klimatpolitik än klimathistoria. Bara det faktum att man citerar Mann's ökända "Hockeyklubb-artikel" är ett varningstecken.   

Boreas:
Visst har klimatfrågan fört till en politisering av Michael E. Manns klimatanalyser från 1998 - och gjort hans s.k. "hockey-stick" omtvistad, speciellt av endera klima-skeptiker.
http://www.cicero.uio.no/fulltext/index.aspx?id=3680

Dock, det är knapt relevant för denna diskusion, som enbart använder datagrundlaget från "Mann, et al." som EN av många referenser.
http://holocene.meteo.psu.edu/shared/research/old/mbh98.html

(Nu har man givetvis ett bättre och brädare datagrundlag - vilket modifierat Manns uppgifter;
http://www.worldclimatereport.com/index.php/2005/03/03/hockey-stick-1998-2005-rip/)

Jeg kan dock inte se hur eller varför "Hockey-kurvan" skulle beröra diskussionen om isens termodynamiska närsmältning - och de dokumenterade variationer i utslag innom regioner, såväl som perioder. Artikkeln från GRID henvisar ju till en rad mätningar av såväl varma som kalla perioder inom dom senaste 1000 åren - varefter den pekar på det faktum at temperatur-svängningarna INTE följer en ensartat, global kurva - men utvisar klara regionala skillnader;


--- Citera ---Evidence from mountain glaciers does suggest increased glaciation in a number of widely spread regions outside Europe prior to the 20th century, including Alaska, New Zealand and Patagonia (Grove and Switsur, 1994).

However, the timing of maximum glacial advances in these regions differs considerably, suggesting that they may represent largely independent regional climate changes, not a globally-synchronous increased glaciation (see Bradley, 1999).

Thus current evidence does not support globally synchronous periods of anomalous cold or warmth over this timeframe, and the conventional terms of "Little Ice Age" and "Medieval Warm Period" appear to have limited utility in describing trends in hemispheric or global mean temperature changes in past centuries.
--- Slut citat ---


--- Citera ---"The long-term hemispheric trend is best described as a modest and irregular cooling from AD 1000 to around 1850 to 1900, followed by an abrupt 20th century warming. Regional evidence is, however, quite variable. Crowley and Lowery (2000) show that western Greenland exhibited anomalous warmth locally only around AD 1000 (and to a lesser extent, around AD 1400), with quite cold conditions during the latter part of the 11th century, while Scandinavian summer temperatures appeared relatively warm only during the 11th and early 12th centuries. Crowley and Lowery (2000) find no evidence for warmth in the tropics. Regional evidence for medieval warmth elsewhere in the Northern Hemisphere is so variable that eastern, yet not western, China appears to have been warm by 20th century standards from the 9th to 13th centuries. The 12th and 14th centuries appear to have been mainly cold in China (Wang et al., 1998a,b; Wang and Gong, 2000). The restricted evidence from the Southern Hemisphere, e.g., the Tasmanian tree-ring temperature reconstruction of Cook et al. (1999), shows no evidence for a distinct Medieval Warm Period."
--- Slut citat ---


--- Citera ---Mann et al. (1998) and Jones et al. (1998) support the idea that the 15th to 19th centuries were the coldest of the millennium over the Northern Hemisphere overall. However, viewed hemispherically, the "Little Ice Age" can only be considered as a modest cooling of the Northern Hemisphere during this period of less than 1°C relative to late 20th century levels (Bradley and Jones, 1993; Jones et al., 1998; Mann et al., 1998; 1999; Crowley and Lowery, 2000). Cold conditions appear, however, to have been considerably more pronounced in particular regions. Such regional variability can be understood in part as reflecting accompanying changes in atmospheric circulation. The "Little Ice Age" appears to have been most clearly expressed in the North Atlantic region as altered patterns of atmospheric circulation (O'Brien et al., 1995). 
--- Slut citat ---

http://www.grida.no/publications/other/ipcc_tar/?src=/climate/ipcc_tar/wg1/070.htm

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