Transcript gcc_talk
Evidence for the Jumping Jet Hypothesis of abrupt climate Change Evidence of Abrupt Climate Change- DO Events from GISP 2 Warmer TIME (Stuiverand and Grooves, Grooves, 2001) (Stuiver 2000) • At least 20 DO (Dansgaard-Oeschger) events recorded in the last 120 Kyears (Rahmstorf, 2003) • Rapid warming followed by slow cooling then rapid cooling Dust In Greenland During Abrupt Climate Change Warmer More Dust Time Cold times in Greenland are dustier (order of magnitude) Courtesy of Stephen Barker High resolution abrupt warming More Dust Less Dust Temperature Dust Warm 50 years Time Cold Dust changes are more abrupt and precede temperature changes Fuhrer, 1999 Scatter Plot of ice core oxygen isotope and calcium concentration More Dust Stadial (Cold) Data Points Interstadial (Warm) Data Warmer [Fuhrer,1999] Temperature (oxygen isotopes) overlap between regimes but calcium does not •CLIMATE REGIME IS BEST CHARACTERIZED BY ATMOSPHERC DUST LOAD – FACTOR OF 10 change Ideas that do NOT explain dust changes • Strength of Deposition- Wet deposition is dominant [Steffenson, 1997] • Change in source area- all dust is from Asia [Svenson, 2000] • Change in size of source area- Greenland change is too quick [Fuhrer, 1999] • Stronger winds- sea salts in core change moderately [Mogenson, 2002] Could the Laurentide Ice Sheet Cause the Jet Stream to Jump? Jet flows to the south of the topography- similar to the Modern day circulation Jet flows to the north of the topography Force A General Circulation Model with glacial conditions and two different ice sheets Courtesy Camille Li How does the atmospheric circulation change- Stationary waves How does the Atlantic Jet And storm track change? Small Ice Contours = Jet speed (m/s) At 300 hPa Colors = Storm activity (V’T’ at 700 hPa) Big Ice K m/s Back Trajectories from Greenland Small Ice Back Trajectories From Summit Big Ice Origin (15 days At 500 hPa) How sensitive is the transition in atmospheric circulation to the ice sheet topography? Courtesy Joe Barsugli Conclusions • The dust changes in Greenland during abrupt climate change are more rapid and precede the temperature changes • We speculate these changes indicate a change in the atmospheric circulation regime • A general circulation model shows that the Jet Stream may jump during the glacial in a way which may be consistent with the change in dust loading Courtesy Stephen Barker