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Multiple, Younger Dryas (YD) moraines in both the Northern and Southern Hemisphere imply that abrupt, short-lived, glacial fluctuations were the result of globally synchronous, climatic oscillations with no significant lag between hemispheres. The lack of a time lag between double YD moraines in the Northwestern U.S., Rocky Mts., Swiss Alps, Scandinavia, and New Zealand means that changes in the North Atlantic deep current cannot adequately explain the abrupt global Younger Dryas climate changes.
The Cordilleran Ice Sheet built well-dated, YD moraines in the northern Puget Lowland between 10 and 11 14C ka., similar to the classic, well-dated double YD moraines of the Scandinavian Ice Sheet. Double YD alpine moraines occur at Mt. Baker, Icicle Creek, and Mt. Rainier in the North Cascade Range, Washington, in the Sawtooth Range of the northern Rocky Mts., Idaho, in the Titcomb Basin and at Temple Lake in the Wind River Range, Wyoming, and at Julier Pass in the Swiss Alps. In the Southern Hemisphere, double YD alpine moraines occur at Arthur's Pass, Birch Hill, and Prospect Hills of New Zealand. In each of these areas, two or more YD moraines suggest that the YD was not only global, but that glaciers were sensitive enough to record at least two distinct phases within the YD. The double YD glacial chronology closely matches that of ice cores from Greenland and sea surface temperatures in the north Pacific.
The double nature of the abrupt, global, YD climate changes that caused synchronous readvances of both ice sheets and alpine glaciers in widely separated regions on several continents in both hemispheres indicates a common global cause. These synchronous, inter-hemispheric climatic oscillations cannot be explained by Milankovitch/Croll orbital forcing, North Atlantic thermohaline switches, or Laurentide ice-sheet surges. The world's glaciers clearly fluctuated in response to globally synchronous climate changes whose source was atmospheric.
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