Abstract:
Greenland ice-core records provide an exceptionally clear picture of many
aspects of abrupt climate changes, and particularly of those associated with
the Younger Dryas event, as reviewed here. Well-preserved annual layers can be
counted confidently, with only 1% errors for the age of the end of the Younger
Dryas 11,500 years before present. Ice-flow corrections allow reconstruction
of snow
... accumulation rates over tens of thousands of years with little
additional uncertainty. Glaciochemical and particulate data record
atmospheric-loading changes with little uncertainty introduced by changes in
snow accumulation. Confident paleothermometry is provided by site-specific
calibrations using ice-isotopic ratios, borehole temperatures, and
gas-isotopic ratios. Near-simultaneous changes in ice-core paleoclimatic
indicators of local, regional, and more-widespread climate conditions
demonstrate that much of the Earth experienced abrupt climate changes
synchronous with Greenland within thirty years or less. Post-Younger Dryas
changes have not duplicated the size, extent and rapidity of these
paleoclimatic changes. 
