qClimate changes of these scales in the past several tens of thousands of years
occurred within the time span of recorded human civilization.
qThese change can be resolved by 14C-dated records.
qThe major boundary conditions that have driven climate changes during the
last 21,000 years have been the changes in:
q (1) size of ice sheet
q (2) seasonal insolation
q (3) level of greenhouse gases in the atmosphere.