qIt is still not fully understood
what caused the millennial-scale climate changes.
qAny successful hypotheses have to explain
q (1) What initiated these
oscillations?
q (2) How are they
transmitted to various part of the climate system?
q (3) Why are they stronger
during glaciations than during interglaciations?
qThree possible hypotheses have been suggested:
q (1) The natural
oscillations inherent in the internal behavior of northern hemisphere ice sheets
q (2) The result of internal
interactions among subcomponents of the climate system
q (3) A response to solar
variations external to the climate system.