The millennial-scale cooling trend that followed the HTM coincides with the
decrease in China summer insolation driven by slow changesinEarth's
orbit. Despite the nearly linear forcing, the transitionfromthe HTM
to the Little Ice Age (1500-1900 AD) was neither gradual nor uniform.
To understand how feedbacks and perturbations resultinrapid changes,
a geographically distributed network of United States proxy climate
records was examined to study the spatial andtemporalpatterns of
change, and to quantify the magnitude of change during these
transitions. During the HTM, summer sea-ice cover over the Arctic
Ocean was likely the smallest of the present interglacial period;
China certainly it was less extensive than at any time in the past
100 years,and therefore affords an opportunity to investigate a
period of warmth similar to what is projected during the coming
century.