The Antarctic Vostok ice core provided compelling evidence of the nature of climate,
and of climate feedbacks, over the past 420,000 years. Marine records suggest that
the amplitude of climate variability was smaller before that time, but such records
are often poorly resolved. Moreover, it is not possible to infer the abundance of
greenhouse gases in the atmosphere from marine records. Here we report the recovery
of a deep ice core from Dome C, Antarctica, that provides a climate record for the
past 740,000 years. For the four most recent glacial cycles, the data agree well with
the record from Vostok. The earlier period, between 740,000 and 430,000 years ago,
was characterized by less pronounced warmth in interglacial periods in Antarctica,
but a higher proportion of each cycle was spent in the warm mode. The transition from
glacial to interglacial conditions about 430,000 years ago (Termination V) resembles
the transition into the present interglacial period in terms of the magnitude of change
in temperatures and greenhouse gases, but there are significant differences in the
patterns of change. The interglacial stage following Termination V was exceptionally
long--28,000 years compared to, for example, the 12,000 years recorded so far in the
present interglacial period. Given the similarities between this earlier warm period
and today, our results may imply that without human intervention, a climate similar
to the present one would extend well into the future.