Groups and Networks

Human development has coincided with one of the relatively infrequent episodes of prolonged climate stability, of a little over 10 000 years since the end of the last glaciation. This episode is the latest of a series of interglacial phases which, in the last half million years, have occurred at intervals of roughly 100 000 years. It has been commonly thought that we are at the tail-end of this warm climate phase, and that feeling sharpened in the late 1990’s when new data from Antarctic ice cores showed that the previous three warm phases each lasted between 6000 and 9000 years. Thus, given a similar trend, the ice-sheets would have returned to cover Europe during the ancient Egyptian or Greek civilizations, and the trend of human history would have been immeasurably different.

This year, though, the longest Antarctic ice-core record yet obtained shows that the warm phase before that, a little less than half a million years ago, lasted some 30 000 years. That long interglacial episode is thought to be the best model for our current warm phase, because of the similarity of the earth’s alignment vis-à-vis the sun’s rays. On these grounds, therefore, even without human intervention, another 20 000 years of warmth may be expected.

Sources
Boreholes drilled though the Greenland and Antarctica ice-caps provide the most detailed picture of the timing of climate change over the last 700 000 years. Up until this year, the longest record was the 400 000 year Vostok core, described by:

• Petit, J.R. et al. 1999. Climate and atmospheric history of the past 420 000 years from the Vostok ice core, Antarctica. Nature, vol. 399, pp. 429-436.

The new, long ice core is still being studied; outline results are given in:

• EPICA community members. 2004. Eight glacial cycles from an Antarctic ice core. Nature, vol. 623, pp. 623-628 (also discussed on pp. 611-612 of the same issue).

The Greenland icecap does not provide such a long record as does Antarctica, but it provides an even finer-scale climate history: see for instance:

• North Greenland Ice Core Project members 2004. High-resolution record of Northern Hemisphere climate extending into the last interglacial period. Nature, vol. 431, pp. 147-151 (also discussed in pp. 133-134 of the same issue).
• See also Berger, A. & Loutre, M.F. 2002. An exceptionally long interglacial ahead? Science, vol. 297, pp. 1287-1288.