McManus, J.F., Oppo, D.W. and Cullen, J.L. 1999. A 0.5-million-year record of millennial-scale climate variability in the North Atlantic. Science 283: 971-974.
What was done
The authors examined a half-million-year-old deep-sea sediment core in the eastern North Atlantic to infer changes in climate over the last five glacial-interglacial cycles.
What was learned
Significant temperature oscillations were noted throughout the record, but they were of much greater amplitude during glacial episodes. Sea-surface temperature, for example, oscillated between 1 to 2°C during warm interglacials, but varied between 4 to 6°C during colder glacial times.
What it means
In the words of the authors, climatic "variability on millennial time scales has thus been the rule, rather than the exception." Hence, it is likely that the warming of the last century or so has been a natural occurrence unrelated to the concurrent increase in atmospheric CO2.
This study also contradicts the notion that any future global warming will result in harsh climatic temperature extremes, as is often predicted by general circulation models; for the historical record clearly indicates less temperature variability during warmer time periods.
Reviewed 15 March 1999