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Science 23 July 1999:
Vol. 285. no. 5427, pp. 503 - 505
DOI: 10.1126/science.285.5427.503
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News of the Week

PALEOCLIMATE:
Why the Ice Ages Don't Keep Time

Richard A. Kerr

The ice ages and other recent climate change should come and go with clocklike regularity, or so the astronomical theory that links these changes to variations in Earth's orbit and spin axis implies. But the ice ages don't quite keep time, raising doubts about how much the astronomical theory can explain. Now, on page 564, a geophysicist explains why the timing of the ice ages seems to be off by invoking an interaction between orbital forcings that resembles the way FM radio signals are generated. And on page 568, researchers present a new record of the start of the ice ages 2.75 million years ago that ties them to an intensification of one orbital cycle.

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Science. ISSN 0036-8075 (print), 1095-9203 (online)