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A sea surface temperature (SST) record based on planktonic foraminiferal magnesium/calcium ratios from a site in the western equatorial Pacific warm pool reveals that glacial-interglacial oscillations in SST shifted from a period of 41,000 to 100,000 years at the mid-Pleistocene transition, 950,000 years before the present. SST changes at both periodicities were synchronous with eastern Pacific cold-tongue SSTs but preceded changes in continental ice volume. The timing and nature of tropical Pacific SST changes over the mid-Pleistocene transition implicate a shift in the periodicity of radiative forcing by atmospheric carbon dioxide as the cause of the switch in climate periodicities at this time. [ABSTRACT FROM AUTHOR]

Introduces a report by Jose Rial, in this issue, that explains why the timing of the ice ages seems to off by invoking an interaction between orbital forcings that resemble the way FM radio signals are generated. Comments on the Milankovich theory, which suggests that ice ages and much other climate changes should unfold with clocklike precision; Report by Katherine Willis, in the same issue, that presents a new record of the start of the ice ages and suggests what triggered an abrupt drop in northern glaciation.

Discusses methods of measuring ice age temperatures. Importance of the measurements for general circulation models (GCM) and predictions of greenhouse warming; Difference between the last glacial maximum (LGM) and modern conditions; Temperature variability shown in high-resolution climate records for the last ice age; Process of documenting LGM climate; LGM temperature maps; Problems with LGM theories; Advances in paleodata.