Modeling studies suggest that the summer solstice solar radiation is more important than the caloric half-year solar radiation in producing glacial/interglacial cycles because it is more representative of the energy available to melt ice during the short melt season. Here it is shown that the correlation between the summer solstice solar radiation and the rate of change of the oxygen isotope record is generally greater than that between the caloric half-year radiation and the rate of change of the oxygen isotope record. These results also suggest that the sawtoothed nature of the 100 kyr cycle may be produced by periods of relatively slow changes in ice volume, punctuated by periods of rapid growth that are initiated at times of extremely low summer solstice radiation; and that it is unlikely that an ice age will begin in the next 70 kyr. ¿ American Geophysical Union 1995