Climate changes are driven largely by variations in the distribution of solar insolation associated with changes in the Earth's orbital parameters. Here we define the rate of solar insolation change (RSIC) as a parameter to evaluate and quantify solar heating changes through time. We propose that RSIC may control the timing of transitions between warm and cold periods through its control on the rate of climate changes. Specifically, the glacial/interglacial transitions took place when the 65¿N July insolation experienced the most rapid changes; interglacials start with a maximum positive RSIC and end with a maximum negative RISC. The RSIC curve thus provides a new astronomically tuned method for dating interglacials. The 65¿N July RISC curves average a 4.7 ky lead compared to ice sheet changes as indicated by Bassinot et al. <1994> for the last 0.9 Ma, possibly implying a more rapid response of monsoonal climate to the insolation heating.