Examining the relative effects of obliquity and precession on variables important for glacial inception in Scandinavia and Baffin Island using linear reconstructions

Glacial cycles are driven by cyclical changes in Earth’s three orbital parameters: obliquity, precession, and eccentricity.  A common interpretation of Milankovitch’s orbital theory suggests that June insolation at 65°N is the dominant forcing in driving glacial cycles. This places emphasis on precession which has the greatest effect on June insolation at 65°N. However, there is abundant evidence for the importance of obliquity in driving glacial cycles. We compare the relative strengths of obliquity and precession on climate to further explore the possibility that obliquity could be more important than common interpretations of Milankovitch’s orbital theory would suggest. We use a set of coupled atmosphere-ocean general circulation model simulations to produce time series of key climate variables. Such variables include snowfall and positive degree-days (the sum of mean daily temperature for all days above 0°C), which are proxies for accumulation and ablation, respectively. We focus our analysis on glacial inception in Scandinavia and Baffin Island, the locations where the Scandinavian and Laurentide ice sheets were initiated. We show that obliquity causes changes in positive degree-days of larger magnitude than those of precession in both Scandinavia and Baffin Island. Snowfall is dominated by obliquity in Scandinavia and by precession in Baffin Island. The location dependence of the importance of obliquity and precession may have implications for deglaciation which occurred at lower latitudes than the inception locations. Additionally, our positive degree-day time series were most closely represented by Milankovitch’s caloric summer insolation metric than June insolation at 65°N.