Fourier and nonlinear regression analysis of a 4000+ yr paleoclimate proxy record in western Canada shows strong periodicities of ∼1500 yr and several weaker century- to millenial-scale periodicities. In conjunction with the 23 708 yr Milankovitch periodicity, these produce a model of climate fluctuation through the postglacial consistent with recognized paleoclimatic fluctuations of the past 15 000 yr in the northern mid-latitudes. These results suggest that postglacial climatic anomalies such as the Little Ice Age and the Younger Dryas were at least in part periodic phenomena rather than the result of unique, aperiodic events. Projecting these periodicities into the future suggests that even in the absence of anthropogenic climate forcing, a natural warming trend will continue until ca. a.d. 2400.