describes the collective effects of changes in the Earth's movements upon its climate[.]
By this theory, the Earth is now experiencing an interglacial.
By the theory, when will the interglacial end and the next ice age begin?
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This paper seems to be discussing what you've asked: http://www.sciencemag.org/content/297/5585/1287.full. The next ice age is expected to begin about 50,000 years from now. However, I think it's still debatable how accurate the predictions of Milankovitch cycles are, and how much of an effect humans are likely to have on this earth system.