Ice Age is a glacial episode during a past geological period. Global warming due to fossil fuels may be catastrophic in many ways, but will probably not much affect these longer-term cycles. We will have run out of fossil fuels long before the duration of a typical interglacial. Fluctuations in the amount of insolation (incoming solar radiation) are the most likely cause of large-scale changes in Earth’s climate during the Quaternary. In other words, variations in the intensity and timing of heat from the sun are the most likely cause of the glacial/interglacial cycles.