What turns ice ages on and off? ‘The Ice Age cometh’ considers the potential impact global warming may have on the arrival of the next expected Ice Age. Will global warming fend it off or will it accelerate the onset of the next big freeze? Conditions on Earth during the great freezes of the Cryogenian and the most recent Quaternary ice ages are described and what triggers them considered, including the Croll–Milankovitch astronomical theory. The Little Ice Age (c.ad 1450–1850) and the Medieval Warm Period (c.ad 1000–1300) are discussed along with the role ocean circulation (especially the Atlantic Meridional Overturning Circulation) has to play.