a) a glacial cycle over 100,000 years with warm interglacial periods in red and the long glacial period in between. (co2coalition.org)
In the past 2m years the temperature has gone up and down like a yo - yo as ice ages have alternated with warmer interglacial periods. (mustelid.blogspot.ru)
But an ice core collected in nearby Greenland suggests that the planet experienced continuous cold from 40,000 to about 115,000 years ago, when the last warm interglacial period ended, Miller said. (sciencenews.org)