Why do glacial periods end abruptly?
Notice the asymmetric shape of the Dome Fuji temperature record, with abrupt warmings shown in yellow preceding more gradual coolings (Figure 3). Warming at the end of glacial periods tends to happen more abruptly than the increase in solar insolation. There are several positive feedbacks that are responsible for this. One is the ice-albedo feedback. A second feedback involves atmospheric CO2. Direct measurement of past CO2 trapped in ice core bubbles show that the amount of atmospheric CO2 decreased during glacial periods (Figure 3), in part because more CO2 was stored in the deep ocean due to changes in either ocean mixing or biological activity. Lower CO2 levels weakened the atmosphere’s greenhouse effect and helped to maintain low temperatures. Warming at the end of the glacial periods liberated CO2 from the ocean, which strengthened the atmosphere’s greenhouse effect and contributed to further warming.
