| Summary: | Understanding how and why global climate is changing is investigated at the astronomical time scale related to the glacial-interglacial cycles of the Quaternary Ice Age.A 2-dimensional physical model taking into account the coupling between the atmosphere, the upper ocean, the sea-ice, the ice-sheets and the continental surfaces has been forced by the long-term variations of the insolation induced by the astronomical changes in the elements of the Earth’s orbit. The low frequency part of the ice volume and sea-level changes have been correctly reproduced in agreement with the deep sea and ice cores records and with the climatic reconstructions made from multiple geological observations. However, after 6 kyr BP, the remaining ice volume of the Greenland and northern American ice sheets is overestimated in the simulation, probably because of the absence of an interactive carbon cycle providing a time-dependent atmospheric CO2 concentration.Extrapolation has been made for the next 100,000 years assuming no human interference at this time scale: the next ice age is expected to occur before 60,000 years AP, the cooling rate between now and then being roughly 0.01 °C per century. The maximum amount of ice to be expected in the northern hemisphere is 27*106 km3 representing a 70 m sea-level drop in 55,000 years, i.e. slightly more than 12 cm per century in average.
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