THE ASTRONOMICAL THEORY in relationship to THE BEGINNING AND END OF OUR INTERGLACIAL
As our present interglacial, the Holocene, is already almost 12 kyr long, paleoclimatologists were inclined to predict a quite close entrance into the next ice age. Simulations using the climate model of Louvain-la-Neuve show however that our interglacial will most probably last much longer than any previous one, even without human intervention. This is related to the shape of the Earth’s orbit around the Sun which will be almost circular over the next tens of thousands of years, a situation which will give more weight to the other forcings, in particular to the forcing by the greenhouse gases. Our results show also that there is a threshold in the greenhouse gas concentration of about 700 ppmv beyond which the Greenland ice sheet melts in about 5000 years and does not recover before a few tens of thousands of years.
As the eccentricity variation is primarily related to the 400-kyr cycle, the best and closer analogue for such a forcing is definitively Marine isotopic Stage 11 (MIS-11) some 400 kyr ago. Simulations of this MIS-11 interglacial under greenhouse gas and astronomical forcings led indeed also to an anomalous length, a prediction which was later confirmed by the EPICA ice-core record. Such a relationship between CO2 and climate is at the basis of the claim by Ruddiman (2003) that the impact of human activities on climate might have already started 10,000 years ago, preventing our climate to have already entered into glaciation. Sensitivity experiments with the LLN model tend to rule out Ruddiman's hypothesis because glacial inception in this model would require CO2 concentration below 240 ppmv during the Holocene.
Curriculum vitae
André Berger is Emeritus Professor and Senior research Fellow of the Université catholique de Louvain. He is membre associé étranger de l’Académie des Sciences de Paris, membre de l’Académie royale des Sciences, des Lettres et des Beaux Arts de Belgique, foreign member of the Koninklijke Nederlandse Akademie van Wetenschappen and Honorary President of the European Geo-Sciences Union. He is a member of the Scientific Committee of the European Environment Agency. He received the European Latsis Prize of the European Science Foundation in 2001.