Lesson from the past: present insolation minimum holds potential for glacial inception

Abstract

The community of climatologists predicts a progressive global warming [IPCC Fourth Assessment Report—Climate Change, 2007. The Scientific Basis. Cambridge University Press, Cambridge] that will not be interrupted by a glacial inception for the next 50ka [Berger and Loutre, 2002. An exceptionally long Interglacial ahead? Science 297, 1287–1288]. These predictions are based on continuously increasing anthropogenic greenhouse gas emissions and on the orbital forcing that will provide only muted insolation variations for the next 50ka. To assess the potential climate development without human interference, we analyse climate proxy records from Europe and the North Atlantic of Marine Isotope Stage (MIS) 11 (423–362kaBP), an interval when insolation variations show a strong linear correlation with those of the recent past and the future. This analysis suggests that the insolation minimum at 397kaBP, which provides the best available analogue to the present insolation minimum, terminated interglacial conditions in Europe. At that time, tundra–steppe vegetation spread in Central Europe and pine forests dominated in the eastern Mediterranean region. Because the intensities of the 397kaBP and present insolation minima are very similar, we conclude that under natural boundary conditions the present insolation minimum holds the potential to terminate the Holocene interglacial. Our findings support the Ruddiman hypothesis [Ruddiman, W., 2003. The Anthropogenic Greenhouse Era began thousands of years ago. Climate Change 61, 261–293], which proposes that early anthropogenic greenhouse gas emission prevented the inception of a glacial that would otherwise already have started.