| Summary: | Paleoclimate records show that abrupt climate changes have occurred frequently in the past. Glacial inceptions, marking the end of interglacial periods, are always marked by sudden cooling events and increased millennial variability. The mechanisms responsible for these abrupt changes are uncertain, and are usually ascribed to interactions between atmosphere, ocean and ice sheets. The role of external forcing by changes in Earth’s orbit is untested. We conducted LOVECLIM transient climate simulations for interglacials of the last 800,000 years, and found that there exists a threshold in insolation that can trigger abrupt oscillations in the Atlantic meridional overturning circulation (AMOC) via sea ice-temperature feedbacks in the northern North Atlantic as well as atmospheric and oceanic teleconnections. This, in turn, leads to abrupt oscillations in other components of the climate system such as temperature, precipitation and vegetation at global scale. In particular, it causes abrupt and nearly anti-phased climate variability in Northern and Southern Hemispheres on centennial-millennial time scales. Our simulated results are supported by observations from ice and marine sediment cores. The proposed insolation threshold occurred repeatedly in the past especially at the end of interglacials, suggesting its fundamental role in ending interglacial conditions and initiating glacial inceptions. Using an ice sheet model, we further investigate the response and feedbacks of the Northern Hemisphere continental ice sheets to the abrupt climate oscillations.
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