In a new study published in Science, a team of scientists from the National Center for Atmospheric Research and eight universities in the United States and China drew on analyses of sediments and other records of past climate and transient simulations with the CCSM climate model. They found that when the model included the orbitally-forced insolation changes, increasing greenhouse gases, and retreating ice sheets and associated meltwater release to the oceans, the temporal evolution of the simulated deglacial precipitation showed good agreement with individual proxy records. The model simulation found that as the ice sheets that covered large parts of North America and northern Europe started retreating from their maximal extent, meltwater release into the northern North Atlantic Ocean reduced the Atlantic meridional overturning circulation (AMOC) to near shutdown and cooled the North Atlantic sea surface temperatures. Cooling over the North Atlantic was rapidly transmitted eastward into Europe and Asia and over the western Indian Ocean through the atmosphere. Simulated precipitation was suppressed in northern Africa and southeastern equatorial Africa.

Once the AMOC reestablished, wetter conditions developed rapidly in northern Africa and southeastern equatorial Africa. Wetter conditions developed north of the equator in response to high summer insolation associated with orbital cycles and increasing GHG concentrations, whereas wetter conditions south of the equator were a response primarily to the GHG increase.