Remote Vegetation Feedbacks and the Mid-Holocene Green Sahara

Abstract

In the mid-Holocene, the climate of northern Africa was characterized by wetter conditions than present, as evidenced by higher paleolake levels and pollen assemblages of savannah vegetation suggesting a wetter, greener Sahara. Previous modeling studies have struggled to simulate sufficient amounts of precipitation when considering orbital forcing alone, with limited improvement from considering the effects of local grasslands. Here it is proposed that remote forcing from expanded forest cover in Eurasia relative to today is capable of shifting the intertropical convergence zone northward, resulting in an enhancement in precipitation over northern Africa approximately 6000 years ago greater than that resulting from orbital forcing and local vegetation alone. It is demonstrated that the remote and local forcing of atmospheric circulation by vegetation can lead to different dynamical patterns with consequences for precipitation across the globe. These ecoclimate teleconnections represent the linkages between the land surface in different regions of the globe and by inference show that proxy records of plant cover represent not only the response of vegetation to local climate but also that vegetation’s influence on global climate patterns.