Green Sahara collapse drives Holocene cooling

Abstract

Understanding Holocene climate evolution is essential for gaining insights into natural climate variability and feedback mechanisms. Proxy records consistently indicate Early to Mid-Holocene warming followed by late cooling. However, most climate models simulate unidirectional warming throughout the Holocene, resulting in a persistent model–data discrepancy. To address this gap, we conducted Holocene transient simulations using the fully coupled Community Earth System Model (CESM1.2) with dynamic vegetation, complemented by an idealized supplementary “Green Sahara” (GS) experiment. In the GS scenario, Early to Mid-Holocene desert soil properties in the Sahara were replaced with those from adjacent non-desert regions to mimic enhanced land surface greening. Notably, the GS experiment simulated a Mid-Holocene global mean annual temperature anomaly of 0.28°C above preindustrial levels, as well as an approximately ninefold increase in in annual precipitation over the Sahara, both consistent with proxy reconstructions and independent geological evidence. We argue that the inability of previous simulations to reproduce Early to Mid-Holocene warming, due to insufficient consideration of vegetation–climate feedbacks, is a primary cause of the discrepancy between models and reconstructions. This study highlights that incorporating realistic vegetation and land surface changes is critical for accurately simulating Holocene climate evolution.