The Greening of the Sahara: Past Changes and Future Implications

In the future, the Sahara and Sahelian regions could experience more rainfall than today as a result of climate change. Wetter periods, termed African humid periods, occurred in the past and witnessed a mesic landscape in place of today’s hyperarid and semiarid environment. Such large past changes raise the question of whether the near future might hold in store similar environmental transformations, particularly in view of the growing human-induced climate, land-use, and land-cover changes. In the last decades, geoengineering initiatives (in the form of active re-greening projects of the Sahara and Sahel) have been proposed and could have significant effects on the climate of the region. Here, we synthesize the literature on past and projected changes in the hydroclimate of the Sahelian-Saharan region and the associated feedbacks. We further address the current state of knowledge concerning Saharan and Sahelian afforestation projects and their consequences. Our review underscores the importance of vegetation in land-atmosphere-ocean feedback processes and the far-field impacts of northern African ecosystem changes.