“Africa’s “Great Green Wall” initiative is a proposed 8,000-kilometer line of trees meant to hold back the Sahara from expanding southward. New climate simulations looking to both the region’s past and future suggest this greening could have a profound effect on the climate of northern Africa, and even beyond. … Previous studies have shown that a “green Sahara” is linked to changes in the intensity and location of the West African monsoon. That major wind system blows hot, dry air southwestward across northern Africa during the cooler months and brings slightly wetter conditions northeastward during the hotter months.”