Greening the Sahel : implications for climate change impact at regional and global scale

Séminaire de Marco GAETANI (LATMOS-IPSL), jeudi 14 mars à 11h, salle Lliboutry, bâtiment de Glaciologie

Abstract : Climate in West Africa is dominated by the dynamics of the West African monsoon (WAM), which drives precipitation to the region during boreal summer. WAM dynamics plays a key role in determining regional climate impacts, affecting crop productivity, human health and infrastructure security. WAM dynamics also affects climate in remote areas, by modulating the tropical cyclone activity in the Atlantic and the dust emission and transport from the Sahel.
In West Africa, climate variability is particularly pronounced, and drove dramatic environmental changes in the past. During mid Holocene, 6k years ago, resulting from the effect of different orbital parameters on the Earth’s radiative budget, precipitation was more abundant and Sahara was vegetated. The feedback from vegetation cover and the consequent reduced airborne dust was crucial in sustaining the strengthening of the WAM, as well as in the rapid desertification of the region, when the orbital parameters returned to present-day values. During the 20th century, in response to the anthropogenic Global Warming, WAM precipitation was characterised by a negative trend which resulted in a devastating drought that affected the Sahel in the 80s. Interestingly, at local scale atmospheric CO2 favours monsoonal precipitation, by both enhancing warming at the surface and triggering evaporation and vertical instability, and fertilising vegetation. As a consequence, future climate projections respond to the increasing CO2 radiative forcing with a widespread intense warming in West Africa, whereas there is no unanimity on future precipitation trends. The combination of high climate sensitivity, complex climate dynamics and climate vulnerability makes West Africa a climate change hotspot, and further efforts are demanded to the climate science community in the quest for reliable and usable climate predictions.
In this seminar, the role of vegetation and airborne dust feedback on climate dynamics and impacts in West Africa and in remotely connected regions is discussed, in the perspective of global increasing CO2 atmospheric concentration and possible future greening of the Sahel.

By Marco Gaetani, LATMOS-IPSL