Saturday, 24 June 2017

Rapid ice sheet melting and the Sahelian population vulnerability

Source: "Consequences of rapid ice sheet melting on the Sahelian population vulnerability", PNAS 2017 114 (25) 6533-6538; published ahead of print June 5, 2017, [(PNAS (Proceedings of the National Academy of Sciences of the United States of America)]


Dimitri Defrancea,b,1, Gilles Ramsteina, Sylvie Charbita, Mathieu Vraca, Adjoua Moïse Famienb,c,, Benjamin Sultanb, Didier Swingedouwd, Christophe Dumasa, François Gemennee,f,, Jorge Alvarez-Solasg, and Jean-Paul Vanderlindene

Laboratoire des Sciences du Climat et de l'Environnement, Institut Pierre Simon Laplace, Commissariat à l'Energie Atomique et aux Energies Alternatives - CNRS - Université de Saint-Quentin-en-Yvelines, Université Paris-Saclay, 91141 Gif-Sur-Yvette, France;
Université Pierre et Marie Curie - CNRS - Institut de Recherche pour le Développement - Muséum National d'Histoire Naturelle, Laboratoire d'Océanographie et du Climat: Expérimentations et Approches Numériques, Institut Pierre Simon Laplace, 75005 Paris, France;
Laboratoire de Physique de l'Atmosphère, Université Félix Houphouet Boigny, 22 BP 582 Abidjan, Côte-d’Ivoire;
Environnements et Paléoenvironnements Océaniques et Continentaux, CNRS, Université de Bordeaux, 33615 Pessac, France;
Cultures Environnements Arctique Représentations Climat, Observatoire de Saint-Quentin-En-Yvelines, Université Paris-Saclay, 78280 Guyancourt, France;
The Hugo Observatory, Fonds de la Recherche Scientifique, University of Liège, 4000 Liège, Belgium;
PalMA Group, Universidad Complutense de Madrid, 28040 Madrid, Spain

Edited by Anders Levermann, Potsdam Institute for Climate Impact Research, Potsdam, Germany, and accepted by Editorial Board Member Hans J. Schellnhuber May 11, 2017 (received for review December 3, 2016)


A major uncertainty concerning the 21st century climate is the ice sheet response to global warming. Paleodata indicate rapid ice sheet destabilizations during the last deglaciation, which could lead to an underestimation of sea level rise, as suggested in recent publications. Therefore, we explore the impact of different scenarios of Greenland partial melting in the very sensitive Sahel region. We first demonstrate that such a melting induces a drastic decrease of West African monsoon precipitation. Moreover, we quantify the agricultural area losses due to monsoon changes. Consequently, we pinpoint a large potential for migration of millions of people in the coming decades. Thus, the ice sheet destabilization provokes not only coastal damages but also large population migration in monsoon area.


The acceleration of ice sheet melting has been observed over the last few decades. Recent observations and modeling studies have suggested that the ice sheet contribution to future sea level rise could have been underestimated in the latest Intergovernmental Panel on Climate Change report. The ensuing freshwater discharge coming from ice sheets could have significant impacts on global climate, and especially on the vulnerable tropical areas. During the last glacial/deglacial period, megadrought episodes were observed in the Sahel region at the time of massive iceberg surges, leading to large freshwater discharges. In the future, such episodes have the potential to induce a drastic destabilization of the Sahelian agroecosystem. Using a climate modeling approach, we investigate this issue by superimposing on the Representative Concentration Pathways 8.5 (RCP8.5) baseline experiment a Greenland flash melting scenario corresponding to an additional sea level rise ranging from 0.5 m to 3 m. Our model response to freshwater discharge coming from Greenland melting reveals a significant decrease of the West African monsoon rainfall, leading to changes in agricultural practices. Combined with a strong population increase, described by different demography projections, important human migration flows could be potentially induced. We estimate that, without any adaptation measures, tens to hundreds million people could be forced to leave the Sahel by the end of this century. On top of this quantification, the sea level rise impact over coastal areas has to be superimposed, implying that the Sahel population could be strongly at threat in case of rapid Greenland melting.