Session: Warm Climates (Mid-Holocene, Last interglacial, Deep-time, Pliocene)
Author: Pausata Francesco S.R. / email@example.com / 1Department of Earth and Atmospheric Sciences, University of Quebec in Montreal (UQÀM), Montreal (QC), Canada
Co-author: Qiong Zhang, Department of Physical Geography, Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden;
Understanding the West African monsoon (WAM) dynamics in the mid-Holocene (MH) is a crucial issue in climate modelling, because climate models typically fail to reproduce the extensive precipitation suggested by proxy evidence. We show that this discrepancy may be largely due to the assumption of both unrealistic land surface cover and airborne dust concentration, which strongly feed back into the WAM strength. However, the climate response associated to the greening of the Sahara are not limited to North Africa but affect the entire globe: the ENSO activity and mean state is significantly altered, the tropical cyclone activity is enhanced in both hemisphere in particular over the Caribbean Sea and Gulf of Mexico, the Indian Summer Monsoon is intensified, the East Asian Monsoon shifts northward and the extra-tropical is also altered. Compared to the case in which only orbital forcing are considered, all these climate responses under a green Sahara condition have better agreement with the mid-Holocene climate indicated by paleo-proxy records.
Sensitivity experiments from a fully coupled ocean-atmosphere model EC-Earth show that the strengthening of the WAM induced by the orbital changes and amplified by the greening of the Sahara, shift and strengthen the Walker circulation, which triggers a chain of events that are responsible for the above-mentioned changes.