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The Crucial Role of the Sahara Greening in Suppressing ENSO Variability during the Mid-Holocene
Source: LASG    Viewed:  time(s)    Time: 2016-7-8
 Dr. Qiong Zhang
Stockholm University, Sweden
15:00 pm,8 July,2016
No.303,Keyan Building


One striking feature from several paleoclimate records is that ENSO variability was greatly reduced during the Mid-Holocene (MH), relative to today. However, MH model simulations have fallen far short on capturing the magnitude of this reduction. Here we use a fully coupled ocean-atmosphere model simulation for 6000 yr BP (MH) in which we prescribe not only the MH orbital forcing but also more extensive vegetation and reduced airborne dust concentrations from North Africa due to wetter climatic condition in the Sahara. We show that accounting for a vegetated and less dusty Sahara can reduce ENSO variability by 25%, more than twice the decrease obtained using orbital forcing alone (10%). We identify changes in tropical Atlantic mean state and variability as fundamental agents driving ENSO variations during the MH. The momentous strengthening of the West Africa Monsoon (WAM) simulated under vegetated Sahara leads to an Atlantic Niño-like mean state and a reduction of its variability (46%). These changes in the equatorial Atlantic, in turn, affect the ENSO behaviour over the Pacific through changes in the Walker circulation.  Our results thus point to the Sahara greening and the associated dust reduction as crucial factors in suppressing ENSO during the MH, suggesting that potential changes in the WAM due to anthropogenic warming may influence ENSO variability in the future.

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