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Mid-Holocene ENSO Variability reduced by northern African vegetation changes: a model intercomparison study
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  • Shivangi Tiwari,
  • Francesco S.R. Pausata,
  • Allegra N. LeGrande,
  • Michael Griffiths,
  • ILana Wainer,
  • Hugo Beltrami,
  • Anne de Vernal,
  • Peter O. Hopcroft,
  • Clay R Tabor,
  • Deepak Chandan,
  • W. Richard Peltier
Shivangi Tiwari
Universite du Quebec a Montreal

Corresponding Author:[email protected]

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Francesco S.R. Pausata
University of Quebec in Montreal
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Allegra N. LeGrande
NASA GISS
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Michael Griffiths
William Paterson University
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ILana Wainer
Universidade de Sao Paulo
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Hugo Beltrami
St. Francis Xavier University
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Anne de Vernal
GEOTOP-UQAM
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Peter O. Hopcroft
University of Birmingham
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Clay R Tabor
University of Connecticut
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Deepak Chandan
University of Toronto
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W. Richard Peltier
Department of Physics, University of Toronto
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Abstract

The relationship between the mean state of the Pacific Ocean and El Niño Southern Oscillation (ENSO) and its variability through time is inadequately understood, especially on longer timescales. Several studies have indicated that the mid-Holocene (6,000 years before present) was characterized by stronger east-west temperature contrast and lower ENSO variability relative to the present day. While climate models show a reduction in ENSO variability, they underestimate this reduction compared to many paleoclimate reconstructions. Further, the drivers behind these changes remain unclear. In this work, we use five global climate models to show that incorporating vegetation changes over northern Africa during the mid-Holocene are vital to capturing global circulation changes. Greening the Sahara alters the Walker Circulation, enhancing zonal temperature and pressure gradients in the equatorial Pacific and driving it to a La Niña-like state. Incorporating Green Sahara boundary conditions leads to reductions in interannual variability in all Niño index regions relative to orbital and GHG changes, with reductions of up to 18% in the Niño3.4 region. Our work highlights the importance of the Atlantic influence on ENSO and provides paleoclimatic evidence for this synergistic teleconnection.
02 Oct 2024Submitted to ESS Open Archive
03 Oct 2024Published in ESS Open Archive