Mid-Holocene El Niño Southern Oscillation variability reduced by northern African vegetation changes in climate models

Several paleoclimatic reconstructions have indicated that the mid-Holocene (6,000 years before present) was characterized by stronger east-west temperature contrast and lower El Niño Southern Oscillation (ENSO) variability relative to the present day. While climate models show a reduction in ENSO variability, they underestimate this reduction compared to paleoclimate reconstructions. Further, the drivers behind these changes remain unclear. Here we use five global climate models to show that incorporating vegetation changes over northern Africa during the mid-Holocene amplifies the orbitally-driven strengthening of the West African Monsoon, warms the tropical north Atlantic, and nudges it to an Atlantic Niño-like mean state. Changes over the Atlantic lead to a La Niña-like mean state over the tropical Pacific, with reductions in interannual variability amplified by up to 18% in the Niño3.4 region due to the Green Sahara alone. Our work highlights the importance of the Atlantic influence on ENSO and provides paleoclimatic evidence for this synergistic teleconnection. Incorporating mid-Holocene vegetation changes over northern Africa amplifies Atlantic-driven teleconnections that shift the tropical Pacific toward a La Niña-like mean state and reduce El Niño-Southern Oscillation variability by up to 18%, according to simulations using global climate models.