How North Atlantic aerosols steered Sahel rain
Fixing aerosols at 1920 levels removes the observed multidecadal Sahel drought–recovery cycle that tracks North Atlantic SST.
Source
Anthropogenic Aerosols Modulated 20th-Century Sahel Rainfall Variability Via Their Impacts on North Atlantic Sea Surface Temperature
What they did
Authors compared CESM1 large-ensemble all-forcing, aerosol-fixed, and GHG-fixed runs with CanESM2-LE, CMIP6, HadISST/NOAA SST, and CRU rainfall, linking sulfate, North Atlantic energy fluxes, SST, ITCZ, and Sahel rain.
What they found
Detrended NASST and Sahel rain share a 1925–1955 wet, 1955–1985 dry, then wet pattern that vanishes without evolving aerosols. NASST correlates with net surface energy (r=0.90) and sulfate burden (r=−0.82); aerosol–cloud interactions dominate the NASST effect.
The limits
What it doesn't show
Eight-model CMIP6 means do not fully kill internal variability; aerosol–cloud physics is the main model-spread source, so future Sahel rain still hinges on uncertain ACI.
Key terms
- NASST
- North Atlantic sea surface temperature.
- XAER
- Experiment with industrial aerosol emissions fixed at 1920.
- AMV
- Atlantic Multidecadal Variability of North Atlantic SST.
- ITCZ
- Intertropical Convergence Zone whose latitude sets Sahel monsoon rain.
- Aerosol–cloud interactions
- Indirect aerosol effects on clouds that dominate the modeled NASST signal.
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Quiz yourself
XAER experiment holds:
Common questions
Does the drought–recovery cycle appear without aerosol change?
No—it is absent in XAER ensemble means.
What ocean region mediates the effect?
North Atlantic SST and the ITCZ.
Sulfate vs NASST correlation?
r = −0.82 (p < 0.01).
Which aerosol process dominates?
Aerosol–cloud interactions (~two thirds).
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