Africa’s central Sahel region has experienced prolonged drought
conditions in the past, while rainfall has recovered more recently.
Global climate models project anything from no change to a strong
wetting trend under unabated climate change; and they have difficulty
reproducing the complex historical record. Here we show that when a
period of dominant aerosol forcing is excluded, a consistent wetting
response to greenhouse-gas induced warming emerges in observed rainfall.
Using the observed response coefficient estimate as a constraint, we
find that CMIP6 climate models with a realistic past rainfall response
show a smaller spread, and higher median, of projected future rainfall
change, compared to the full ensemble. In particular, very small or
negative rainfall trends are absent from the constrained ensemble. Our
results provide further evidence for a robust Sahel rainfall increase in
response to greenhouse-gas forcing, consistent with recent observations,
and including the possibility of a very strong increase.