loading page

Fingerprints of External Forcings on Sahel Rainfall: Aerosols, Greenhouse Gases, and Model-Observation Discrepancies
  • Kate Marvel,
  • Michela Biasutti,
  • Céline Bonfils
Kate Marvel
NASA GISS/Columbia University

Corresponding Author:[email protected]

Author Profile
Michela Biasutti
Lamont-Doherty Earth Observatory
Author Profile
Céline Bonfils
Author Profile


Over the 20th and 21st centuries, both anthropogenic greenhouse gas increases and changes in anthropogenic aerosols have affected rainfall in the Sahel. Using multiple characteristics of Sahel precipitation, we construct a multivariate fingerprint that allows us to distinguish between the model-predicted responses to greenhouse gases and anthropogenic aerosols. Models project the emergence of a detectable signal of aerosol forcing in the middle of the twentieth century and a detectable signal of greenhouse gas forcing at the beginning of the twenty-first. However, the signals of both aerosol and greenhouse gas forcing in observations emerge earlier and are stronger than in the models, far stronger in the case of aerosols. The similarity between the response to aerosol forcing and the leading mode of internal variability makes it difficult to attribute this model-observation discrepancy to errors in the forcing, errors in the forced response, model inability to capture the amplitude of internal variability, or some combination of these. For greenhouse gases, however, the forced response is distinct from internal variability as estimated by models, and the observations are largely commensurate with the model projections.
01 Aug 2020Published in Environmental Research Letters volume 15 issue 8 on pages 084023. 10.1088/1748-9326/ab858e