Biological and Environmental Research - Earth and Environmental System Sciences
Earth and Environmental System Modeling

Fingerprints of external forcings on Sahel rainfall: aerosols, greenhouse gases, and model-observation discrepancies

TitleFingerprints of external forcings on Sahel rainfall: aerosols, greenhouse gases, and model-observation discrepancies
Publication TypeJournal Article
Year of Publication2020
JournalEnvironmental Research Letters
Volume15
Number8
Pages084023
Abstract / Summary

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 20th century and a detectable signal of greenhouse gas forcing at the beginning of the 21st. 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.

URLhttp://dx.doi.org/10.1088/1748-9326/ab858e
DOI10.1088/1748-9326/ab858e
Journal: Environmental Research Letters
Year of Publication: 2020
Volume: 15
Number: 8
Pages: 084023
Publication Date: 08/2020

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 20th century and a detectable signal of greenhouse gas forcing at the beginning of the 21st. 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.

DOI: 10.1088/1748-9326/ab858e
Citation:
Marvel, K, M Biasutti, and C Bonfils.  2020.  "Fingerprints of external forcings on Sahel rainfall: aerosols, greenhouse gases, and model-observation discrepancies."  Environmental Research Letters 15(8): 084023.  https://doi.org/10.1088/1748-9326/ab858e.