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

Marvel, Kate; Biasutti, Michela; Bonfils, Céline

doi:10.1088/1748-9326/ab858e

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

Journal Article · Thu Jul 30 00:00:00 EDT 2020 · Environmental Research Letters

DOI:https://doi.org/10.1088/1748-9326/ab858e· OSTI ID:1769075

Marvel, Kate ^[1]; Biasutti, Michela ^[2]; Bonfils, Céline ^[3]

NASA Goddard Inst. for Space Studies (GISS), New York, NY (United States); Columbia Univ., New York, NY (United States)
Columbia Univ., New York, NY (United States)
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

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.

View Accepted Manuscript (DOE)

Research Organization:: Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)

Sponsoring Organization:: USDOE National Nuclear Security Administration (NNSA); USDOE Office of Science (SC), Biological and Environmental Research (BER)

Grant/Contract Number:: AC52-07NA27344; SC0014423

OSTI ID:: 1769075

Alternate ID(s):: OSTI ID: 23048887

Report Number(s):: LLNL-JRNL--804675; 1008184

Journal Information:: Environmental Research Letters, Journal Name: Environmental Research Letters Journal Issue: 8 Vol. 15; ISSN 1748-9326

Publisher:: IOP PublishingCopyright Statement

Country of Publication:: United States

Language:: English

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