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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 18, issue 16 | Copyright
Atmos. Chem. Phys., 18, 12461-12475, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 28 Aug 2018

Research article | 28 Aug 2018

Connecting regional aerosol emissions reductions to local and remote precipitation responses

Daniel M. Westervelt1,2, Andrew J. Conley3, Arlene M. Fiore1,4, Jean-François Lamarque3, Drew T. Shindell5, Michael Previdi1, Nora R. Mascioli1,4, Greg Faluvegi2,6, Gustavo Correa1, and Larry W. Horowitz7 Daniel M. Westervelt et al.
  • 1Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York, USA
  • 2NASA Goddard Institute for Space Studies, New York, New York, USA
  • 3National Center for Atmospheric Research, Boulder, Colorado, USA
  • 4Department of Earth and Environmental Sciences, Columbia University, Palisades, New York, USA
  • 5Nicholas School of the Environment, Duke University. Durham, North Carolina, USA
  • 6Center for Climate Systems Research, Columbia University, New York, New York, USA
  • 7National Oceanic and Atmospheric Administration, Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey, USA

Abstract. The unintended climatic implications of aerosol and precursor emission reductions implemented to protect public health are poorly understood. We investigate the precipitation response to regional changes in aerosol emissions using three coupled chemistry–climate models: NOAA Geophysical Fluid Dynamics Laboratory Coupled Model 3 (GFDL-CM3), NCAR Community Earth System Model (CESM1), and NASA Goddard Institute for Space Studies ModelE2 (GISS-E2). Our approach contrasts a long present-day control simulation from each model (up to 400 years with perpetual year 2000 or 2005 emissions) with 14 individual aerosol emissions perturbation simulations (160–240 years each). We perturb emissions of sulfur dioxide and/or carbonaceous aerosol within six world regions and assess the significance of precipitation responses relative to internal variability determined by the control simulation and across the models. Global and regional precipitation mostly increases when we reduce regional aerosol emissions in the models, with the strongest responses occurring for sulfur dioxide emissions reductions from Europe and the United States. Precipitation responses to aerosol emissions reductions are largest in the tropics and project onto the El Niño–Southern Oscillation (ENSO). Regressing precipitation onto an Indo-Pacific zonal sea level pressure gradient index (a proxy for ENSO) indicates that the ENSO component of the precipitation response to regional aerosol removal can be as large as 20% of the total simulated response. Precipitation increases in the Sahel in response to aerosol reductions in remote regions because an anomalous interhemispheric temperature gradient alters the position of the Intertropical Convergence Zone (ITCZ). This mechanism holds across multiple aerosol reduction simulations and models.

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Small particles in Earth's atmosphere (also referred to as atmospheric aerosols) emitted by human activities impact Earth's climate in complex ways and play an important role in Earth's water cycle. We use a climate modeling approach and find that aerosols from the United States and Europe can have substantial effects on rainfall in far-away regions such as Africa's Sahel or the Mediterranean. Air pollution controls in these regions may help reduce the likelihood and severity of Sahel drought.
Small particles in Earth's atmosphere (also referred to as atmospheric aerosols) emitted by...