Articles | Volume 17, issue 19
Atmos. Chem. Phys., 17, 12197–12218, 2017
Atmos. Chem. Phys., 17, 12197–12218, 2017
Research article
13 Oct 2017
Research article | 13 Oct 2017

Aerosols at the poles: an AeroCom Phase II multi-model evaluation

Maria Sand1,2, Bjørn H. Samset1, Yves Balkanski3, Susanne Bauer2, Nicolas Bellouin4, Terje K. Berntsen1,5, Huisheng Bian6, Mian Chin7, Thomas Diehl8, Richard Easter9, Steven J. Ghan9, Trond Iversen10, Alf Kirkevåg10, Jean-François Lamarque11, Guangxing Lin9, Xiaohong Liu12, Gan Luo13, Gunnar Myhre1, Twan van Noije14, Joyce E. Penner15, Michael Schulz10, Øyvind Seland10, Ragnhild B. Skeie1, Philip Stier16, Toshihiko Takemura17, Kostas Tsigaridis2, Fangqun Yu13, Kai Zhang18,9, and Hua Zhang19 Maria Sand et al.
  • 1Center for International Climate and Environmental Research – Oslo (CICERO), Oslo, Norway
  • 2NASA Goddard Institute for Space Studies and Columbia Earth Institute, New York, NY, USA
  • 3Laboratoire des Sciences du Climat et de l'Environnement, CEA-CNRS-UVSQ, Gif-sur-Yvette, France
  • 4Department of Meteorology, University of Reading, Reading, UK
  • 5Department of Geosciences, University of Oslo, Oslo, Norway
  • 6Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD, USA
  • 7NASA Goddard Space Flight Center, Greenbelt, MD, USA
  • 8Directorate for Sustainable Resources, Joint Research Centre, European Commission, Ispra, Italy
  • 9Pacific Northwest National Laboratory, Richland, WA, USA
  • 10Norwegian Meteorological Institute, Oslo, Norway
  • 11National Center for Atmospheric Research, Boulder, CO, USA
  • 12Department of Atmospheric Science, University of Wyoming, USA
  • 13Atmospheric Sciences Research Center, State University of New York at Albany, New York, USA
  • 14Royal Netherlands Meteorological Institute, De Bilt, the Netherlands
  • 15Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI, USA
  • 16Department of Physics, University of Oxford, Oxford, UK
  • 17Research Institute for Applied Mechanics, Kyushu University, Fukuoka, Japan
  • 18Max Planck Institute for Meteorology, Hamburg, Germany
  • 19Laboratory for Climate Studies, National Climate Center, China Meteorological Administration, Beijing, China

Abstract. Atmospheric aerosols from anthropogenic and natural sources reach the polar regions through long-range transport and affect the local radiation balance. Such transport is, however, poorly constrained in present-day global climate models, and few multi-model evaluations of polar anthropogenic aerosol radiative forcing exist. Here we compare the aerosol optical depth (AOD) at 550 nm from simulations with 16 global aerosol models from the AeroCom Phase II model intercomparison project with available observations at both poles. We show that the annual mean multi-model median is representative of the observations in Arctic, but that the intermodel spread is large. We also document the geographical distribution and seasonal cycle of the AOD for the individual aerosol species: black carbon (BC) from fossil fuel and biomass burning, sulfate, organic aerosols (OAs), dust, and sea-salt. For a subset of models that represent nitrate and secondary organic aerosols (SOAs), we document the role of these aerosols at high latitudes.

The seasonal dependence of natural and anthropogenic aerosols differs with natural aerosols peaking in winter (sea-salt) and spring (dust), whereas AOD from anthropogenic aerosols peaks in late spring and summer. The models produce a median annual mean AOD of 0.07 in the Arctic (defined here as north of 60° N). The models also predict a noteworthy aerosol transport to the Antarctic (south of 70° S) with a resulting AOD varying between 0.01 and 0.02. The models have estimated the shortwave anthropogenic radiative forcing contributions to the direct aerosol effect (DAE) associated with BC and OA from fossil fuel and biofuel (FF), sulfate, SOAs, nitrate, and biomass burning from BC and OA emissions combined. The Arctic modelled annual mean DAE is slightly negative (−0.12 W m−2), dominated by a positive BC FF DAE in spring and a negative sulfate DAE in summer. The Antarctic DAE is governed by BC FF. We perform sensitivity experiments with one of the AeroCom models (GISS modelE) to investigate how regional emissions of BC and sulfate and the lifetime of BC influence the Arctic and Antarctic AOD. A doubling of emissions in eastern Asia results in a 33 % increase in Arctic AOD of BC. A doubling of the BC lifetime results in a 39 % increase in Arctic AOD of BC. However, these radical changes still fall within the AeroCom model range.

Short summary
The role of aerosols in the changing polar climate is not well understood and the aerosols are poorly constrained in the models. In this study we have compared output from 16 different aerosol models with available observations at both poles. We show that the model median is representative of the observations, but the model spread is large. The Arctic direct aerosol radiative effect over the industrial area is positive during spring due to black carbon and negative during summer due to sulfate.
Final-revised paper