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Preprints
https://doi.org/10.5194/acp-2019-1203
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-1203
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 13 Jan 2020

Submitted as: research article | 13 Jan 2020

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This preprint is currently under review for the journal ACP.

Evaluation of climate model aerosol trends with ground-based observations over the last two decades – an AeroCom and CMIP6 analysis

Augustin Mortier1, Jonas Gliss1, Michael Schulz1, Wenche Aas2, Elisabeth Andrews3, Huisheng Bian4, Mian Chin5, Paul Ginoux6, Jenny Hand7, Brent Holben5, Zhang Hua8, Zak Kipling9, Alf Kirkevåg1, Paolo Laj10, Thibault Lurton11, Gunnar Myhre12, David Neubauer13, Dirk Olivié1, Knut von Salzen14, Toshihiko Takemura15, and Simon Tilmes16 Augustin Mortier et al.
  • 1Norwegian Meteorological Institute, Oslo, Norway
  • 2NILU, Norwegian Institute for Air Research, Kjeller, Norway
  • 3Cooperative Institute for Research in Environmental Sciences,University of Colorado, Boulder, Colorado, USA
  • 4Maryland Univ. Baltimore County (UMBC), Baltimore, MD, USA
  • 5NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
  • 6NOAA, Geophysical Fluid Dynamics Laboratory, Princeton, NJ, USA
  • 7Cooperative Institute for Research in the Atmosphere, Colorado State University, Fort Collins, CO, USA
  • 8Laboratory for Climate Studies, National Climate Center, China Meteorological Administration, Beijing, China
  • 9European Centre for Medium-Range Weather Forecasts, Reading, UK
  • 10Univ. Grenoble Alpes, CNRS, IRD, Grenoble INP, Institute for Geosciences and Environmental Research, Grenoble, France
  • 11Met Office Hadley Centre, Exeter, UK
  • 12CICERO Center for International Climate and Environmental Research, Oslo, Norway
  • 13Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland
  • 14Environment Canada, Montréal, Canada
  • 15Research Institute for Applied Mechanics, Kyushu University, 6-1 Kasuga-koen, Kasuga, Fukuoka, Japan
  • 16National Center for Atmospheric Research (NCAR), Boulder, Colorado, USA

Abstract. This study presents a multi-parameter analysis of aerosol trends over the last two decades at regional and global scales. Regional time series have been computed for a set of nine optical, chemical composition and mass aerosol properties by using the observations of several ground-based networks. From these regional time series the aerosol trends have been derived for different regions of the world. Most of the properties related to aerosol loading exhibit negative trends, both at the surface and in the total atmospheric column. Significant decreases of aerosol optical depth (AOD) are found in Europe, North America, South America and North Africa, ranging from −1.3 %/yr to −3.1 %/yr. An error and representativity analysis of the incomplete observational data has been performed using model data subsets in order to investigate how likely the observed trends represent the actual trends happening in the regions over the full study period from 2000 to 2014. This analysis reveals that significant uncertainty is associated with some of the regional trends due to time and space sampling deficiencies. The set of observed regional trends has then been used for the evaluation of the climate models and their skills in reproducing the aerosol trends. Model performance is found to vary depending on the parameters and the regions of the world. The models tend to capture trends in AOD, column Angstrom exponent, sulfate and particulate matter well (except in North Africa), but show larger discrepancies for coarse mode AOD. The rather good agreement of the trends, across different aerosol parameters between models and observations, when co-locating them in time and space, implies that global model trends, including those in poorly monitored regions, are likely correct. The models can help to provide a global picture of the aerosol trends by filling the gaps in regions not covered by observations. The calculation of aerosol trends at a global scale reveals a different picture from the one depicted by solely relying on ground based observations. Using a model with complete diagnostics (NorESM2) we find a global increase of AOD of about 0.2 %/yr between 2000 and 2014, primarily caused by an increase of the loads of organic aerosol, sulfate and black carbon.

Augustin Mortier et al.

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Short summary
We present a multi-parameter analysis of the aerosol trends over the last two decades in the different regions of the world. In most of the regions, ground based observations show a decrease of the aerosol content in both the total atmospheric column and at the surface. The use of climate models, which have been assessed against these observations, reveals an increase of the total aerosols load, which is not seen with the single use of observation due to partial coverage in space and time.
We present a multi-parameter analysis of the aerosol trends over the last two decades in the...
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