Articles | Volume 14, issue 22
Atmos. Chem. Phys., 14, 12465–12477, 2014
Atmos. Chem. Phys., 14, 12465–12477, 2014
Research article
27 Nov 2014
Research article | 27 Nov 2014

Modelled black carbon radiative forcing and atmospheric lifetime in AeroCom Phase II constrained by aircraft observations

B. H. Samset1, G. Myhre1, A. Herber2, Y. Kondo3, S.-M. Li4, N. Moteki3, M. Koike3, N. Oshima5, J. P. Schwarz6,19, Y. Balkanski7, S. E. Bauer8, N. Bellouin9,*, T. K. Berntsen1, H. Bian10, M. Chin11, T. Diehl11,20,**, R. C. Easter12, S. J. Ghan12, T. Iversen13,21,22, A. Kirkevåg13, J.-F. Lamarque14, G. Lin15, X. Liu16, J. E. Penner15, M. Schulz13, Ø. Seland13, R. B. Skeie1, P. Stier17, T. Takemura18, K. Tsigaridis8, and K. Zhang12 B. H. Samset et al.
  • 1Center for International Climate and Environmental Research – Oslo (CICERO), Oslo, Norway
  • 2Alfred Wegener Institute for Polar and Marine Research in the Helmholtz Association, Bürgermeister-Smidt-Straße 20, 27568 Bremerhaven, Germany
  • 3Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo, Tokyo, Japan
  • 4Air Quality Research Division, Science and Technology Branch, Environment Canada, 4905 Dufferin Street, Toronto, Ontario, M3H 5T4, Canada
  • 5Meteorological Research Institute, Tsukuba, Ibaraki Japan
  • 6Chemical Sciences Division, Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO, USA
  • 7Laboratoire des Sciences du Climat et de l'Environnement, CEA-CNRS-UVSQ, Gif-sur-Yvette, France
  • 8NASA Goddard Institute for Space Studies and Columbia Earth Institute, New York, NY, USA
  • 9Met Office Hadley Centre, Exeter, UK
  • 10Joint Center for Earth Systems Technology, University of Maryland Baltimore County, MD, USA
  • 11NASA Goddard Space Flight Center, Greenbelt, MD, USA
  • 12Pacific Northwest National Laboratory, Richland, WA, USA
  • 13Norwegian Meteorological Institute, Oslo, Norway
  • 14NCAR Earth System Laboratory, National Center for Atmospheric Research, Boulder, CO, USA
  • 15Department of Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, MI, USA
  • 16Department of Atmospheric Science, University of Wyoming, Laramie, WY, USA
  • 17Department of Physics, University of Oxford, Oxford, UK
  • 18Research Institute for Applied Mechanics, Kyushu University, Fukuoka, Japan
  • 19Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, CO, USA
  • 20Universities Space Research Association, Columbia, MD, USA
  • 21Department of Geosciences, University of Oslo, Oslo, Norway
  • 22ECMWF, Shinfield Park, RG2 9AX, Reading, UK
  • *Department of Meteorology, University of Reading, Reading, UK
  • **European Commission at the Joint Research Center, Ispra, Italy

Abstract. Atmospheric black carbon (BC) absorbs solar radiation, and exacerbates global warming through exerting positive radiative forcing (RF). However, the contribution of BC to ongoing changes in global climate is under debate. Anthropogenic BC emissions, and the resulting distribution of BC concentration, are highly uncertain. In particular, long-range transport and processes affecting BC atmospheric lifetime are poorly understood. Here we discuss whether recent assessments may have overestimated present-day BC radiative forcing in remote regions. We compare vertical profiles of BC concentration from four recent aircraft measurement campaigns to simulations by 13 aerosol models participating in the AeroCom Phase II intercomparison. An atmospheric lifetime of BC of less than 5 days is shown to be essential for reproducing observations in remote ocean regions, in line with other recent studies. Adjusting model results to measurements in remote regions, and at high altitudes, leads to a 25% reduction in AeroCom Phase II median direct BC forcing, from fossil fuel and biofuel burning, over the industrial era. The sensitivity of modelled forcing to BC vertical profile and lifetime highlights an urgent need for further flight campaigns, close to sources and in remote regions, to provide improved quantification of BC effects for use in climate policy.

Short summary
Far from black carbon (BC) emission sources, present climate models are unable to reproduce flight measurements. By comparing recent models with data, we find that the atmospheric lifetime of BC may be overestimated in models. By adjusting modeled BC concentrations to measurements in remote regions - over oceans and at high altitudes - we arrive at a reduced estimate for BC radiative forcing over the industrial era.
Final-revised paper