Articles | Volume 11, issue 21
Atmos. Chem. Phys., 11, 11175–11183, 2011
Atmos. Chem. Phys., 11, 11175–11183, 2011

Research article 10 Nov 2011

Research article | 10 Nov 2011

Rate of non-linearity in DMS aerosol-cloud-climate interactions

M. A. Thomas1,3, P. Suntharalingam1, L. Pozzoli2,*, A. Devasthale3, S. Kloster4,5, S. Rast5, J. Feichter5, and T. M. Lenton1,6 M. A. Thomas et al.
  • 1School of Environmental Sciences, University of East Anglia, Norwich, UK
  • 2European Commission, Joint Research Centre, Institute for Environment and Sustainability, Ispra, Italy
  • 3Swedish Meteorological and Hydrological Institute, Norrkoping, Sweden
  • 4Earth and Atmospheric Sciences, Cornell University, Ithaca, NY, USA
  • 5Department of Atmospheric Sciences, Max-Planck-Institute for Meteorology, Hamburg, Germany
  • 6Department of Geography, University of Exeter, Exeter, Devon, UK
  • *now at: Eurasia Institute of Earth Sciences, Istanbul Technical University, Istanbul, Turkey

Abstract. The degree of non-linearity in DMS-cloud-climate interactions is assessed using the ECHAM5-HAMMOZ model by taking into account end-to-end aerosol chemistry-cloud microphysics link. The evaluation is made over the Southern oceans in austral summer, a region of minimal anthropogenic influence. In this study, we compare the DMS-derived changes in the aerosol and cloud microphysical properties between a baseline simulation with the ocean DMS emissions from a prescribed climatology, and a scenario where the DMS emissions are doubled. Our results show that doubling the DMS emissions in the current climate results in a non-linear response in atmospheric DMS burden and subsequently, in SO2 and H2SO4 burdens due to inadequate OH oxidation. The aerosol optical depth increases by only ~20 % in the 30° S–75° S belt in the SH summer months. This increases the vertically integrated cloud droplet number concentrations (CDNC) by 25 %. Since the vertically integrated liquid water vapor is constant in our model simulations, an increase in CDNC leads to a reduction in cloud droplet radius of 3.4 % over the Southern oceans in summer. The equivalent increase in cloud liquid water path is 10.7 %. The above changes in cloud microphysical properties result in a change in global annual mean radiative forcing at the TOA of −1.4 W m−2. The results suggest that the DMS-cloud microphysics link is highly non-linear. This has implications for future studies investigating the DMS-cloud climate feedbacks in a warming world and for studies evaluating geoengineering options to counteract warming by modulating low level marine clouds.

Final-revised paper