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
Received: 20 Jan 2011 – Published in Atmos. Chem. Phys. Discuss.: 18 May 2011
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.
Revised: 12 Sep 2011 – Accepted: 03 Nov 2011 – Published: 10 Nov 2011
Thomas, M. A., Suntharalingam, P., Pozzoli, L., Devasthale, A., Kloster, S., Rast, S., Feichter, J., and Lenton, T. M.: Rate of non-linearity in DMS aerosol-cloud-climate interactions, Atmos. Chem. Phys., 11, 11175-11183, doi:10.5194/acp-11-11175-2011, 2011.