Anthropogenic aerosols may have increased upper tropospheric humidity in the 20th century Department of Physics, University of Helsinki, Helsinki, Finland
13 May 2011
Received: 20 August 2010 – Published in Atmos. Chem. Phys. Discuss.: 11 October 2010 Abstract. Recent simulations of deep convection with a spectral microphysics cloud
model show that an increase in aerosol concentration can have a significant
effect on the nature of convection with more ice precipitation and less warm
rain in polluted air. The cloud lifetime and the area covered by cloud
anvils of deep convection are also larger for polluted air. Therefore, it is
possible that the increase of anthropogenic aerosols in most of the 20th
century has increased humidity and perhaps also cloudiness in the mid- to
upper troposphere. Satellite data of upper tropospheric relative humidity in
1979–1997 and observed changes in cloudiness support this hypothesis. As
changes in upper tropospheric humidity strongly affect longwave radiation,
it is possible that anthropogenic aerosols have had a significant warming
effect in addition to their other known effects on radiation.
Revised: 13 April 2011 – Accepted: 14 April 2011 – Published: 13 May 2011
Citation: Bister, M. and Kulmala, M.: Anthropogenic aerosols may have increased upper tropospheric humidity in the 20th century, Atmos. Chem. Phys., 11, 4577-4586, doi:10.5194/acp-11-4577-2011, 2011.