Observational evidence for aerosols increasing upper tropospheric humidity
- 1Department of Physics, University of Helsinki, P.O. Box 48, 00014 Helsinki, Finland
- 2Met Office Hadley Centre, FitzRoy Road, Exeter, Devon, EX1 3PB, UK
- 3EUMETSAT, Eumetsat Allee 1, 64295 Darmstadt, Germany
- 4Tampere University of Technology, P.O. Box 692, 33101 Tampere, Finland
- 5Finnish Meteorological Institute, P.O. Box 503, 00101 Helsinki, Finland
- anow at: EMPA, Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, 8600 Dübendorf, Switzerland
Abstract. Aerosol–cloud interactions are the largest source of uncertainty in the radiative forcing of the global climate. A phenomenon not included in the estimates of the total net forcing is the potential increase in upper tropospheric humidity (UTH) by anthropogenic aerosols via changes in the microphysics of deep convection. Using remote sensing data over the ocean east of China in summer, we show that increased aerosol loads are associated with an UTH increase of 2.2 ± 1.5 in units of relative humidity. We show that humidification of aerosols or other meteorological covariation is very unlikely to be the cause of this result, indicating relevance for the global climate. In tropical moist air such an UTH increase leads to a regional radiative effect of 0.5 ± 0.4 W m−2. We conclude that the effect of aerosols on UTH should be included in future studies of anthropogenic climate change and climate sensitivity.