Do sophisticated parameterizations of aerosol-cloud interactions in CMIP5 models improve the representation of recent observed temperature trends?

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Thursday, 6 February 2014: 2:45 PM
Room C207 (The Georgia World Congress Center )
Annica Ekman, Stockholm University, Stockholm, Sweden

Output from a subset of models from the CMIP5 archive was compared with the latitudinal distribution of observed surface temperature trends between the years 1965 and 2004. By comparing different model simulations, including and excluding the effects of changes in aerosol forcing, the influence of different representations of aerosols and aerosol indirect effects on modeled surface temperature trends was evaluated. When changes in aerosol concentrations over time were considered, the models that include more sophisticated parameterizations of aerosol activation into cloud droplets, i.e. models where the cloud droplet number concentration (CDNC) is a function of the modeled supersaturation as well as the aerosol concentration and composition, improved in a larger number of regions than the other models. The one model excluding all aerosol indirect effects improved in the least number of regions. No clear difference could be found between models that include an explicit aerosol module and the ones that utilize prescribed aerosol fields. A majority of the models agree on that the change in aerosol emissions between 1965 and 2004 has induced a negative mean global and tropical net surface radiative flux perturbation (RFP). However, at mid- and high-latitudes, 3 to 5 out of eleven models predict a positive surface RFP. The models that include no aerosol effects on the precipitation formation rate (cloud lifetime or Albrecht effect) all predict a positive surface RFP at mid- and high latitudes. The models that include more sophisticated parameterizations of aerosol activation into cloud droplets instead predict a negative surface RFP.