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AOGCMs and global albedo

PI: Henning Rodhe
Institution: Stockholm University
Additional Investigators: Johannes Karlsson
We would like to carry out a study of how the GCMs behave when it comes to the global albedo.

The global heat budget, and thereby the mean surface temperature, is strongly dependent on the magnitude of the albedo. A change of only 1 % unit in global albedo corresponds to a change in surface temperature of as much as 1 K. In view of the relatively small year-to-year variations of the global mean temperature - not only during the contemporary record but during most of the Holocene - , the albedo has to remain remarkably stable. Which processes contribute to this stability and how might that have changed over the industrial period?The extent and type of clouds play a crucial role in determining the albedo. The global ensemble of clouds, most especially marine low clouds, therefore also has to be "well behaved" and could be part of a negative feedback (stabilizing) feedback loop.
In order to address this issue we would like to analyze the GCM albedo output and specifically study:

- how the albedo varies over the year, from hemisphere to hemisphere, year to year and during the longer simulated periods

- how the different models differ in these respects

- the spatial scales of albedo variations

- if there are systematic differences between the models that can be related e.g. to their cloud parameterization schemes.

- how well or extensively the various models have been compared to the extant data on cloud type, cover and albedo.

- the degree to which the models explicitly or implicitly have cloud albedo imbedded in a feedback loop.
  • Bender, F. A-M., H. Rodhe, R. J. Charlson, A. M.L. Ekman and N. Loeb, 2006: 22 views of the global albedo - comparison between 20 GCMs and two satellites. Tellus A, DOI: 10.1111/j.1600-0870.2006.00181.x. Accepted. Abstract. Edit.
  • Karlsson, J., and Svensson, G., and Rodhe, H., Cloud radiative forcing of subtropical low level clouds in global models. Climate Dynamics, doi:10.1007/s00382-007-0322-1. Accepted. Abstract. Full Article. Edit.

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