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Problems Modelling Antarctic Ice Sheet and Southern Ocean Temps

Paper Reviewed
Schneider, D.P. and Reusch, D.B. 2016. Antarctic and Southern Ocean Surface Temperatures in CMIP5 Models in the Context of the Surface Energy Budget. Journal of Climate 29: 1689-1716.

In their important study of 26 structurally-different CMIP5 climate models, Schneider and Reusch (2016) examine "the biases, inter-model spread, and inter-model range of surface air temperature (SAT) across the Antarctic ice sheet [AIS] and Southern Ocean." And what did they thereby learn?

The two U.S. researchers report that their work revealed that "[1] most models and [2] the ensemble mean are warm-biased over the Southern Ocean during late summer," as a result of (3,4) "excessive shortwave radiation in early summer and midsummer," that (5) "in winter, all models have a strong negative net longwave radiation bias over the AIS," that (6) "most models have a modest negative longwave radiation bias over the ocean," that (7,8) "in both domains, the deficit in net longwave radiation is mostly accounted for by a similar deficit in downward longwave radiation," which can be described by (9) "insufficient cloud radiative forcing."

In commenting on their findings, Schneider and Reusch write that the net longwave radiation bias over the AIS suggests that (10) "the lower atmosphere is too stable in CMIP5 models, similar to reported biases for the Arctic," as described by Pithan et al. (2014), while further noting that "cloud radiative forcing biases could reflect the fact that [11] "most global atmospheric models have not been optimized for the unique meteorological conditions of Antarctica." And so we all hope that this latter problem may soon be resolved.

Pithan, F., Medeiros, B. and Mauritsen, T. 2014. Mixed-phase clouds cause climate model biases in Arctic wintertime temperature inversions. Climate Dynamics 43: 289-303.

Posted 15 July 2016