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Simulating the Present-Day Arctic Atmosphere

Reference
de Boer, G., Chapman, W., Kay, J.E., Medeiros, B., Shupe, M.D., Vavrus, S. and Walsh, J. 2012. A characterization of the present-day Arctic atmosphere in CCSM4. Journal of Climate 25: 2676-2695.
Introducing their study, authors de Boer et al. (2012) write that "observed and projected changes in the Arctic region are some of the most striking concerns surrounding climate trends," noting that these trends "likely have important consequences both within the Arctic and globally." And they further note, in this regard, that "a new generation of Earth system models has been utilized to prepare climate projections for the fifth phase of the Coupled Model Intercomparison Project (CMIP5)," the results of which are planned to be used "in the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5)." Hence, it was only natural that they would want to determine how well these models actually do - or fail to do - what they are supposed to do. But the closest they could come to conducting such a test at this point in time was to interrogate the models used in the AR4 report of the IPCC. Thus, de Boer et al. simulated key features of the Arctic atmosphere in the Community Climate System Model, version 4 (CCSM4), and compared the results of those simulations "against observational and reanalysis datasets for the present-day (1981-2005)." And what were the results of that comparison?

Quoting the seven scientists with respect to problems they encountered in this endeavor, they report that: (1) "simulated surface air temperatures are found to be slightly too cold," (2) "evaluation of the sea level pressure [SLP] demonstrates some large biases, most noticeably an under simulation of the Beaufort High during spring and autumn," (3) "monthly Arctic-wide [SLP] biases of up to 13 mb are reported," (4) "cloud cover is under-predicted for all but summer months," (5) "cloud phase is demonstrated to be different from observations," (6) "simulated all-sky liquid water paths are too high," (7) "ice water path was generally too low," (8) "precipitation is found to be excessive over much of the Arctic compared to ERA-40 and the Global Precipitation Climatology Project estimates," as (9) "biases of 40% - 150% are calculated over northern North America, northern Greenland, and the Arctic Ocean," while (10) "over the Norwegian Sea ... evaporation is over-simulated by up to 3.5 mm/day," such that (11) "P-E is generally too high over much of the Arctic, particularly over coastal Greenland," (12) "CCSM4 over-predicts surface energy fluxes during summer months," and (13) "under-predicts it during winter," (14) "the strengths of surface inversions were found to be too great in CCSM4 when compared to ERA-40, with distributions showing a near-doubling of strength," and (15) "CCSM4 is found to have more inversions than ERA-40 for all months."

In what seems to be almost a tongue-in-cheek conclusion, de Boer et al. state that "CCSM4 provides a consistent representation of present-day Arctic climate," and they write that "in doing so it represents individual components of the Arctic atmosphere with respectable accuracy," which statement seems to us to be an egregious misuse of the word "respectable."

Archived 5 September 2012