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Climate Model Failures in the Southeast Pacific Ocean
Zheng, Y., Shinoda, T., Lin, J.-L. and Kiladis, G.N. 2011. Sea surface temperature biases under the stratus cloud deck in the Southeast Pacific Ocean in 19 IPCC AR4 coupled general circulation models. Journal of Climate 24: 4139-4164.

Climate in the Southeast Pacific (SEP) near the coast of Peru and Chile, in the words of the authors, "is controlled by complex upper-ocean, marine boundary layer and land processes and their interactions," and they say that variations in this system have "significant impacts on global climate," citing Ma et al. (1996), Miller (1977), Gordon et al. (2000) and Xie (2004). However, they write that "it is well known that coupled atmosphere-ocean general circulation models tend to have systematic errors in the SEP region, including a warm bias in sea surface temperature and too little cloud cover," as demonstrated by Mechoso et al. (1995), Ma et al. (1996), Gordon et al. (2000), McAvaney et al. (2001), Kiehl and Gent (2004), Large and Danabasoglu (2006), Wittenberg et al. (2006) and Lin (2007). And even though these biases have what they call "important impacts" on the simulation of earth's radiation budget and climate sensitivity, they say that "it is still uncertain" whether a similar bias is evident in most state-of-the-art coupled general circulation models [CGCMs] and to what extent the sea surface temperature [SST] biases are model dependent."

What was done
Hoping to lessen this uncertainty, and based on 20-year (1980-1999) model runs of the "Climate of the Twentieth Century" simulations of the nineteen CGCMs that figured prominently in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4), Zheng et al. examined systematic biases in SSTs under the stratus cloud deck in the SEP and upper-ocean processes relevant to those biases, attempting to isolate their causes. So what did they find?

What was learned
The four U.S. researchers learned that [1] "pronounced warm SST biases in a large portion of the southeast Pacific stratus region are found in all models," [2] "negative biases in net surface heat fluxes are evident in most of the models," [3] "biases in heat transport by Ekman currents largely contribute to warm SST biases both near the coast and the open ocean," [4] "in the coastal area, southwestward Ekman currents and upwelling in most models are much weaker than observed," [5] "in the open ocean, warm advection due to Ekman currents is overestimated," [6] "negative biases (cooling the ocean) in net surface heat flux are found in most CGCMs," [7] "positive biases in shortwave radiation are found in most models," because [8] most models "do not generate sufficient stratus clouds," and, last of all, [9] "most CGCMs underestimate alongshore winds and coastal upwelling."

What it means
With such yet-unresolved problems associated with nearly all of the CGCMs that were employed in the preparation of the IPCC's AR4 Report and that pertain to processes that are said to have important impacts on earth's climate sensitivity, it is no wonder that the projections of those models are greeted with a solid dose of skepticism by those who realize that it is the height of folly to use the output of such imperfect models as the reason for wanting to entirely restructure the way mankind acquires the energy that makes possible our current level of industrial and technological development.

Gordon, C.T., Rosati, A. and Gudgel, R. 2000. Tropical sensitivity of a coupled model to specified ISCCP low clouds. Journal of Climate 13: 2239-2260.

Kiehl, J.T. and Gent, P.R. 2004. The Community Climate system Model, version 2. Journal of Climate 17: 3666-3682.

Large, W.G. and Danabasoglu, G. 2006. Attribution and impacts of upper-ocean biases in CCSM3. Journal of Climate 19: 2325-2346.

Lin, J.-L. 2007. The double-ITCZ problem in IPCC AR4 coupled GCMs: Ocean-atmosphere feedback analysis. Journal of Climate 20: 4497-4525.

Ma, C.-C., Mechoso, C.R., Robertson, A.W. and Arakawa, A. 1996. Peruvian stratus clouds and the tropical Pacific circulation: A coupled ocean-atmosphere GCM study. Journal of Climate 9: 1635-1645.

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Mechoso, C.R., Robertson, A.W., Barth, N., Davey, M.K., Delecluse, P., Gent, P.R., Ineson, S., Kirtman, B., Latif, M., Le Treut, H., Nagai, T., Neelin, J.D., S.G.H., Polcher, J., Stockdale, T., Terray, L., Thual, O., and Tribbia, J.J. 1995. The seasonal cycle over the tropical Pacific in coupled ocean-atmosphere general circulation models. Monthly Weather Review 123: 2825-2838.

Miller, R.L. 1997. Tropical thermostats and low cloud cover. Journal of Climate 10: 409-440.

Wittenberg, A.T., Rosati, A., Lau, N.-C. and Ploshay, J.J. 2006. GFDL's CM2 global coupled climate models. Part III: Tropical Pacific climate and ENSO. Journal of Climate 19: 698-722.

Xie, S.-P. 2004. The shape of continents, air-sea interaction, and the rising branch of the Hadley circulation. In: Diaz, H.F. and Bradley, R.S. (Eds.). The Hadley Circulation: Past, Present and Future. Advances in Global Change Research 25: 121-152.

Reviewed 14 December 2011