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Exploring a Plethora of Biases in State-of-the-Art Climate Models

Paper Reviewed
Zhang, L., Wang, C., Song, Z. and Lee, S.-K. 2014. Remote effect of the model cold bias in the tropical North Atlantic on the warm bias in the tropical southeastern Pacific. Journal of Advances in Modeling Earth Systems 6: 1016-1026.

Introducing their study, Zhang et al. (2014) write that "most state-of-the-art climate models show significant systematic biases in the tropical south-eastern Pacific (SEP) and tropical North Atlantic (TNA)," which "manifest themselves as the sea surface temperature (SST) in the SEP being too warm and the SST in the TNA being too cold," with the result that "as the cold SST biases appear in the TNA, the warm SST biases also occur in the SEP," which indicates that "if climate models cannot succeed in simulating the TNA variability, they will also fail at least partially in the SEP."

In discussing the subject further, the four researchers report that "most climate models fail to reproduce the observed seasonal cycle in the eastern tropical Pacific," citing Szoeke and Xie (2008) and Mechoso et al. (1995), while further noting that "one of the most common errors in climate models is a warm SST bias in the SEP, with the warm bias extending thousands of kilometers off the coast of Peru."

Based on the output of 18 Coupled Model Intercomparison Project Phase 5 (CMIP5) GCM runs corresponding to the historical collection of simulations assembled by Taylor et al. (2012), Zhang et al. next go on to demonstrate that "model simulations in CMIP5 show a large cold SST bias in the TNA, with ensemble mean amplitude up to 2.5°C." And they add that "similar to the cold bias in the TNA, the SEP warm SST bias is significant in all models and occurs in all seasons."

Clearly, therefore, even the world's most advanced climate models still fall short of what is required to provide even a glimpse of what the future might possibly hold for these regions in terms of these local biases; and Zhang et al. thus bemoan the many real-world complexities of "regional feedbacks between stratocumulus clouds, surface winds, upwelling, coastal currents and SST in the SEP region," which they say "are poorly represented in many climate models."

Mechoso, C.R., 1995. The seasonal cycle over the tropical Pacific in coupled ocean-atmosphere general circulation models. Monthly Weather Review 123: 2825-2838.

Szoeke, S.P. and Xie, S.-P. 2008. The Tropical Eastern Pacific Seasonal Cycle: Assessment of Errors and Mechanisms in IPCC AR4 Coupled Ocean-Atmosphere General Circulation Models. Journal of Climate 21: 2573-2590.

Taylor, K.E., Stouffer, R.J. and Meehl, G.A. 2012. An overview of CMIP5 and the experiment design. Bulletin of the American Meteorological Society 93: 485-498.

Posted 1 June 2015