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Warm Biases and Climate Change Amplification in CMIP5 Models

Paper Reviewed
Cheruy, F., Dufresne, J.L., Hourdin, F. and Ducharne, A. 2014. Role of clouds and land-atmosphere coupling in midlatitude continental summer warm biases and climate change amplification in CMIP5 simulations. Geophysical Research Letters 41: 6493-6500.

Introducing their illuminating study of CMIP5 models that appeared in Geophysical Research Letters, Cheruy et al. (2014) write that "most state-of-the-art climate models from the Coupled Model Intercomparison Project (CMIP) tend to over-predict the summer near-surface temperature at mid-latitudes," citing the work of Christensen and Boberg (2012) and Mueller and Seneviratne (2014), while also noting that "it is the case for Regional Climate Models as well," citing Boberg and Christensen (2012) and Vautard et al. (2013). And in light of these disturbing facts, they employed a new "multi-model approach in an attempt to identify statistically robust relationships between various temperature and surface energy budget indices," relying mostly on linear multi-model regressions, based on a multi-model ensemble from the CMIP Phase 5 (CMIP5) database of Taylor et al. (2012).

When all of what they purposed to do was completed, the four French researchers found that (1) "over land, most state-of-the-art climate models contributing to Coupled Model Intercomparison Project Phase 5 (CMIP5) share a strong summertime warm bias in mid-latitude areas," that (2) "the most biased models overestimate solar incoming radiation," because of (3) "cloud deficit" and the fact that they (4) "have difficulty to sustain evaporation," as well as the fact that they (5) "overestimate the present climate net shortwave radiation," which (6) "increases more than average in the future," plus the fact that (7) "they also show a higher-than-average reduction of evaporative fraction in areas with soil moisture-limited evaporation regimes."

Continuing to quote the authors, "the above deficiencies of the present climate simulations impact future climate projections," in that "the same feedback mechanisms identified for the warm-biased areas for the present climate are in play for future climate projections," which unfortunate state of affairs can artificially amplify predicted climate warming at regional scales.

Boberg, F. and Christensen, J.H. 2012. Overestimation of Mediterranean summer temperature projections due to model deficiencies. Nature Climate Change 2: 433-436.

Christensen, J. and Boberg, F. 2012. Temperature dependent climate projection deficiencies in CMIP5 models. Geophysical Research Letters 39: 10.1029/2012GL053650.

Mueller, B. and Seneviratne, S.I. 2014. Systematic land climate and evapotranspiration biases in CMIP5 simulations. Geophysical Research Letters 41: 128-134.

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.

Vautard, R., Gobiet, A., Jacob, D, Belda, M., Colette, A., Déqué, M., Fernández, J., García-Díez, M., Goergen, K., Güttler, I., Halenka, T., Karacostas, T., Katragkou, E., Keuler, K., Kotlarski, S., Mayer, S., van Meijgaard, E., Nikulin, G., Patar?i?, M., Scinocca, J., Sobolowski, S., Suklitsch, M., Teichmann, C., Warrach-Sagi, K., Wulfmeyer, V. and Yiou, P. 2013. The simulation of European heat waves from an ensemble of regional climate models within the EURO-CORDEX project. Climate Dynamics 41: 2555-2575.

Posted 18 March 2015