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Modelling the Asian Summer Monsoon: Another Revealing Analysis
Volume 17, Number 5: 29 January 2014

In the same issue of the same journal from which last week's editorial was drawn, Sperber et al. (2013) wrote that "nearly half of the world's population is dependent on monsoon rainfall for food and energy security," and that "the vagaries of its timing, duration and intensity are of major concern, especially over semi-arid regions where agriculture is the primary source of food." And, therefore, they evaluated how well the boreal summer Asian monsoon is represented by 25 Coupled Model Intercomparison Project-5 (CMIP5) and 22 CMIP3 climate models. And what did they find as a result of this exercise?

The eight researchers report that (1) "the onset of the monsoon over India is typically too late in the models," that (2) "the extension of the monsoon over eastern China, Korea, and Japan is under-estimated," while (3) "it is over-estimated over the subtropical western/central Pacific Ocean." They also note that (4) "the anti-correlation between anomalies of all-India rainfall and Niņo3.4 sea surface temperature is overly strong in CMIP3 and (5) typically too weak in CMIP5," that (6) "for both the ENSO-monsoon teleconnection and the East Asian zonal wind-rainfall teleconnection, the MMM [multi-model mean] inter-annual rainfall anomalies are weak compared to observations," and that (7) "simulation of intra-seasonal variability remains problematic."

In commenting on their several findings, Sperber et al. say that "the most important take away message is that in terms of the MMM, the CMIP5 models outperform the CMIP3 models for all of the diagnostics," which does indeed represent some degree of progress. But "even so," as they continue, they say "there are systematic errors that are consistent between the two vintages of models." And these common errors, which are enumerated above, constitute what one could well call the seven deadly sins of the CMIP3 and CMIP5 climate models.

Thus, and in a way forgiving the scientists who developed the 47 CMIP models with which they worked, and which continue to commit the seven deadly sins, they state that "given the multitude of physical processes and interactions that influence the monsoon, it is no wonder that simulation and prediction of the monsoon remain grand challenge problems," which one can only hope will someday be solved by some grand challenge scientists.

Sherwood, Keith and Craig Idso

Sperber, K.R., Annamalai, H., Kang, I.-S., Kitoh, A., Moise, A., Turner, A., Wang, B. and Zhou, T. 2013. The Asian summer monsoon: an intercomparison of CMIP5 vs. CMIP3 simulations of the late 20th century. Climate Dynamics 41: 2711-2744.