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How Greenhouse Warming May -- Or May Not -- Impact ENSO

Paper Reviewed
Cai, W., Santoso, A., Wang, G., Yeh, S.-W., An, S.-I., Cobb, K.M., Collins, M., Guilyardi, E., Jin, F.-F., Kug, J.-S., Lengaigne, M., McPhaden, M.J., Takahashi, K., Timmermann, A., Vecchi, G., Watanabe, M. and Wu, L. 2015. ENSO and greenhouse warming. Nature Climate Change 5: 849-859.

A new study published in Nature Climate Change -- which is authored by 17 scientists from 8 different countries -- suggests a number of ways by which climate-model-predicted global warming may negatively impact Earth's climate, focusing on ENSO. But the paper's authors also temper their conclusions by listing several different ways in which today's state-of-the-art climate models fail to provide what is needed to support the models' negative predictions, due to the models' many inabilities to correctly perform as needed.

Focusing on significant problems that still pervade climate model projections, therefore, Cai et al. (2015) report that (1) "the tropical SST trend over recent decades has featured suppressed warming in the east, contrary to the expected pattern from climate models," that (2,3) "the common cold tongue and the double-ITCZ bias in the mean state have persisted for decades," and that (4) "we still know little about how other important characteristics of ENSO will respond to greenhouse warming," specifically identifying in this regard (5) "interactions between ENSO and the annual cycle," (6,7) "termination and onset of El Nino events," (8) "coupling between westerly wind bursts (WWBs) and El Niño," and (9,10) ENSO precursors and amplifying or damping mechanisms."

In addition, the 17 scientists report that the "parameterization of sub-grid physics such as [11] atmospheric convection, [12] cloud formation and [13] their coupling to the resolved dynamics remains inaccurate," that (14,15) "the genesis and evolution of ENSO can be affected by processes occurring in the Indian and Atlantic oceans," but that (16,17) "associated processes are not well understood," that (18,19) "an additional uncertainty is whether teleconnection patterns and intensity are correctly represented at regional scales, given that [20] the regional impacts from ENSO extremes might not be resolved by present climate models."

In closing, therefore, Cai et al. warn that (21,22) these "biases and deficiencies may impede realistic simulation of ENSO extremes of the present-day and future climate."

Posted 15 December 2015