New paper finds excuse #32 for the ‘pause’: ‘Explanations of the so-called ‘warming hiatus’ remain fragmented & implications…unclear’

New paper: “explanations of the so-called ‘warming hiatus’ remain fragmented & implications…unclear”

A new paper published in Nature finds excuse #32 for the 18 year “pause” in global warming that sophisticated IPCC climate models failed to predict. According to the paper, the IPCC models didn’t predict the pause because they are too complex, but if a model with “reduced complexity” and the already known changes of natural variability is used, all is well.

The simpler model uses observations of ENSO, solar activity, and stratospheric aerosols to retrospectively predict the known climate change, not nearly as challenging as making a true prospective prediction of climate change before the natural variability is known.

The authors state, “the explanations of the so-called ‘warming hiatus’ remain fragmented and the implications for long-term temperature projections are unclear,” but that their less complex model including a greater role for natural variability explains the “pause.”

Natural variability, radiative forcing and climate response in the recent hiatus reconciled

Markus Huber
& Reto Knutti

Corresponding author

Nature Geoscience (2014) doi:10.1038/ngeo2228

 06 March 2014 
 17 July 2014 
Published online
 17 August 2014

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Global mean surface warming over the past 15 years or so has been less than in earlier decades and than simulated by most climate models1. Natural variability2, 3, 4, a reduced radiative forcing5,6, 7, a smaller warming response to atmospheric carbon dioxide concentrations8, 9 and coverage bias in the observations10 have been identified as potential causes. However, the explanations of the so-called ‘warming hiatus’ remain fragmented and the implications for long-term temperature projections are unclear. Here we estimate the contribution of internal variability associated with the El Niño/Southern Oscillation (ENSO) using segments of unforced climate model control simulations that match the observed climate variability. We find that ENSO variability analogous to that between 1997 or 1998 and 2012 leads to a cooling trend of about −0.06 °C. In addition, updated solar and stratospheric aerosol forcings from observations explain a cooling trend of similar magnitude (−0.07 °C). Accounting for these adjusted trends we show that a climate model of reduced complexity with a transient climate response of about 1.8 °C is consistent with the temperature record of the past 15 years, as is the ensemble mean of the models in the Coupled Model Intercomparison Project Phase 5 (CMIP5). We conclude that there is little evidence for a systematic overestimation of the temperature response to increasing atmospheric CO2 concentrations in the CMIP5 ensemble.