Monday, April 15, 2013

Settled science: New paper finds climate models have a 50% consensus on Arctic sea ice

A paper published today in Climate of Past finds a 50% consensus by climate models on the response of Arctic sea ice to changes in solar radiation during the mid-Holocene. According to the authors, "Approximately one half of the models simulate a decrease in winter sea-ice extent and one half simulates an increase." The paper adds to many others demonstrating that climate models are unable to model the known climate of the past, much less the future. 

Clim. Past, 9, 969-982, 2013

The sensitivity of the Arctic sea ice to orbitally induced insolation changes: a study of the mid-Holocene Paleoclimate Modelling Intercomparison Project 2 and 3 simulations

M. Berger1,2, J. Brandefelt1,2, and J. Nilsson2,3
1Linné Flow Centre, Dept. of Mechanics, Royal Institute of Technology, Stockholm, Sweden
2Bert Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden
3Dept. of Meteorology, Stockholm University, Stockholm, Sweden

 Abstract. In the present work the Arctic sea ice in the mid-Holocene and the pre-industrial climates are analysed and compared on the basis of climate-model results from the Paleoclimate Modelling Intercomparison Project phase 2 (PMIP2) and phase 3 (PMIP3). The PMIP3 models generally simulate smaller and thinner sea-ice extents than the PMIP2 models both for the pre-industrial and the mid-Holocene climate. Further, the PMIP2 and PMIP3 models all simulate a smaller and thinner Arctic summer sea-ice cover in the mid-Holocene than in the pre-industrial control climate. The PMIP3 models also simulate thinner winter sea ice than the PMIP2 models. The winter sea-ice extent response, i.e. the difference between the mid-Holocene and the pre-industrial climate, varies among both PMIP2 and PMIP3 models. Approximately one half of the models simulate a decrease in winter sea-ice extent and one half simulates an increase. The model-mean summer sea-ice extent is 11 % (21 %) smaller in the mid-Holocene than in the pre-industrial climate simulations in the PMIP2 (PMIP3). In accordance with the simple model of Thorndike (1992), the sea-ice thickness response to the insolation change from the pre-industrial to the mid-Holocene is stronger in models with thicker ice in the pre-industrial climate simulation. Further, the analyses show that climate models for which the Arctic sea-ice responses to increasing atmospheric CO2concentrations are similar may simulate rather different sea-ice responses to the change in solar forcing between the mid-Holocene and the pre-industrial. For two specific models, which are analysed in detail, this difference is found to be associated with differences in the simulated cloud fractions in the summer Arctic; in the model with a larger cloud fraction the effect of insolation change is muted. A sub-set of the mid-Holocene simulations in the PMIP ensemble exhibit open water off the north-eastern coast of Greenland in summer, which can provide a fetch for surface waves. This is in broad agreement with recent analyses of sea-ice proxies, indicating that beach-ridges formed on the north-eastern coast of Greenland during the early- to mid-Holocene.

 Final Revised Paper (PDF, 2561 KB)   Discussion Paper (CPD)   Special Issue

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