Journal cover Journal topic
The Cryosphere An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/tc-2018-91
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Brief communication
15 May 2018
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal The Cryosphere (TC).
Recent changes in summer Greenland blocking captured by none of the CMIP5 models
Edward Hanna1, Xavier Fettweis2, and Richard J. Hall1 1School of Geography and Lincoln Centre forWater and Planetary Health, University of Lincoln, UK
2Laboratory of Climatology, Department of Geography, University of Liège, Liège, Belgium
Abstract. Recent studies note a significant increase in high-pressure blocking over the Greenland region (Greenland Blocking Index, GBI) in summer since the 1990s. Such a general circulation change, indicated by a negative trend in the North Atlantic Oscillation (NAO) index, is generally highlighted as a major driver of recent surface melt records observed on the Greenland Ice Sheet (GrIS). Here we compare reanalysis-based GBI records with those from the Coupled Model Intercomparison Project 5 (CMIP5) suite of global climate models over 1950–2100. We find that the recent summer GBI increase lies well outside the range of modelled past reconstructions (Historical scenario) and future GBI projections (RCP4.5 and RCP8.5). The models consistently project a future decrease in GBI (linked to an increase in NAO), which highlights a likely key deficiency of current climate models if the recently-observed circulation changes continue to persist. Given well-established connections between atmospheric pressure over the Greenland region and air temperature and precipitation extremes downstream, e.g. over Northwest Europe, this brings into question the accuracy of simulated North Atlantic jet stream changes and resulting climatological anomalies over densely populated regions of northern Europe as well as of future projections of GrIS mass balance produced using global and regional climate models.
Citation: Hanna, E., Fettweis, X., and Hall, R. J.: Recent changes in summer Greenland blocking captured by none of the CMIP5 models, The Cryosphere Discuss., https://doi.org/10.5194/tc-2018-91, in review, 2018.
Edward Hanna et al.
Edward Hanna et al.
Edward Hanna et al.

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Short summary
The latest/recent generation of global climate models does not simulate the recent (last 30 years') increase in atmospheric high pressure over Greenland in summer but more rather projects decreasing pressure. This difference between climate models and observations raises serious questions about the ability of the models to accurately represent future changes in Greenland climate and ice-sheet mass balance. There are also likely effects on climate predictions downstream, e.g. over Europe.
The latest/recent generation of global climate models does not simulate the recent (last 30...
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