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Friday, March 30, 2012

Daniel J. Rowlands et al., Nature Geosci., 5 (2012); Broad range of 2050 warming from an observationally constrained large climate model ensemble

Nature Geoscience5256–260 (2012) doi:10.1038/ngeo1430

Broad range of 2050 warming from an observationally constrained large climate model ensemble


Incomplete understanding of three aspects of the climate system—equilibrium climate sensitivity, rate of ocean heat uptake and historical aerosol forcing—and the physical processes underlying them lead to uncertainties in our assessment of the global-mean temperature evolution in the twenty-first century12. Explorations of these uncertainties have so far relied on scaling approaches34, large ensembles of simplified climate models12, or small ensembles of complex coupled atmosphere–ocean general circulation models56 which under-represent uncertainties in key climate system properties derived from independent sources789. Here we present results from a multi-thousand-member perturbed-physics ensemble of transient coupled atmosphere–ocean general circulation model simulations. We find that model versions that reproduce observed surface temperature changes over the past 50 years show global-mean temperature increases of 1.4–3K by 2050, relative to 1961–1990, under a mid-range forcing scenario. This range of warming is broadly consistent with the expert assessment provided by the Intergovernmental Panel on Climate Change Fourth Assessment Report10, but extends towards larger warming than observed in ensembles-of-opportunity5 typically used for climate impact assessments. From our simulations, we conclude that warming by the middle of the twenty-first century that is stronger than earlier estimates is consistent with recent observed temperature changes and a mid-range ‘no mitigation’ scenario for greenhouse-gas emissions.

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