Abstract
Instrumental records, proxy data and climate modelling show that multidecadal variability is a dominant feature of North Atlantic sea-surface temperature variations1,2,3,4, with potential impacts on regional climate5. To understand the observed variability and to gauge any potential for climate predictions it is essential to identify the physical mechanisms that lead to this variability, and to explore the spatial and temporal characteristics of multidecadal variability modes. Here we use a coupled ocean–atmosphere general circulation model to show that the phasing of the multidecadal fluctuations in the North Atlantic during the past 600 years is, to a large degree, governed by changes in the external solar and volcanic forcings. We find that volcanoes play a particularly important part in the phasing of the multidecadal variability through their direct influence on tropical sea-surface temperatures, on the leading mode of northern-hemisphere atmosphere circulation and on the Atlantic thermohaline circulation. We suggest that the implications of our findings for decadal climate prediction are twofold: because volcanic eruptions cannot be predicted a decade in advance, longer-term climate predictability may prove challenging, whereas the systematic post-eruption changes in ocean and atmosphere may hold promise for shorter-term climate prediction.
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Acknowledgements
We thank M. Miles, T. Eldevik and T. Furevik for comments on an earlier version of the manuscript. This study has been supported by the Research Council of Norway through the NorClim and ARCWARM projects, and by the Program of Supercomputing. Financial support by the EU FP6 Integrated Project ENSEMBLES (Contract 505539) is acknowledged. This study also contributes to the EU FP6 integrated project THOR, and the DecCen project financed by the Research Council of Norway. This is Publication A296 from the Bjerknes Centre for Climate Research.
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O.H.O. conceived the study, designed the model experiments and wrote the initial manuscript. O.H.O., M.B. and L.S. carried out the BCM experiments. O.H.O. processed the model results and did the main analyses. H.D. contributed to the scientific results through discussions and analyses. All authors participated in writing the paper and analysing the results.
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Otterå, O., Bentsen, M., Drange, H. et al. External forcing as a metronome for Atlantic multidecadal variability. Nature Geosci 3, 688–694 (2010). https://doi.org/10.1038/ngeo955
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DOI: https://doi.org/10.1038/ngeo955
