Abstract
Most – or perhaps even all – of the observed variations in the winter North Atlantic Oscillation (NAO) index can be explained as internally-generated climate variability. The influence of external forcing factors on the observed NAO behaviour is still an open question. Two sea level pressure datasets yield different results for the strength of the winter NAO trend from the 1960s to the 1990s, though these trends from both datasets lie outside the 90% range of trends generated by the internal variability of climate models, and the latter is more precisely known now that over 8000 years of simulation under constant forcing is available for analysis. Similarly, a much expanded, multi-model ensemble of simulations under increasing anthropogenic forcing strengthens earlier findings of a shift in the mean state of the winter atmospheric circulation towards positive NAO conditions. There is considerable inter-model spread in both the magnitude of this response to increased forcing and in its regional structure, but of the 21 climate models analysed here, none showed an overall decrease in the mean level of the NAO index. If a shift towards positive NAO conditions is a realistic response to increasing anthropogenic forcing, then this signal has not yet emerged from the natural variability: observations since the 1990s show a return to lower values, and the 2009/2010 winter had the record negative NAO index in a record lasting almost two centuries. It is possible that anthropogenic forcing could be altering the temporal or spatial character of the interannual NAO variability, though only relatively small changes in pattern are evident when considering the multi-model ensemble as a whole and there is only weak evidence for an increase in the interannual variance.
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Allan RJ, Ansell TJ (2006) A new globally complete monthly historical mean sea level pressure data set (HadSLP2): 1850–2004. J Clim 19:5816–5842
Gillett NP, Graf HF, Osborn TJ (2003) Climate change and the North Atlantic Oscillation. In Hurrell JW, Kushnir Y, Ottersen G, Visbeck M (eds) North Atlantic Oscillation: climatic significance and environmental impact. Geophysical Monograph, vol 134. American Geophyscial Union, Washington, DC, pp 193–209
Hurrell JW, Deser C (2009) North Atlantic climate variability: the role of the North Atlantic Oscillation. J Mar Syst 78:28–41
Jones PD (1987) The early twentieth century Arctic high—fact or fiction? Clim Dyn 1:63–75. doi:10.1007/BF01054476
Jones PD, Jonsson T, Wheeler D (1997) Extension to the North Atlantic Oscillation using early instrumental pressure observations from Gibraltar and South-West Iceland. Int J Climatol 17:1433–1450
Jung T, Hilmer M, Ruprecht E, Kleppek S, Gulev SK, Zolina O (2003) Characteristics of the recent eastward shift of interannual NAO variability. J Clim 16:3371–3382
Kuzmina SI, Bengtsson L, Johannessen OM, Drange H, Bobylev LP, Miles MW (2005) The North Atlantic Oscillation and greenhouse-gas forcing. Geophys Res Lett 32:L04703. doi:10.1029/2004GL021064
López-Moreno JI, Vicente-Serrano SM (2008) Positive and negative phases of the wintertime North Atlantic Oscillation and drought occurrence over Europe: a multitemporal-scale approach. J Clim 21:1220–1243
Meehl GA, Covey C, Delworth T, Latif M, McAvaney B, Mitchell JFB, Stouffer RJ, Taylor KE (2007) The WCRP CMIP3 multi-model dataset: a new era in climate change research. Bull Am Meteorol Soc 88:1383–1394
Miller RL, Schmidt GA, Shindell DT (2006) Forced annular variations in the 20th century Intergovernmental Panel on Climate Change Fourth Assessment Report models. J Geophys Res 111:D18101. doi:10.1029/2005JD006323
Osborn TJ (2004) Simulating the winter North Atlantic Oscillation: the roles of internal variability and greenhouse gas forcing. Clim Dyn 22:605–623
Osborn TJ (2011) Winter 2009/2010 temperatures and a record-breaking North Atlantic Oscillation index. Weather 66:19–21
Osborn TJ, Briffa KR, Tett SFB, Jones PD, Trigo RM (1999) Evaluation of the North Atlantic Oscillation as simulated by a coupled climate model. Clim Dyn 15:685–702
Perlwitz J, Harnik N (2004) Downward coupling between the stratosphere and troposphere: the relative roles of wave and zonal mean processes. J Clim 17:4902–4909
Selten FM, Branstator GW, Dijkstra HA, Kliphuis M (2004) Tropical origins for recent and future Northern Hemisphere climate change. Geophys Res Lett 31:L21205. doi:10.1029/2004GL020739
Trenberth KE, Paolino DA (1980) The Northern Hemisphere sea level pressure data set, trends, errors and discontinuities. Mon Wea Rev 108:855–872
Trigo RM, Osborn TJ, Corte-Real J (2002) The North Atlantic Oscillation influence on Europe: climate impacts and associated physical mechanisms. Clim Res 20:9–17
Ulbrich U, Christoph M (1999) A shift of the NAO and increasing storm track activity over Europe due to anthropogenic greenhouse gas forcing. Clim Dyn 15:551–559
Acknowledgements
This work was supported by a Research Councils UK Academic Fellowship. The modelling groups, the Program for Climate Model Diagnosis and Intercomparison (PCMDI) and the WCRP’s Working Group on Coupled Modelling (WGCM) are acknowledged for their roles in making available the WCRP CMIP3 multi-model dataset. Support for CMIP3 dataset is provided by the Office of Science, U.S. Department of Energy.
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Osborn, T.J. (2011). Variability and Changes in the North Atlantic Oscillation Index. In: Vicente-Serrano, S., Trigo, R. (eds) Hydrological, Socioeconomic and Ecological Impacts of the North Atlantic Oscillation in the Mediterranean Region. Advances in Global Change Research, vol 46. Springer, Dordrecht. https://doi.org/10.1007/978-94-007-1372-7_2
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DOI: https://doi.org/10.1007/978-94-007-1372-7_2
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