A Euro-Mediterranean tree-ring reconstruction of the winter NAO index since 910 C.E.
We develop a new reconstruction of the winter North Atlantic Oscillation (NAO) index using a network of 97 Euro-Mediterranean tree-ring series. The reconstruction covers the period 910–2018 C.E., making it the longest annually resolved estimate of winter NAO variability available. We use nested correlation-weighted principal components regression and the Maximum Entropy Bootstrap method to generate a 2400-member ensemble of reconstructions for estimating the final reconstruction and its quantile uncertainties. Extensive validation testing of the new reconstruction against data withheld from the calibration exercise demonstrates its skill. The skill level of the new reconstruction is also an improvement over two NAO reconstructions published earlier. Spectral analyses indicate that the new reconstruction behaves like a ‘white noise’ process with intermittent band-limited power, suggesting that the winter NAO is stochastically forced. The ‘white noise’ properties of our reconstruction are also shown to be consistent with the spectral properties of long instrumental NAO indices extending back to 1781 and NAO indices extracted from a large number of forced climate model runs covering the last millennium. In contrast, an annually resolved multi-proxy NAO reconstruction of comparable length, based in part on speleothem data, behaves more like externally forced ‘red noise’ process, which is inconsistent with our reconstruction, long observations, and forced model runs.
KeywordsNorth Atlantic Oscillation Euro-Mediterranean tree rings Millennium reconstruction Stochastic forcing
This research is supported by National Science Foundation Grant nos AGS-1501856, AGS-1734760, and AGS-1703029. We also acknowledge the World Climate Research Programme’s Working Group on Coupled Modelling, which is responsible for CMIP, and we thank the climate modeling groups for producing and making available their model output. The CMIP5 data used here was archived and served from the IRI/LDEO Climate Data Library. Lamont-Doherty Earth Observatory Contribution No. 8295.
- Cook ER, Seager R, Kushnir J, Briffa KR, Buentgen U, Frank D, Krusic PJ, Tegel W, van der Schrier G, Andreu-Hayles L, Baillie M, Baitttinger C, Bleicher N, Bonde N, Brown D, Carrer M, Cooper R, Cufar K, Dittmar C, Esper J, Griggs C, Gunnarson B, Gunther B, Gutierrez E, Haneca K, Helema S, Herzig F, Heussner K-U, Hofmann J, Janda J, Kontic R, Kose N, Kyncl T, Levanic T, Linderholm H, Manning S, Melvin T, Miles D, Neuwirth B, Nicolussi K, Nola P, Panayotov M, Popa I, Rothe A, Seftigen K, Seim A, Svarva H, Svoboda M, Thun T, Timonen M, Touchan R, Trotsiuk V, Trouet V, Walder F, Wazny T, Wilson R, Zang C (2015) Old world megadroughts and pluvials during the Common Era. Sci Adv 1(10):e1500561. https://doi.org/10.1126/sciadv.1500561 CrossRefGoogle Scholar
- Efroymson MA (1960) Multiple regression analysis. In: Ralston A, Wilf HS (eds) Mathematical methods for digital computers. Wiley, New YorkGoogle Scholar
- Hurrell JW, Kushnir Y, Visbeck M, Ottersen G (2003) An overview of the North Atlantic Oscillation. In Hurrell JW, Kushnir Y, Otterson G, Visbeck MH (eds) The North Atlantic Oscillation. AGU Geophysical Monograph, New York, vol 134, pp1–35Google Scholar
- Jones PD, Davies TD, Lister DH, Slonosky V, Jonsson T, Barring L, Jonsson P, Maheras P, Kolyva-Machera F, Barriendos M, Martin-Vide J, Rodrigue R, Alcoforado MJ, Wanner H, Pfister C, Luterbacher J, Rickli R, Schuepbach E, Kaas E, Schmith T, Jacobeit J, Beck C (1999) Monthly mean pressure reconstructions for Europe for the 1780–1995 period. Int J Clim 19:347–364CrossRefGoogle Scholar
- Jones PD, Osborn TJ, Briffa KR (2003) Pressure-based measures of the North Atlantic Oscillation (NAO): a comparison and an assessment of changes in the strength of the NAO and in its influence on surface climate parameters. In Hurrell JW, Kushnir Y, Otterson G, Visbeck MH (eds) The North Atlantic Oscillation. AGU Geophysical Monograph, New York, vol 134, pp 51–62Google Scholar
- Meko DM (1981) Applications of Box-Jenkins methods of time series analysis to the reconstruction of drought from tree rings. Dissertation, University of ArizonaGoogle Scholar
- Palmer JG, Cook E, Turney C, Allen K, Fenwick P, Cook B, O’Donnell A, Lough J, Grierson P, Baker P (2015) Drought variability in the eastern Australia and New Zealand summer drought atlas (ANZDA, CE 1500–2012) modulated by the Interdecadal Pacific Oscillation. Env Res Lett. https://doi.org/10.1088/1748-9326/10/12/124002 Google Scholar
- Schmidt GA, Jungclaus JH, Ammann CM, Bard E, Braconnot P, Crowley TJ, Delaygue G, Joos F, Krivova NA, Muscheler R, Otto-Bliesner BL, Pongratz J, Shindell DT, Solanki SK, Steinhilber F, Vieira LEA (2012) Climate forcing reconstructions for use in PMIP simulations of the Last Millennium (v1.1). Geosci Mod Dev 5:185–191. https://doi.org/10.5194/gmd-5-185-2012 CrossRefGoogle Scholar
- Stahle DW, Cook ER, Burnette DJ, Villanueva J, Cerano J, Burns JN, Griffin RD, Cook BI, Acuna R, Torbenson MCA, Sjezner P (2016) The Mexican drought atlas: tree-ring reconstructions of the soil moisture balance during the last pre-Hispanic, colonial, and modern eras. Quat Sci Rev 149:34–60CrossRefGoogle Scholar
- Stephenson DB, Wanner H, Bronnimann S, Luterbacheer J (2003) The history of scientific research on the North Atlantic Oscillation. In Hurrell JW, Kushnir Y, Otterson G, Visbeck MH (eds) The North Atlantic Oscillation. AGU Geophysical Monograph, New York, vol 134, pp 37–50Google Scholar
- Stockton CW, Glueck MF (1999) Long-term variability of the North Atlantic Oscillation (NAO). In: American Meteorological Society I0th Symposium on Global Change Studies, Dallas, Texas, pp 290–293Google Scholar
- Wassenburg JA, Immenhauser A, Richter DK, Niedermayr A, Riechelmann S, Fietzke J, Scholz D, Jochum KP, Fohlmeister J, Schroder-Ritzrau A, Sabaoui A, Riechelmann DFC, Schneider L, Esper J (2013) Moroccan speleothem and tree ring records suggest a variable positive state of the North Atlantic Oscillation during the Medieval Warm Period. Earth Planet Sci Lett 375:291–302CrossRefGoogle Scholar
- Wonnocott RJ, Wonnocott TH (1979) Econometrics, 2 ed. Wiley, HobokenGoogle Scholar