Climate Dynamics

, Volume 50, Issue 9–10, pp 3687–3698 | Cite as

Historical forcings as main drivers of the Atlantic multidecadal variability in the CESM large ensemble

  • Katinka BellomoEmail author
  • Lisa N. Murphy
  • Mark A. Cane
  • Amy C. Clement
  • Lorenzo M. Polvani


Previous studies suggest that internal variability, in particular the Atlantic Meridional Overturning Circulation (AMOC), drives the Atlantic Multidecadal Oscillation (AMV), while external radiative forcing only creates a steady increase in sea surface temperature (SST). This view has been recently challenged and new evidence has emerged that aerosols and greenhouse gases could play a role in driving the AMV. Here we examine the drivers of the AMV using the Community Earth System Model (CESM) Large Ensemble and Last Millennium Ensemble. By computing the ensemble mean we isolate the radiatively forced component of the AMV, while we estimate the role of internal variability using the ensemble spread. We find that phase changes of the AMV over the years 1854–2005 can be explained only in the presence of varying historical forcing. Further, we find that internal variability is large in North Atlantic SST at timescales shorter than 10–25 years, but at longer timescales the forced response dominates. Single forcing experiments show that greenhouse gases and tropospheric aerosols are the main drivers of the AMV in the latter part of the twentieth century. Finally, we show that the forced spatial pattern of SST is not distinct from the internal variability pattern, which has implications for detection and attribution.



KB was funded by a cooperative agreement between NASA and Columbia University (NNX15AJ05A). AC and LM were funded by NSF P2C2 program. Large ensemble data are made available by the CESM Large Ensemble Community Project and supercomputing resources provided by NSF/CISL/Yellowstone. NOAA ERSSTv4 data is provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA, from their web site at We thank two anonymous reviewers for helping improving the analysis presented here.


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Copyright information

© Springer-Verlag GmbH Germany 2017

Authors and Affiliations

  1. 1.Lamont-Doherty Earth Observatory of Columbia UniversityPalisadesUSA
  2. 2.Rosenstiel School of Marine and Atmospheric ScienceUniversity of MiamiMiamiUSA
  3. 3.Department of Applied Physics and Applied MathematicsColumbia UniversityNew YorkUSA

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