Climate Dynamics

, Volume 38, Issue 5–6, pp 877–896 | Cite as

Can oceanic reanalyses be used to assess recent anthropogenic changes and low-frequency internal variability of upper ocean temperature?

  • L. CorreEmail author
  • L. Terray
  • M. Balmaseda
  • A. Ribes
  • A. Weaver
Original Paper


A multivariate analysis of the upper ocean thermal structure is used to examine the recent long-term changes and decadal variability in the upper ocean heat content as represented by model-based ocean reanalyses and a model-independent objective analysis. The three variables used are the mean temperature above the 14°C isotherm, its depth and a fixed depth mean temperature (250 m mean temperature). The mean temperature above the 14°C isotherm is a convenient, albeit simple, way to isolate thermodynamical changes by filtering out dynamical changes related to thermocline vertical displacements. The global upper ocean observations and reanalyses exhibit very similar warming trends (0.045°C per decade) over the period 1965–2005, superimposed with marked decadal variability in the 1970s and 1980s. The spatial patterns of the regression between indices (representative of anthropogenic changes and known modes of internal decadal variability), and the three variables associated with the ocean heat content are used as fingerprint to separate out the different contributions. The choice of variables provides information about the local heat absorption, vertical distribution and horizontal redistribution of heat, this latter being suggestive of changes in ocean circulation. The discrepancy between the objective analysis and the reanalyses, as well as the spread among the different reanalyses, are used as a simple estimate of ocean state uncertainties. Two robust findings result from this analysis: (1) the signature of anthropogenic changes is qualitatively different from those of the internal decadal variability associated to the Pacific Interdecadal Oscillation and the Atlantic Meridional Oscillation, and (2) the anthropogenic changes in ocean heat content do not only consist of local heat absorption, but are likely related with changes in the ocean circulation, with a clear shallowing of the tropical thermocline in the Pacific and Indian oceans.


Anthropogenic climate change Internal variability Oceanic reanalyses Observations Upper ocean temperature 



The ENSEMBLES data used in this work was funded by the EU FP6 Integrated Project ENSEMBLES (contract number 505539) whose support is gratefully acknowledged. In particular, the authors thank Philippe Rogel for his assistance and advice with the reanalyses. The SODA data were obtained from the IRI/LDEO Climate Data Library Web site ( We are very grateful to Simon Good who provided the EN3_v2a version of the ENACT/ENSEMBLES quality-controlled dataset, and Matthew Palmer who provided the code we used to filter the data. We acknowledge the modeling groups, the Program for Climate Model Diagnosis and Intercomparison (PCMDI) and the WCRP’s Working Group on Coupled Modelling (WGCM) for their roles in making available the WCRP CMIP3 multi-model dataset. Support of this dataset is provided by the Office of Science, U.S. Department of Energy. We thank Gilles Reverdin, Thierry Delcroix, Sophie Cravatte and Gael Alory for stimulating discussions on this work, and anonymous reviewers whose comments helped to improve this manuscript. The figures were produced with the NCL software developed at NCAR.


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Copyright information

© Springer-Verlag 2010

Authors and Affiliations

  • L. Corre
    • 1
    Email author
  • L. Terray
    • 1
  • M. Balmaseda
    • 2
  • A. Ribes
    • 3
  • A. Weaver
    • 1
  1. 1.Cerfacs-CNRSToulouseFrance
  2. 2.E.C.M.W.FReadingUK
  3. 3.CNRM-GAME, Météo France-CNRSToulouseFrance

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