Article

Observed fingerprint of a weakening Atlantic Ocean overturning circulation

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Abstract

The Atlantic meridional overturning circulation (AMOC)—a system of ocean currents in the North Atlantic—has a major impact on climate, yet its evolution during the industrial era is poorly known owing to a lack of direct current measurements. Here we provide evidence for a weakening of the AMOC by about 3 ± 1 sverdrups (around 15 per cent) since the mid-twentieth century. This weakening is revealed by a characteristic spatial and seasonal sea-surface temperature ‘fingerprint’—consisting of a pattern of cooling in the subpolar Atlantic Ocean and warming in the Gulf Stream region—and is calibrated through an ensemble of model simulations from the CMIP5 project. We find this fingerprint both in a high-resolution climate model in response to increasing atmospheric carbon dioxide concentrations, and in the temperature trends observed since the late nineteenth century. The pattern can be explained by a slowdown in the AMOC and reduced northward heat transport, as well as an associated northward shift of the Gulf Stream. Comparisons with recent direct measurements from the RAPID project and several other studies provide a consistent depiction of record-low AMOC values in recent years.

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References

  1. 1.

    Lenton, T. M. et al. Tipping elements in the Earth’s climate system. Proc. Natl Acad. Sci. USA 105, 1786–1793 (2008).

  2. 2.

    Rahmstorf, S. Ocean circulation and climate during the past 120,000 years. Nature 419, 207–214 (2002).

  3. 3.

    Masson-Delmotte, V. et al. in Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change Ch. 5 (eds Stocker, T. F. et al.) 383–464 (Cambridge Univ. Press, Cambridge, 2013).

  4. 4.

    Smeed, D. A. et al. Observed decline of the Atlantic meridional overturning circulation 2004–2012. Ocean Sci. 10, 29–38 (2014).

  5. 5.

    Dima, M. & Lohmann, G. Evidence for two distinct modes of large-scale ocean circulation changes over the last century. J. Clim. 23, 5–16 (2010).

  6. 6.

    Drijfhout, S., van Oldenborgh, G. J. & Cimatoribus, A. Is a decline of AMOC causing the warming hole above the North Atlantic in observed and modeled warming patterns? J. Clim. 25, 8373–8379 (2012).

  7. 7.

    Rahmstorf, S. et al. Exceptional twentieth-century slowdown in Atlantic Ocean overturning circulation. Nat. Clim. Chang. 5, 475–480 (2015); corrigendum 5, 956 (2015).

  8. 8.

    Booth, B. B. B., Dunstone, N. J., Halloran, P. R., Andrews, T. & Bellouin, N. Aerosols implicated as a prime driver of twentieth-century North Atlantic climate variability. Nature 484, 228–232 (2012). erratum 485, 534 (2012).

  9. 9.

    Saba, V. S. et al. Enhanced warming of the Northwest Atlantic Ocean under climate change. J. Geophys. Res. Oceans 121, 118–132 (2016).

  10. 10.

    Small, R. J. et al. A new synoptic scale resolving global climate simulation using the Community Earth System Model. J. Adv. Model. Earth Syst. 6, 1065–1094 (2014).

  11. 11.

    Delworth, T. L. et al. Simulated climate and climate change in the GFDL CM2.5 high-resolution coupled climate model. J. Clim. 25, 2755–2781 (2012).

  12. 12.

    Olson, R., An, S. I., Fan, Y., Evans, J. P. & Caesar, L. North Atlantic observations sharpen meridional overturning projections. Clim. Dyn. https://doi.org/10.1007/s00382-017-3867-7 (2017).

  13. 13.

    Zhang, R. Coherent surface-subsurface fingerprint of the Atlantic meridional overturning circulation. Geophys. Res. Lett. 35, L20705 (2008).

  14. 14.

    Zhang, R. & Vallis, G. K. The role of bottom vortex stretching on the path of the North Atlantic western boundary current and on the Northern Recirculation Gyre. J. Phys. Oceanogr. 37, 2053–2080 (2007).

  15. 15.

    Zhang, R. et al. Have aerosols caused the observed Atlantic multidecadal variability? J. Atmos. Sci. 70, 1135–1144 (2013).

  16. 16.

    Rayner, N. A. et al. Global analyses of sea surface temperature, sea ice, and night marine air temperature since the late nineteenth century. J. Geophys. Res. 108, D14 (2003).

  17. 17.

    Stocker, T. F. The seesaw effect. Science 282, 61–62 (1998).

  18. 18.

    Feulner, G., Rahmstorf, S., Levermann, A. & Volkwardt, S. On the origin of the surface air temperature difference between the hemispheres in Earth’s present-day climate. J. Clim. 26, 7136–7150 (2013).

  19. 19.

    Defrance, D. et al. Consequences of rapid ice sheet melting on the Sahelian population vulnerability. Proc. Natl Acad. Sci. USA 114, 6533–6538 (2017).

  20. 20.

    Taylor, K. E., Stouffer, R. J. & Meehl, G. A. An overview of CMIP5 and the experiment design. Bull. Am. Meteorol. Soc. 93, 485–498 (2012).

  21. 21.

    Robson, J., Hodson, D., Hawkins, E. & Sutton, R. Atlantic overturning in decline? Nat. Geosci. 7, 2–3 (2014).

  22. 22.

    Jackson, L. C., Peterson, K. A., Roberts, C. D. & Wood, R. A. Recent slowing of Atlantic overturning circulation as a recovery from earlier strengthening. Nat. Geosci. 9, 518–522 (2016).

  23. 23.

    Frajka-Williams, E. Estimating the Atlantic overturning at 26°N using satellite altimetry and cable measurements. Geophys. Res. Lett. 42, 3458–3464 (2015).

  24. 24.

    Kanzow, T. et al. Seasonal variability of the Atlantic Meridional Overturning Circulation at 26.5°N. J. Clim. 23, 5678–5698 (2010).

  25. 25.

    Latif, M. et al. Is the thermohaline circulation changing? J. Clim. 19, 4631–4637 (2006).

  26. 26.

    Frajka-Williams, E., Beaulieu, C. & Duchez, A. Emerging negative Atlantic multidecadal oscillation index in spite of warm subtropics. Sci. Rep. 7, 11224 (2017).

  27. 27.

    Cleveland, W. S. Robust locally weighted regression and smoothing scatterplots. J. Am. Stat. Assoc. 74, 829–836 (1979).

  28. 28.

    Sherwood, O. A., Lehmann, M. F., Schubert, C. J., Scott, D. B. & McCarthy, M. D. Nutrient regime shift in the western North Atlantic indicated by compound-specific delta15N of deep-sea gorgonian corals. Proc. Natl Acad. Sci. USA 108, 1011–1015 (2011).

  29. 29.

    Bakker, P., Clark, P. U., Golledge, N. R., Schmittner, A. & Weber, M. E. Centennial-scale Holocene climate variations amplified by Antarctic Ice Sheet discharge. Nature 541, 72–76 (2017).

  30. 30.

    Laepple, T. & Huybers, P. Ocean surface temperature variability: large model–data differences at decadal and longer periods. Proc. Natl Acad. Sci. USA 111, 16682–16687 (2014).

  31. 31.

    Duchez, A. et al. Drivers of exceptionally cold North Atlantic Ocean temperatures and their link to the 2015 European heat wave. Environ. Res. Lett. 11, 074004 (2016).

  32. 32.

    Haarsma, R. J., Selten, F. M. & Drijfhout, S. S. Decelerating Atlantic meridional overturning circulation main cause of future west European summer atmospheric circulation changes. Environ. Res. Lett. 10, 094007 (2015).

  33. 33.

    Jackson, L. C. et al. Global and European climate impacts of a slowdown of the AMOC in a high resolution GCM. Clim. Dyn. 45, 3299–3316 (2015).

  34. 34.

    Sallenger, A. H., Doran, K. S. & Howd, P. A. Hotspot of accelerated sea-level rise on the Atlantic coast of North America. Nat. Clim. Change 2, 884–888 (2012).

  35. 35.

    Ezer, T. Detecting changes in the transport of the Gulf Stream and the Atlantic overturning circulation from coastal sea level data: the extreme decline in 2009–2010 and estimated variations for 1935–2012. Global Planet. Change 129, 23–36 (2015).

  36. 36.

    Bakker, P. et al. Fate of the Atlantic Meridional Overturning Circulation: strong decline under continued warming and Greenland melting. Geophys. Res. Lett. 43, 12252–12260 (2016).

  37. 37.

    Böning, C. W., Behrens, E., Biastoch, A., Getzlaff, K. & Bamber, J. L. Emerging impact of Greenland meltwater on deepwater formation in the North Atlantic Ocean. Nat. Geosci. 9, 523–527 (2016).

  38. 38.

    Liu, W., Liu, Z. & Brady, E. C. Why is the AMOC monostable in coupled general circulation models? J. Clim. 27, 2427–2443 (2014).

  39. 39.

    Liu, W., Xie, S.-P., Liu, Z. & Zhu, J. Overlooked possibility of a collapsed Atlantic Meridional Overturning Circulation in warming climate. Sci. Adv. 3, e1601666 (2017).

  40. 40.

    Hofmann, M. & Rahmstorf, S. On the stability of the Atlantic meridional overturning circulation. Proc. Natl Acad. Sci. USA 106, 20584–20589 (2009).

  41. 41.

    Buckley, M. W. & Marshall, J. Observations, inferences, and mechanisms of the Atlantic Meridional Overturning Circulation: a review. Rev. Geophys. 54, 5–63 (2016).

  42. 42.

    Griffies, S. M. et al. Impacts on ocean heat from transient mesoscale eddies in a hierarchy of climate models. J. Clim. 28, 952–977 (2015).

  43. 43.

    Zhang, R. & Vallis, G. K. Impact of great salinity anomalies on the low-frequency variability of the North Atlantic climate. J. Clim. 19, 470–482 (2006).

  44. 44.

    Sanchez-Franks, A. & Zhang, R. Impact of the Atlantic meridional overturning circulation on the decadal variability of the Gulf Stream path and regional chlorophyll and nutrient concentrations. Geophys. Res. Lett. 42, 9889–9897 (2015).

  45. 45.

    Heuzé, C. North Atlantic deep water formation and AMOC in CMIP5 models. Ocean Sci. 13, 609–622 (2017).

  46. 46.

    Visbeck, M. H., Hurrell, J. W., Polvani, L. & Cullen, H. M. The North Atlantic Oscillation: past, present, and future. Proc. Natl Acad. Sci. USA 98, 12876–12877 (2001).

  47. 47.

    Frankignoul, C., Gastineau, G. & Kwon, Y.-O. Estimation of the SST response to anthropogenic and external forcing and its impact on the Atlantic Multidecadal Oscillation and the Pacific Decadal Oscillation. J. Clim. 30, 9871–9895 (2017).

  48. 48.

    Zhang, R., Delworth, T. L. & Held, I. M. Can the Atlantic Ocean drive the observed multidecadal variability in Northern Hemisphere mean temperature? Geophys. Res. Lett. 34, L02709 (2007).

  49. 49.

    O’Reilly, C. H., Huber, M., Woollings, T. & Zanna, L. The signature of low-frequency oceanic forcing in the Atlantic Multidecadal Oscillation. Geophys. Res. Lett. 43, 2810–2818 (2016).

  50. 50.

    Gastineau, G. & Frankignoul, C. Influence of the North Atlantic SST variability on the atmospheric circulation during the twentieth century. J. Clim. 28, 1396–1416 (2015).

  51. 51.

    Delworth, T. L. & Zeng, F. The impact of the North Atlantic Oscillation on climate through its influence on the Atlantic Meridional Overturning Circulation. J. Clim. 29, 941–962 (2016).

  52. 52.

    Delworth, T. L. et al. The central role of ocean dynamics in connecting the North Atlantic Oscillation to the extratropical component of the Atlantic Multidecadal Oscillation. J. Clim. 30, 3789–3805 (2017).

  53. 53.

    Zhang, R. On the persistence and coherence of subpolar sea surface temperature and salinity anomalies associated with the Atlantic multidecadal variability. Geophys. Res. Lett. 44, 7865–7875 (2017).

  54. 54.

    Huang, B. et al. Extended reconstructed sea surface temperature, version 5 (ERSSTv5): upgrades, validations, and intercomparisons. J. Clim. 30, 8179–8205 (2017).

  55. 55.

    Huang, B. et al. Extended reconstructed sea surface temperature version 4 (ERSST.v4). Part I: upgrades and Intercomparisons. J. Clim. 28, 911–930 (2015).

  56. 56.

    Smith, T. M., Reynolds, R. W., Peterson, T. C. & Lawrimore, J. Improvements to NOAA’s historical merged land–ocean surface temperature analysis (1880–2006). J. Clim. 21, 2283–2296 (2008).

  57. 57.

    Kaplan, A., Cane, M. A., Kushnir, Y., Clement, A. C., Blumenthal, M. B. & Rajagopalan, R. Analyses of global sea surface temperature 1856–1991. J. Geophys. Res. Oceans 103, 18567–18589 (1998).

  58. 58.

    Carton, J. A. & Giese, B. S. A reanalysis of ocean climate using Simple Ocean Data Assimilation (SODA). Mon. Weath. Rev 136, 2999–3017 (2008).

  59. 59.

    Hirahara, S., Ishii, M. & Fukuda, Y. Centennial-scale sea surface temperature analysis and its uncertainty. J. Clim. 27, 57–75 (2014).

  60. 60.

    Trenberth, K. E. & Shea, D. J. Atlantic hurricanes and natural variability in 2005. Geophys. Res. Lett. 33, L12704 (2006).

  61. 61.

    Hurrell, J. W. Decadal trends in the North Atlantic Oscillation: regional temperatures and precipitation. Science 269, 676–679 (1995).

  62. 62.

    Intergovermental Panel on Climate Change. Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (Cambridge University Press, Cambridge, 2013).

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Acknowledgements

We acknowledge the World Climate Research Programme’s Working Group on Coupled Modelling, which is responsible for CMIP, and we thank the climate modelling groups listed in Extended Data Table 1 for producing and making available their model output. For CMIP, the US Department of Energy’s Program for Climate Model Diagnosis and Intercomparison provides coordinating support and led the development of software infrastructure in partnership with the Global Organization for Earth System Science Portals. Data from the RAPID-WATCH meridional overturning circulation monitoring project were generated with funding from the Natural Environment Research Council and are freely available from www.rapid.ac.uk/rapidmoc. We thank L. Jackson for the GloSea5 reanalysis data, and E. Frajka-Williams for the AMOC reconstruction from satellite altimetry and cable measurements. We also thank the personel of National Oceanic and Atmospheric Administration's GFDL for investeing time and resources into the development of CM2.6, which was evaluated in this research. A.R. was funded by the Marie Curie Horizon2020 project CONCLIMA (grant number 703251). PIK is a Member of the Leibniz Association.

Reviewer information

Nature thanks S. Gulev, A. Schmittner and the other anonymous reviewer(s) for their contribution to the peer review of this work.

Author information

Affiliations

  1. Potsdam Institute for Climate Impact Research (PIK), Potsdam, Germany

    • L. Caesar
    • , S. Rahmstorf
    • , A. Robinson
    •  & G. Feulner
  2. Institute of Physics and Astronomy, University of Potsdam, Potsdam, Germany

    • L. Caesar
    •  & S. Rahmstorf
  3. Complutense University of Madrid, Madrid, Spain

    • A. Robinson
  4. Instituto de Geociencias, CSIC-UCM, Madrid, Spain

    • A. Robinson
  5. National and Kapodistrian University of Athens, Athens, Greece

    • A. Robinson
  6. National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Northeast Fisheries Science Center, Geophysical Fluid Dynamics Laboratory, Princeton University, Princeton, NJ, USA

    • V. Saba

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Contributions

L.C. performed the research and wrote the manuscript together with S.R. S.R. designed the study. A.R. performed the CMIP5 analyses. G.F. helped to interpret the results. V.S. provided the CM2.6 analysis and simulations. All authors discussed the results and provided input to the manuscript.

Competing interests

The authors declare no competing interests.

Corresponding authors

Correspondence to L. Caesar or S. Rahmstorf.

Extended data figures and tables

  1. Extended Data Fig. 1 Normalized SST trends in the HadISST data for different time periods.

    Observed linear SST trends (using annual HadISST data), calculated for different timespans to test the robustness of the linear SST trend pattern to the starting and ending years of the timespan. The pattern is normalized with the respective global mean SST trend. Regions that show below-average warming or cooling are in blue; regions that show above-average warming are in red.

  2. Extended Data Fig. 2 Comparison of global normalized SST trends.

    Linear SST trends during a CO2-doubling experiment using the GFDL CM2.6 climate model (top), and observed trends during 1870–2016 (HadISST data, bottom), both normalized with the respective global mean SST trends and using data from the November–May season. Regions that show cooling or below-average warming are in blue; regions that show above-average warming are in red. Note again that owing to the much greater climate change in the CO2-doubling experiment, the signal-to-noise ratio for the modelled SST trends is better than that for the observations, and thus the noise level is suppressed by the normalization.

  3. Extended Data Fig. 3 Histograms showing the distribution of the normalized longer-term trends.

    a, The distribution (grey bars) of all local trends, normalized to the global trends, from the HadISST data for 1870–2016, for latitudes between 60° S and 75° N. The distribution is located around µ = 1 with a standard deviation of σ = 0.66 (grey bars). The 5th and 95th percentiles are marked in darker grey. The distribution of the 1870–2016 trends for grid cells assigned to the subpolar gyre regions is shifted to lower or even negative values, with a median of x ̃ sg  = −0.17 (blue). The distribution of trends for grid cells in the Gulf Stream region are shifted to higher values, with a median of x ̃ gs  = 2.4 (red). The distributions are normalized to account for the different sample sizes of global, subpolar gyre and Gulf Stream regions. b, As for panel a, but for the CO2-doubling run of the CM2.6 model, with µ = 1.1, σ = 0.48, x ̃ sg  = −0.02 and x ̃ gs  = 2.4. The standard deviations of the model data are expected to be smaller than those of the observations because of the larger climate-change signal by which the model data are normalized; this reduces the ‘noise’ of short-term variability relative to the climate signal.

  4. Extended Data Fig. 4 Influence of the AMOC on the separation point of the Gulf Stream.

    a, The evolution of the Gulf Stream (GS) separation point compared with the AMOC strength in the CM2.6 control and CO2-doubling runs, as indicated by the Gulf Stream index44. The graph shows a link between a weaker AMOC and a northward shift of the separation point. b, Time series of the southward transport of the deep ocean current (summed between depths of 1,000 m and 4,000 m) at 40° N in the region between the US coast and 65° W (see Methods), showing a weakening DWBC during the CO2-doubling experiment. The thin lines show annual values, the thick lines show the 20-year LOWESS-smoothed values.

  5. Extended Data Fig. 5 Linear SST trends from a CO2-doubling experiment using the GFDL CM2.6 climate model, and observed long-term trends from different SST data products, normalized with the respective global mean SST trends.

    The trend from 1870 to 2016 was calculated using those datasets that provide data until the present (HadISST16, ERSSTv554, ERSSTv455, ERSSTv3b56 and Kaplan57). Otherwise, it was calculated from 1870 to the end of the available time period (SODA58 and COBE59; see Extended Data Table 1). The SODA data are given for a depth of 5 m instead of the surface; thus, the long-term trend differs for regions with ice cover. For the SODA data, the normalization was adjusted with surface SST data instead of the data at a 5-m depth, to make this dataset comparable to the others. All datasets show a prominent cooling in the subpolar gyre region; the high-resolution data (HadISST, COBE and SODA) also show pronounced warming in the Gulf Stream region.

  6. Extended Data Fig. 6 Time series of the AMOC anomaly for two definitions of the AMOC index.

    We calculated the AMOC anomaly from two AMOC indices and two model-based conversion factors. In red is the AMOC anomaly as defined by Rahmstorf et al.7 (HadCRUT4 data), updated with the latest data to 2016. In blue is the AMOC anomaly as defined herein (HadISST data). Thick lines are smoothed by a 10-year LOWESS filter. This smoothing filter is lower than that used in Fig. 6, in order to compare and show the two indices with a higher time resolution.

  7. Extended Data Fig. 7 Sensitivity to the extension of the subpolar gyre region regarding sea-ice cover.

    a, Left panel, our original subpolar gyre region (blue outline) and the average November–May sea-ice cover from 1870 to 2016 (blue shading, from HadISST data). Right panel, a reduced subpolar gyre region (green outline) that is always ice-free, compared with the maximum sea-ice cover for the November–May season from 1870 to 2016. b, Comparison of the AMOC indices based on these two regions. The thin lines show annual values, the thick lines show the 20-year LOWESS-smoothed values.

  8. Extended Data Fig. 8 Comparison of interdecadal variability of the AMOC index and the AMO index.

    a, We calculated the AMO index from the HadISST dataset after Trenberth and Shea60. This index is defined as the weighted mean SST over the North Atlantic (0° N to 80° N), relative to the mean SST from the period 1901–1970, but with the global mean SST (averaged over the global oceans from 60° S to 60° N) removed. The thin lines show annual values, the thick lines indicate the 20-year LOWESS-smoothed values. We show our AMOC index for comparison. b, As for panel a, but here the AMO index is compared with the interdecadal variability of our AMOC index—that is, the detrended 20-year LOWESS-smoothed index. The comparison shows that the AMO index has similar interdecadal variability to the AMOC index but is lacking the climatic trend found in the latter.

  9. Extended Data Fig. 9 Comparison of AMOC and NAO.

    a, Comparison of our AMOC index with the interdecadal variability in the NAO index (after Hurrell61), calculated as the sea-level pressure at the Lisbon station minus the sea-level pressure at the Stykkisholmur/Reykjavik station for the months December to March (DJFM). The thin lines show annual values, the thick lines show the 20-year LOWESS-smoothed values. The linear trend over the whole time period is shown with dashed lines. b, Lagged cross-correlation between the AMOC index and the NAO index shows that peak negative correlation occurs when the AMOC leads the NAO by three years, with R = −0.54. The red lines mark the 95% significance level.

  10. Extended Data Table 1 Detailed data and model information

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