Research ArticleCLIMATOLOGY

Overlooked possibility of a collapsed Atlantic Meridional Overturning Circulation in warming climate

Science Advances  04 Jan 2017:
Vol. 3, no. 1, e1601666
DOI: 10.1126/sciadv.1601666
  • Fig. 1 AMOC stability in modern climate and AMOC response under global warming.

    (A) AMOC stability diagram where Embedded Image and Embedded Image are the AMOC stability indicators defined in Materials and Methods. The indicator values in modern climate are shown in solid circles for reanalysis data [Centro Euro-Mediterraneo sui Cambiamenti Climatici Global Ocean Physical Reanalysis System (C-GLORS; pink), Estimating the Circulation and Climate of the Ocean version 4 (ECCO-v4; brown), Ocean Reanalysis System 4 (ORAS4; green), and Simple Ocean Data Assimilation (SODA; yellow)], in gray triangles for the CMIP5 model simulations, and in blue and red diamonds for the CCSM3 CTL and ADJ runs. A positive or negative Embedded Image indicates that the AMOC resides in a stable or unstable regime. (B) Embedded Image, Embedded Image, and Embedded Image from reanalysis data, the CCSM3 CTL and ADJ runs with the same marker and color scheme as in (A), and the CMIP5 climate models in the form of the box-and-whisker plot. (C) Evolution of AMOC strength in the CTL (blue), CTLCO2 (light blue), ADJ (red), and ADJCO2 (orange), where the AMOC strength is defined as the maximum in the stream function below 500 m in the North Atlantic. A locally weighted scatterplot smoothing of 10-year intervals is applied to annual mean AMOC strength to remove interannual variability.

  • Fig. 2 Salinity and velocity profiles.

    Zonal mean (A) salinity and (B) baroclinic meridional velocity at the southern boundary (~34°S) of the Atlantic as a function of depth. psu, practical salinity units. Annual mean results are calculated from reanalysis data [C-GLORS (pink), ECCO-v4 (brown), ORAS4 (green), and SODA (yellow)], the CMIP5 model simulations (gray), and the CCSM3 CTL (blue) and ADJ (red) runs.

  • Fig. 3 Evolutions of freshwater transport and salinity.

    Decadal mean anomalies in double CO2 simulations (relative to the climatology in the CTL and ADJ) for freshwater transports Embedded Image (light green) and Embedded Image (pink) in (A) the CTLCO2 and (B) ADJCO2, for (C) Embedded Image in the CTLCO2 (light blue) and ADJCO2 (orange), and for (D) the Atlantic basin mean salinity ΔSAtl in the CTLCO2 (blue) and ADJCO2 (red). A 90-year running mean is applied to Embedded Image, Embedded Image, and Embedded Image during years 251 to 600, with results shown in thick lines. Smoothed Embedded Image (dark green) and Embedded Image (purple) are shown in (A) and (B), whereas smoothed Embedded Image is shown in (C), in blue for the CTLCO2 and in red for the ADJCO2.

  • Fig. 4 Long-term (after 300 years) responses of surface temperature and precipitation to CO2 increase.

    (A, C, and E ) Results of annual mean temperature (shading in °C): (A) the CTLCO2 minus the CTL (C) the ADJCO2 minus the ADJ, and (E) the difference between (C) and (A). (B, D, and F) Similar to (A), (C), and (E) but for the results of annual mean precipitation (shading in mm day−1).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/1/e1601666/DC1

    fig. S1. The depth and latitude diagram of annual mean AMOC stream function.

    fig. S2. Annual mean anomalies in double CO2 simulations.

    fig. S3. Short-term (0 to 30 years) surface temperature response to CO2 increase.

    fig. S4. Long-term (after 300 years) response of sea ice coverage to CO2 increase.

    fig. S5. Response of the Hadley cell 300 years after CO2 increase.

    fig. S6. Changes in the surface fluxes and variables over the North Atlantic in the first 30 years after CO2 increase.

    fig. S7. Annual mean SST and SSS biases.

    fig. S8. Observed and simulated formation areas of NADW and Atlantic multidecadal oscillation.

    table S1. The CMIP5 models used in this study and their sponsors, countries, and names.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. The depth and latitude diagram of annual mean AMOC stream function.
    • fig. S2. Annual mean anomalies in double CO2 simulations.
    • fig. S3. Short-term (0 to 30 years) surface temperature response to CO2 increase.
    • fig. S4. Long-term (after 300 years) response of sea ice coverage to CO2 increase.
    • fig. S5. Response of the Hadley cell 300 years after CO2 increase.
    • fig. S6. Changes in the surface fluxes and variables over the North Atlantic in the first 30 years after CO2 increase.
    • fig. S7. Annual mean SST and SSS biases.
    • fig. S8. Observed and simulated formation areas of NADW and Atlantic multidecadal oscillation.
    • table S1. The CMIP5 models used in this study and their sponsors, countries, and names.

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