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Observed Arctic sea-ice loss directly follows anthropogenic CO2 emission

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Science  11 Nov 2016:
Vol. 354, Issue 6313, pp. 747-750
DOI: 10.1126/science.aag2345
  • Fig. 1 Relationship between September Arctic sea-ice area and cumulative anthropogenic CO2 emissions.

    (A) Actual values. The thick blue line shows the 30-year running mean of observed September sea-ice area, and the thinner red lines the 30-year running means from CMIP5 model simulations. For reference, we also show the annual values of observed September sea-ice area, based from 1953 to 1978 on HadISST (31) (circles) and from 1979 to 2015 on the NSIDC sea-ice index (32) (diamonds; see methods for details). (B) Normalized simulations. For this plot, the simulated CMIP5 sea-ice area is normalized by dividing by the simulated sea-ice area at the onset of the transition period as defined in the text. For each simulation, the cumulative emissions (33) are set to 0 at the onset of the transition period and then linearly scaled to reach 1 by the end of the transition period (compare table S1 for actual values). This linearization is only carried out to more explicitly visualize the linearity in the models. All analyses in the paper are based on the original data shown in (A).

  • Fig. 2 Relationship between annual mean incoming shortwave radiation and sea-ice area.

    (A) Annual mean incoming top-of-the-atmosphere shortwave radiation at, and area within, a given latitude. The area within a given latitude band is calculated from simple spherical geometry. The latitudinal dependence of average daily incoming shortwave radiation at the top of the atmosphere is calculated from the very good approximation S(φ) = 1 – 0.482P2(sin(φ)), where P2 is the second Legendre polynom (34). (B) As in (A), but with the x axis exchanged for clarity.

  • Fig. 3 Relationship between Arctic sea-ice loss and other metrics.

    (A) Each dot represents the sensitivity of Arctic sea-ice loss in a particular model as a function of the increase in global mean incoming nonshortwave fluxes per CO2 emission in the same model. The latter was obtained from a linear fit of incoming nonshortwave fluxes as a function of cumulative anthropogenic CO2 emissions during the transition period of each individual model. (B) Same as (A), but fluxes only evaluated in the Arctic. (C and D) Same as (A) and (B), but neglecting sensible and latent heat fluxes. (E) Each dot represents the sensitivity of Arctic sea-ice loss in a particular model as a function of the transient climate response (24) in the same model. [See table S1 for actual values and supplementary text for more discussion on (E).] All correlations given in the figure are significant at the 1% level.

Supplementary Materials

  • Observed Arctic sea-ice loss directly follows anthropogenic CO2 emission

    Dirk Notz and Julienne Stroeve

    Materials/Methods, Supplementary Text, Tables, Figures, and/or References

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    • Materials and Methods
    • Supplementary Text
    • Figs. S1 to S3
    • Table S1
    • References

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