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Acknowledgments DJL is funded by an RCUK fellowship. AMH acknowledges the Leverhulme
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Trust for the award of a Philip Leverhulme Prize. US received funding from the Natural Environment
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Research Council (NE/I016287/1). DJL and AMH received funding from the Natural Environment
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Research Council (NE/G009112/1).
Tables
746
∆T [◦C ] dTCO
2 [◦C ] dTorog [◦C ] dTice[◦C ] dTveg [◦C ]
Default 3.30 1.58 0.70 0.70 0.33
orography = modern 2.60 1.58 0 0.70 0.33
CO2= 350ppmv 2.71 0.99 0.70 0.70 0.33
CO2= 450ppmv 3.83 2.10 0.70 0.70 0.33
Table 1: Total mid-Pliocene global mean warming compared to preindustrial (∆T), and the global mean partitioning between CO2(dTCO2), orography (dTorog), vegetation (dTveg), and ice (dTice). This
is shown for the default case, and cases where the sensitivity to orography and CO2 are tested, as
Figure Captions
747
Figure 1: Factor separation for a function of two variables - in this case CO2and orography. (a) is the
linear approach (Equation 2), (b) is the Stein and Alpert (1993) approach (Equation 5), and (c) is our approach (Equation 7 or Equation 8).
Figure 2: Factor separation used in our study for two functions of two variables each - in this case CO2, orography, vegetation, and ice (Equation 13).
Figure 3: Orography and snow-free albedo for theE, Eoci, Eocv, and Eociv GCM simulations. For equivalent figures of the other GCM simulations (Eo, Ec, andEoc), see Table 1 of Supplementary Information of Lunt et al. (2010a).
Figure 4: (a) Simulated annual mean surface air temperature change, mid-Pliocene minus pre- industrial,∆T. (b-e) Surface air temperature changes due to (b) CO2(dTCO2), (c) orography (dTorog),
(d) vegetation (dTveg), and (e) ice (dTice); as calculated from Equation 13.
Figure 5: Zonal annual mean surface air temperature changes due to CO2(dTCO2), orography (dTorog),
vegetation (dTveg), and ice (dTice) [◦C ].
Figure 6: Surface air temperature change due to CO2 alone calculated as (a) Equation 2 and (b)
Equation 3. The difference between the two approaches (equal to the synergy, S in Equation 5) is shown in (c).
Figure 7: (a) Difference in mid-Pliocene surface air temperature between our simulation and that of Haywood and Valdes (2004). (b) The same, but for the mid-Pliocene anomalies, mid-Plioene minus pre-industrial.
First quantification of the relative influences on mid-Pliocene warmth and polar amplification of CO2, orography, vegetation, and ice sheets.
A new factorisation technique, an improvement on the traditional Stein+Alpert approach.
A quantitative assessment of the uncertainties in our results.
T Toc Tc orography CO2 dTco2=Tc−T dTorog=Toc−Tc (a) T Toc Tc orography CO2 dTco2=Tc−T To dTorog=To−Tc S=Toc−To−Tc+T (b) T Toc Tc orography CO2 To dTorog=1/2((To−T)+(Toc−Tc)) dTco2=1/2((Tc−T)+(Toc−To)) (c) 1 Figure 1
orography CO2 dTorog=1/2((To−T)+(Toc−Tc)) dTice=1/2((Toci−Toc)+(Tocvi−Tocv)) T Toc Tc To dTco2=1/2((Tc−T)+(Toc−To)) Tocv Tocvi Toci dTveg=1/2((Tocv−Toc)+(Tocvi−Toci)) ice vegetation 1 Figure 2
Exp. orography [m] snow-free albedo E Eoci Eocv Eociv 1 Figure 3
(a)
(b) (c)
(d) (e)
1
Figure 4
-50 0 50 latitude -5 0 5 10
surface air temperature anomaly [degrees C]
DT dTco2 dTorog dTveg dTice (a) -50 0 50 latitude -5 0 5 10
surface temperature anomaly [degrees C]
GCM EBM
emissivity due to clouds emissivity due to greenhouse gases albedo due to clouds
albedo due to planetary surface due to heat transport
(b)
1
Figure 5
(a) (b) (c)
1
Figure 6
(a) (b)
1
Figure 7
Supplementary material for on-line publication only