Four degrees and beyond: the potential for a global ... - Amper

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Cumulative carbon emissions 61 2200 has a cumulative total of 0.3 TtC, which leaves only 0.2 TtC remaining if the pathways are to have a cumulative total of 1 TtC. This forces the emissions profile to have a high rate of decline, which could make these profiles socio-economically unfeasible [21]. (d) Constraining the rates of warming Thus far, we have only considered constraints on peak levels of global warming. A key objection to using peak warming targets in isolation is that the feasibility and cost of adapting to future climate change will also depend strongly on the rate of change and not just on the magnitude of global warming. In order to determine which factors constrain the maximum rate of warming, we use the same model experiments as reported in figure 2. Thus, we use only best-guess or most likely ensemble members, and we only consider emissions profiles with zero emissions floors. We now plot the peak rate of CO2-induced warming as a function of the emission metrics, as illustrated in figure 5. In figure 5, we find a very different set of correlations from those presented in figure 2. The main result, across all the panels in figure 5, is that the tightest linkage is between the peak rate of warming and peak emission rate. We now explain these results in more detail. Though cumulative carbon emissions have a tight correlation with peak warming, figure 5a shows that they share only a very weak correlation with the peak rate of warming. The maximum rate of warming is instead controlled by the peak rate of emission, as indicated in figure 5f . The gradient of the points in figure 5f suggests that, for each extra GtC yr −1 on the peak emission rate, the best-guess maximum rate of warming will increase by 0.016 ◦ C per decade. It is known, however, that short-lived non-CO2 greenhouse gases, such as methane, which we do not include in this paper, also influence atmospheric radiative forcing [34]. Although these gases have shorter lifetimes than CO2 [34], they still have the potential to influence rates of warming beyond that induced purely by CO2. Figure 5a shows only a slight correlation, which occurs because the peak rate of emission and the cumulative emissions are not completely independent. Consider two emission pathways with different peak rates of emission and the same rate of emissions decline after the peak: the pathway with the higher peak will lead to a higher cumulative total, as shown in figure 5. As we cap the maximum rate of emissions decline to 10 per cent per year, higher peak emission rates will have a bias towards larger cumulative totals, which explains the correlation we observe in figure 5a. The grey diamonds in figure 5 represent emission pathways that have a maximum rate of emissions decline of between 4 and 10 per cent per year, while the black crosses correspond to rates of decline between 0 and 4 per cent. For pathways with a cumulative total of less than 1 TtC and a rate of decline of less than 4 per cent per year, figure 5 shows only a limited range of possible rates of warming. This limited range of pathways all have a rate of warming less than 0.2 ◦ C per decade, which initially suggests that a cumulative emissions target could be used to constrain rates of warming, assuming that rates of decline are Phil. Trans. R. Soc. A (2011) Downloaded from rsta.royalsocietypublishing.org on November 30, 2010
62 N. H. A. Bowerman et al. (a) 0.30 peak warming rate (ºC per decade) 0.15 0 1 2 3 cumulative emissions from 1750 (TtC) (c) 0.30 peak warming rate (ºC per decade) 0.25 0.20 (b) (e) 0.30 (f) peak warming rate (ºC per decade) 0.25 0.20 0.25 0.20 1.5 TtC 1.3 TtC 1.1 GtC yr –1 3.1 GtC yr –1 24 years 17 years 17 years 1.0 TtC 24 years 1.0 TtC 1.1 GtC yr –1 1.2 GtC yr –1 5 10 15 20 2020 emissions (GtC yr –1 0.15 ) 0.15 1980 2000 2020 2040 2060 2080 year of peak emissions (year) 0.26 TtC 0 0.2 0.4 0.6 0.8 cumulative emissions 2010–2050 (TtC) (d) 0.5 GtC yr –1 0.19 TtC 13.4 GtC yr –1 10.1 GtC yr –1 1.0 GtC yr –1 0.5 GtC yr –1 0.20 TtC 7.7 GtC yr –1 0.07 TtC 6.7 GtC yr –1 0 5 10 15 20 25 2050 emissions (GtC yr –1 ) 1.0 GtC yr –1 5 10 15 20 25 peak emissions (GtC yr –1 ) Figure 5. The correlation of emission metrics with most likely peak warming rate. This figure is like figure 2, but plotting against peak rate of warming instead of against peak warming. Again, black crosses indicate emission pathways in which the maximum rate of emissions decline is less than 4% yr −1 ; grey diamonds indicate the converse. The bars show the spread of the metrics for pathways with a resultant peak rate of warming of 0.2 ◦ C or 0.25 ◦ C. The black bars show the spread in pathways with peak rates of emissions decline less than 4%, while the grey bars show the spread in all emission pathways. We see that the strongest correlation is in (f ), between peak rate of warming and peak emission rate. Phil. Trans. R. Soc. A (2011) Downloaded from rsta.royalsocietypublishing.org on November 30, 2010
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ISSN 1364-503X volume 369 number 19
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Phil. Trans. R. Soc. A (2011) 369,
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Editorial David Garner Phil. Trans.
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Four degrees and beyond: the potent
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Preface 5 commitments might give us
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8 M. New et al. In the final plenar
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10 M. New et al. supports the messa
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(a) number of models, black line nu
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change in run-off (%) change in run
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Water availability in +2 ◦ C and
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Water availability in +2 ◦ C and
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Agriculture and food systems in sub
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118 P. K. Thornton et al. 1. Introd
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120 P. K. Thornton et al. increases
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122 P. K. Thornton et al. Table 1.
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124 P. K. Thornton et al. century.
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126 P. K. Thornton et al. and polit
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136 P. K. Thornton et al. 83 Challi
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Humid tropical forests on a warmer
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(a) Humid tropical forests on a war
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0 retraction risk 17 120 80 40 (a)
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0 retraction risk 17 120 80 40 0
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Sea-level rise and its possible imp
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162 R. J. Nicholls et al. expected.
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164 R. J. Nicholls et al. sea-level
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REVIEW Phil. Trans. R. Soc. A (2011
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Review. Interactions in a 4 ◦ C w
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spread in mosquitoborne disease may
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[89,94,95] further acidification by
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Editorial Editorial 3 D. Garner Pre
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