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sumption of more plant based foods (Stehfest et al. 2009 ; Pierrehumbert and Eshel
2015 ). The RCP 4.5 scenario (Thomson et al. 2011 ) projects a CH 4 mixing ratio of
1.80 ppm in 2060 (Table 4.2; Fig. 4.12), close to today’s value. The RCP 4.5 design
entails the use of a market pricing mechanism to stabilize global emissions of CH 4
(and CO 2 , as well) at close to present level. Finally, the RCP 8.5 projection has
atmospheric CH 4 at 2.7 ppm in 2060 and continuing to rise, unabated, until end of
century (Fig. 4.12).
As noted in the introduction, the transition of production of electricity from coal
to natural gas^32 is touted by many as being climate friendly because combustion of
(^32) We use natural gas and methane interchangeably, but we are well aware that the mixture of gas
burned in a so-called natural gas facility does contains trace amounts of hydrocarbons other than
methane. Indeed, the association of ethane with methane in atmospheric samples can help distin-
guish whether a pulse of methane is due to ruminants or industry.
a
bc
Fig. 4.12 Impact of CH 4 on EM-GC projections using RCP 4.5. (a) Time series of atmospheric
CH 4 from observations (Dlugokencky et al. 2009 ), RCP 4.5 (blue, lowest curve) (Thomson et al.
2011 ) and RCP 8.5 (red, highest curve) (Riahi et al. 2011 ) as well as various other “blended” sce-
narios for CH 4 that are linear combinations of RCP 4.5 and RCP 8.5; (b) probability that the rise
in ΔT in 2060 stays below 1.5 °C (gold diamonds) and 2.0 °C (blue squares) relative to pre-
industrial, computed using RCP 4.5 combined with one of the blended CH 4 scenarios and plotted
as a function of CH 4 in 2060; (c) same as (b), except for year 2100
4 Implementation