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60 Managing Global Warming

retired so rapidly, reductions in energy consumption (REC) and transitions to low
emissions FF (CIR) have little impact on cumulative emissions although they do
reduce significantly the requirement for ZEE. The rapid reduction in emissions must
therefore be accomplished in parallel with building ZEE resources to fill the vacated
energy space. The implications for ZEE are considered in Section 2.7. This policy
complex requires resolute and urgent action for it to be deliverable.

2.6.2 GGR of 1.5Gt(C)/yr
With GGR starting in 2025 and building to 1.5Gt(C)/yr within 17 years, the 1.8°C
target can be met if FF emissions peak in 2020 and fall to 2Gt(C)/yr by 2054 with
a modest contribution of 5% from CIR by 2040. In this scenario, no assistance is
needed from REC (Scenario 14).
However, even with maximum support from CIR (implying a concerted global
shift to replace coal with natural gas), the 1.5°C target can only be met if FF emissions
have already peaked and are reduced to zero in 40 years (Scenario 15). In this scenario,
the GGR target must be reached in only 10 years, and even maximum REC makes no
material difference to cumulative emissions although it does reduce the ZEE Index
from 14 to 11.
The 2°C target is achieved with 1.5Gt(C)/yr of GGR by 2042 and a more gradual
decline in FF emissions to 4Gt(C)/yr within 40 years together with modest assistance
from CIR of 3% achieved over 25 years. Plausible TFC reductions (REC) are too small
to have a material impact on these outcomes; however, REC of 20% achieved in
10 years from 2017 would reduce the ZEE Index from 13 to 10.
If, on the other hand, FF emissions do not peak until 2025, to deliver 2°C with no
more than 1.5Gt(C)/yr of GGR by 2035, emissions must stabilize at 2 rather than 4Gt
(C)/yr within 40 years. The ZEE Index remains at 14. If this scenario is enhanced by
TFC reductions of 20% over 20 years, while the impact on emissions is negligible, the
ZEE Index reduces to 11, considerably less demanding than 14 but still a challenging
growth target. The requirement for GGR also reduces to 1.1Gt(C)/yr (Scenario 16).
Alternatively, the growth in GGR could be slowed to reach a peak of 1.5 Gt(C)/yr by
2065.
GGR of 1.5Gt(C)/yr allows policymakers more flexibility in reducing FF emis-
sions, but they must still have peaked within the next decade and reduce to close
to zero within 50 years. REC has almost no impact on cumulative emissions because
to keep the requirement for GGR at or below 1.5Gt(C)/yr, the reduction in emissions
must be so fast that accelerating it further produces only a modest additional advan-
tage. While CIR allows residual emissions to settle at a higher level, this is a chime-
rical advantage since it merely shifts exceeding the carbon budget into the early part of
the next century. The ZEE Index in all these scenarios is more than 10. However, the
bulk of this ZEE is required from 2040 onwards, giving policymakers a couple of
decades to lay the foundations for increased ZEE resources at the necessary scale
(see Section 2.7).