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Greenhouse gas removal and zero emissions energy production 47

2Gt(C)/yr rather than 1Gt(C)/yr (Scenario 5), or peak emissions being deferred for
5 years to 2025. These variations make no appreciable difference to either cumulative
emissions by 2100 or the demand for ZEE during the remainder of the century.
In the BAU scenario, the same energy demand reductions reduce cumulative emis-
sions to 2100 by 40%. However, they still exceed the 1.5°C,1.8°C and 2°C carbon
budgets by 117%, 81% and 63% respectively; there is no impact on the ZEE Index
that remains at 1.

2.4.4 Zero emissions energy/Reducing energy consumption/
Carbon intensity reduction

Adding CIR (carbon intensity reduction) into the policy mix renders the targets less
demanding. CIR refers specifically to reducing emissions from using FF by switching
from high emitting to cleaner FF, for example from coal to natural gas. (Reducing
emissions by replacing FF with ZEE is included in ZEE and not in CIR.) Moreover,
CIR refers to the incremental reductions in carbon intensity beyond those subsumed in
the long-term historical trend. The long-term changes in the shares of coal, oil, and gas
are already reflected in the historical correlation between TFC and emissions (Fig. 2.4
infra), and therefore the continuation of these benefits is equally reflected in their
extrapolations into the future. To avoid double counting, the CIR must be limited only
to incremental improvements beyond those subsumed in the historical data.
Although carbon capture and storage (CCS) has the practical effect of reducing the
carbon intensity of the fuels being combusted, because it also involves the capture and
sequestration of carbon, in this chapter it has been included among NETs (see discus-
sion in Section 2.5).
In the extreme case of BAU, CIR must begin in 2018 and reach 98% within 20 years
to achieve the 1.8°C target (Scenario 6) (93% for 2°C, 1.5°C is unachievable). This is a
world in which technology is focused almost entirely on reducing the emissions from
the growing consumption of FF, rather than on replacing them with ZEE. Adding
reductions in energy consumption has minimal additional impact. As will become
apparent in Section 2.5, this is not a plausible future.
Bringing some CIR into the mix makes the targets less challenging in terms of
other policy actions. For example, the 1.8°C target could be met by combining
emissions peaking in 2025 and falling to 2Gt(C)/yr in 25 years, TFC reductions
commencing in 2018 and reaching 40% within 30 years, and CIR starting in
2018 and reaching 70% in 20 years (Scenario 7). If the emissions fall instead to
1Gt(C)/yr, the requirement for CIR can be reduced to 55%. In these scenarios
the ZEE Index is 8.

2.4.5 Greenhouse gas removal
In theory, any excess in cumulative emissions can be removed by GGR. For example,
for BAU even the 1.8°C target can be met by 2100 with GGR commencing in 2050 and
increasing over 30 years to 52Gt(C)/yr (Scenario 8). However, while this scenario