Page 29 - Managing Global Warming

Greenhouse gas removal and zero emissions energy production 23

informed. But plausibility cannot be capriciously determined; it must be based on the
exercise of informed judgment rooted in evidence from the past and present to accom-
modate the uncertainties and surprises of the future. Plausibility is continuously and
heuristically reconstructed.
In Section 2.5, the range of values of each independent variable is considered
through a plausibility lens. But first, without being constrained by reasonableness,
I examine the mathematical sensitivity of the two dependent variables, amounts of
GGR and ZEE, to each input parameter.

2.4 The numbers

Table 2.1 describes five scenarios, a small but indicative subset of the entire range of
putative futures. Where appropriate, results are calculated for three global temperature
increase targets, 1.5°C, 1.8°C, and 2°C. All scenarios provide that in addition to the
assumed FF emissions (including those from cement production), land use emissions
amounting to some 1.5Gt(C)/yr will continue indefinitely into the future [10]. All
these scenarios can be adapted by assuming varying degrees of increased carbon inten-
sity and reduced TFC.
No consideration is given to error ranges. The calculator produces unique mathe-
matically correct outcomes for each set of input parameters. Alternatives and sensi-
tivities can be explored by varying these input values. The purpose is not to produce a
supposedly accurate set of predictions, but to identify the scale of the policy challenge
implied by each scenario.

2.4.1 Business as usual

Under BAU, by 2100 cumulative emissions reach almost three times the 2°C carbon
budget and more than four times the 1.5°C budget. Global average temperature rise is
more than 5°C. The 1.5°C, 1.8°C, and 2°C carbon budgets are exceeded respectively
in 2029, 2039, and 2045 (Scenario 1—there are 22 scenario illustrations referred to in
the following discussion; they are shown in Box 2.2). In this scenario there is no
attempt to stay within the carbon budget.

Table 2.1 Indicative scenario groups
BAU Business as usual (BAU) assumes growth in TFC and ZEE, both following
their unabated long-term trends, with no GGR
ZEE only TFC follows long-term trend; no GGR and accelerated transition to ZEE
ZEE/REC Reduced energy demand (REC) with accelerated transition to ZEE; no
GGR
ZEE/REC/CIR Mixed portfolios of emission reduction policies; no GGR
GGR+ Combined response including GGR