Page 24 - Managing Global Warming

Greenhouse gas removal and zero emissions energy production 19

Box 2.1
Notation SI equivalent Description
9
15
Gt Gt (10 tor10 g) Gigatonne or 1000 million tonnes
Gt(C)/yr Gt(C) a 1 Gigatonne of carbon per year
Gt(CO 2 )/yr Gt(CO 2 )a 1 Gigatonne of carbon dioxide per year
ppmv Parts per million by volume
Quadrillion 10 15 1 million billion
1M km 3 10 15 m 3 1 million cubic kilometers
3 1
9
3
1km /sec 10 m s 1 cubic kilometer per second
1M km 2 10 12 m 2 1 million square kilometers
About or approximately
6
MJ 10 J Megajoule (1 MJ¼0.2778 kWh)
EJ 10 18 J Exajoule (1 EJ¼277.78 MWh)
EJ/yr 10 18 Ja 1 Exajoules per year
Btu British thermal unit (1 Btu¼0.293Wh)

radiative forcing that would correspondingly increase the requirement for GGR and/or
ZEE [2]. It is unclear at present how the additional radiative forcing from ocean
outgassing [3] might be different for GHGs avoided and those removed.
The relationship between global temperature change and total cumulative anthro-
pogenic CO 2 emissions (TCRE) has been shown to be near linear for cumulative
emissions at least to 2000Gt(C). The current best estimate is that limiting global
warming relative to the period 1861–80 to less than 2°C with greater than 66% proba-
bility will require cumulative CO 2 emissions since 1870 to not exceed 1000Gt(C) ([4]:
Section 12.5.4.3). This analysis uses these values as the benchmark for the simulation
of the emissions scenarios for different temperature targets.
The TCRE methodology is concerned only with CO 2 emissions. Non-CO 2 GHGs
represent about one-third of the anthropogenic radiative forcing, and of this half is
produced by methane, a short-lived GHG [5]. While these GHGs are climatically sig-
nificant, even their complete removal from the atmosphere would not obviate a need
for the removal of large amounts of atmospheric CO 2 , which could only be delivered
by radical changes to the global FF energy economy. Accordingly, because the policy
implications of these changes are the primary focus of this chapter, non-CO 2 GHGs
are ignored in this analysis. The IPCC estimates that accounting for non-CO 2 GHGs
would reduce the carbon budget from 1000 to 790Gt(C) ([4]: Section 12.5.4.3).
This would make even greater both the scale and the urgency of the need for GGR
identified in this chapter.
Long-term historical data for global energy consumption and emissions are extra-
polated to 2100 using policy relevant variables. These variables, using averaged
global values, include the timing and extent of the transition away from FF, reductions
in TFC, and incremental improvements in energy efficiency. The dependent variables
are the ZEE required to meet future energy demand, and where necessary, the GGR
needed to remain within the available carbon budget. The extrapolations of historical
data are used as benchmarks from which to assess the scale of change implied by