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Greenhouse gas removal and zero emissions energy production 55

given that 30% of energy consumption is already from natural gas and ZEE, the theo-
retical upper bound for reduced emissions is about 35%. I propose a range of plausible
values for CIR between 0% and 25%.

2.5.4 Greenhouse gas removal (GGR)

An important distinction must first be made between carbon capture and storage
(CCS) of FF emissions and CCS of biomass emissions. CCS of FF emissions is not
a NET because the GHGs already in the atmosphere remain there. CCS applied to bio-
mass combustion is a NET, the most discussed of which are BECCS (bioenergy CCS)
and biochar (the production of charcoal for incorporation into the soil). Despite CCS
of FF emissions not being a NET, it does require the capture and sequestration of the
emitted GHGs. These processes compete for resources with genuine NETs and there-
fore when considering the plausibility of these technologies, it is useful to
combine them.
The key dependent variable from this calculator is the annual amount of GGR,
measured in terms of gigatonnes of carbon to be sequestered to meet the chosen tem-
perature target in the relevant scenario. For GGR, the two independent variables are
the year in which it commences and the period in years taken to reach the calculated
annual amount of sequestration. Given that GGR technologies do not yet exist in any
scalable form, it will require concerted action by policymakers before their deploy-
ment can begin in earnest. I suggest this is implausible prior to 2025, and even this
timing assumes considerable investment in research and development in the immedi-
ate future.
The second variable is the rapidity with which GGR is up-scaled after its com-
mencement. This will also be policy rather than market dependent because the scale
at which GHGs must be extracted for climate relevance exceeds any likely market
capacity for them. Again, this may change if any currently nascent technologies
emerge with unexpected potential. However, the time it would take the capacity of
these markets to reach the necessary scale makes it relatively unlikely that they will
be able to make a major contribution to meeting the climate targets (refer to Fig. 2.4).
The time it takes for GGR to be scaled is likely to be longer, the higher its eventual
level. The minimum plausible period I propose is illustrated in Fig. 2.6.
All approaches to GGR entail two core processes: the capture of GHGs from the
free atmosphere, and their sequestration in secure and permanent storage. While at
laboratory, and even at industrial scale, there is already a considerable body of expert-
ise with both, their scale is more than two to three orders of magnitude smaller than
current global CO 2 emissions [21,22]. To grasp the scale, consider current annual
emissions of 35Gt(CO 2 )/yr (containing 10Gt(C)). This CO 2 is contained within
3
3
45 10 15 m (45Mkm ) of air (assuming 400ppmv at 1atm and 20°C). Processing
3
air at 1km /sec (assuming 100% efficiency) would remove 70% of current emissions
3
and would, for example, produce 32km of liquefied CO 2 or 70GtMgCO 3 if miner-
alized. These are quantities of material that are one or two orders of magnitude greater