Thanatia and the Crepuscular Earth Model - Thanatia: The Destiny of the Earth's Mineral Resources - page 298

Table 10.1 Mass of carbon stored in fossil fuels. Values are given in GtC (10 15 gC) (Valero
et al., 2011)

Proven reserves Estimated additional reserves Total

Conventional fuels 724.8 1,250.81 1,975.61

Non-conventional fuels 1,200.2 13,048.49 14,248.69

Total 1,925.01 14,299.3 16,224.3

Table 10.2 Emissions scenarios (Valero et al., 2011)

Scenario Reference data CUE (GtC)

BAU-I Historical 2,265

BAU-II Historical 16,564

A2-II SRES A2 16,564

is also evident from Table 10.1 that the total non-conventional fossil fuel stocks are
much greater (by about sevenfold) than the conventional ones. But the commercial
production of fossil fuels depends on many other factors, not just reserves, since it
is subject to restrictions such as technological development, economic conditions,
legal constraints and social acceptability amongst others (Höök et al., 2010b). This
adds uncertainty to the accuracy of the estimation of future emissions.
The third ingredient needed in the determination of the crepuscular atmosphere
is the selection of an appropriate emission scenario to forecast the rate of emissions
due to the future consumption of fossil fuels. Such scenarios are developed by fitting
a logistic-type curve to reference data for emissions (Nel and Cooper, 2009) and
involve the use of cumulative ultimate emissions (CUE). A term used to define the
amount of carbon that has been already emitted from the time of the preindustrial
era (taken as 1750), which is about 340 GtC (Marland et al., 2008), plus the quantity
of carbon to be emitted in the future. Valero et al. (2011) use two figures for
the CUE, corresponding to the values of proven and total reserves (proven plus
estimated) as provided in Table 10.1. Where only proven reserves are considered,
scenarios are denoted as -I, and consequently where total reserves are considered,
the scenarios are denoted as -II. Valero et al. (2011) also use two sets of reference
data to fit the logistic curve. The first set consists of the historical carbon emissions
derived from fossil fuel combustion for the period 1750-2007 whilst the second is the
land-use emissions for 1750-2005 (Marland et al., 2008). These scenarios are referred
to as “business as usual” (BAU) . The reference data used for the other scenarios
are the carbon emissions from IPCC SRES A2 scenario (Nakicenovic and Swart,
2000). This was selected because it is likely to describe a “worst case” projection of
future emissions since it considers a very heterogeneous world with a continuously
increasing population (Höök et al., 2010b). Table 10.2 describes the scenarios used.
The rate of emissions corresponding to these scenarios is presented in Fig. 10.2.
Finally, the carbon cycle model was run for each of the three scenarios. Fig. 10.4
shows the temperature anomaly corresponding to the CO 2 trajectories of Fig. 10.3,