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A GLOBAL OUTLOOK ON METHANE GAS HYDRATES
17
In 1985, Marchetti presented the concept of the hydrogen to
carbon ratio (H/C), which can be used as a proxy for environ-
mental quality (Marchetti 1985; Ausubel 1998). Firewood has
the highest carbon content and lowest H/C ratio, with about
one hydrogen atom per ten carbon atoms. Among fossil ener-
gy sources, coal has the lowest H/C ratio at roughly one hydro-
gen atom to one carbon atom. Oil has, on average, two hydro-
gen atoms to one carbon atom, and natural gas or methane,
four hydrogen atoms to one carbon atom. Figure 1.4 shows the
changes in the H/C ratio resulting from global primary energy
substitution in the period from 1860 to 2009 and the continu-
ous decarbonization from 1860 to 1970. At this point, the H/C
ratio has become approximately constant.
Many energy analysts agree that this trend points to a future
increasingly fuelled by natural gas, which could serve as a
bridge towards a low- to no-carbon long-term energy outlook
(Nakicenovic
et al.
, 2011; MIT 2010). That is consistent with
the dynamics of primary energy substitution, as well as with
the steadily decreasing carbon intensity of primary energy and
the increasing hydrogen to carbon ratio.
As non-fossil energy sources are introduced into the primary
energy mix, new energy conversion systems will be required
to provide low- to no-carbon energy carriers, in addition
to growing shares of electricity. Ideal candidates might be
conversion systems with carbon capture and storage tech-
nologies. With the implementation of such technologies, the
methane economy would lead to a greater role for energy gas-
ses and, over time, hydrogen. An analysis of primary energy
substitution and market penetration suggests that natural
gas could become the dominant energy source and that the
methane economy could provide a bridge toward a carbon-
free future (Grubler and Nakicenovic 1988, IPCC 2007).
1860 1880 1900 1920 1940 1960 1980 2000
0
0.1
1
10
100
Percent (logarithmic scale)
Share in total primary energy
Traditional
biomass
Coal
Oil
Gas
Nuclear
Renewables
Sources:WEC, 1998; IEA, 2012; Grubler and Nakicenovic, 1988.
Source: Marchetti, 1985;WEC, 1998 and IEA, 2012
1800
1850
1900
1950
2000 2050
2100
0
0.1
1
10
100
Hydrogen to carbon ratio of global
primary energy
Gas H/C = 4
Methane age
Oil age
Coal H/C = 1
Coal age
Pre industrial age
Wood H/C = 0.1
Carbon free age
Oil H/C = 2
1860
1935
1970
Percent (logarithmic scale)
Figure 1.3:
Global primary energy substitution 1860-2009,
expressed in fractional market shares. Sources: WEC (1998), IEA
(2012), Grubler and Nakicenovic (1988).
Figure 1.4:
Hydrogen to carbon ratio of global primary energy, 1860-
2009. The ratio is expressed in fractional shares of hydrogen and
carbon in average primary energy consumed. Source: Marchetti
(1985), WEC (1998), IEA (2012).