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224 Managing Global Warming

did not foresee any drop in CO 2 energy emissions by 2035. Bioliquids for transport
would also remain marginal, rising from 3.1 to only 5.4EJ over the period. Similarly,
the US Energy Information Administration (EIA) projected global energy-related CO 2
emissions to continue to grow at 1.0% per year over the period 2010–40 [13]. Annual
fossil-fuel use was likewise projected to continue to rise.

6.2 Biomass energy

6.2.1 Introduction
Bioenergy is by far today’s leading RE source, but most consumption still takes the
form of fuelwood, crop residues, and animal dung burnt at low efficiency in industri-
alizing countries. Only about 4.3EJ of the estimated total global consumption of 59EJ
is from modern forms of biomass, comprising liquid fuels (ethanol and diesel) for
transport vehicles and fuel for electricity production, including bagasse burnt to pro-
vide power in cane sugar refineries [4,5,14].
Biomass is unique among RE sources in that, like fossil fuels, its energy is mate-
rially embodied. It can thus be stored and used at any time, unlike other RE sources
such as wind or solar, which exist only as energy flows. Biomass is also different, at
least in extent, from other RE sources in that its basic inputs of fresh water and fertile
(and relatively flat) land, face increasing competition from other uses of biomass,
namely, from agriculture (food, fodder for livestock, fibers such as cotton) and for-
estry (construction timber and products, fiber for paper, etc.).

6.2.2 Bioenergy in 2050

Bioenergy is the oldest form of nonfood energy, with its origins perhaps 500,000years
ago. Chances for further major technical breakthroughs in combustion appear small,
with most research now concentrated on topics such as increasing crop productivity
and converting cellulosic materials to liquid fuels for transport. At present, all such
liquid fuels are derived from edible feedstocks—grains, sugar, and edible oils—which
raises ethical questions in a world with an estimated 800 million people facing abso-
lute food shortages [15]. The present effort put into cellulosic conversion may be mis-
placed: from an energy or GHG reduction viewpoint; it is better to use biomass
directly to produce electricity, particularly if it displaces coal or oil as power plant
fuels, rather than convert it to liquid fuels for transport [16].
Global land-based Net Primary Production (NPP) is the total mass of living plant
matter produced annually, minus plant respiration. Terrestrial NPP, estimated at
2000EJ [17], obviously fixes a theoretical upper limit on the human appropriation
of NPP (HANPP). Estimates for global HANPP vary, depending upon which items
are included or excluded, with values ranging from 10% to 50% [18]. Since nonhuman
nature provides ecosystem services (apart from obvious ones like food and timber) on
which we are dependent, any major rise in HANPP could merely be trading growth in
one set of ecosystem services (e.g., food) with a corresponding loss in others