Can biofuels help with climate change?

The book Climate Change: Biological & Human Aspects (Cambridge U. Press) covers many aspects of 'global warming' including energy options. One such option is to use biofuels rather than fossil fuels, but is this a realistic option?

The below is a single extract (p385-387) from Climate Change: Biological & Human Aspects (1st edition 2007): just one of the book's number of references to a range of energy strategy options and several mentions of biofuels.

As to the potential contribution of biofuels, taking the UK as an example, if all 500,000 ha of UK set-aside land (this is equivalent to 3% of the land within agricultural holdings) was planted with, for instance, Miscanthus, and assuming a median dry matter production of 15 t/ha per year and a broadly typical 40% conversion to oil in energy-content terms, then some 3 mtoe (million t of oil equivalent) of biofuel would result. This would be equivalent to nearly 4% of the UK annual oil demand. If Miscanthus oil production could be increased to an optimistic 25 t of dry matter/ha, then over 6% of UK oil demand would be met. However, Miscanthus does not reach its peak yields until the third or fourth season, even though absolute peak yields for Miscanthus sacchariflorus of 44 t of dry matter/ha per year have been reported from Denmark. This peak, if possible across all such potential UK Miscanthus production, would result in 14 or 15 t of oil/ha per year. However, such high yields are highly theoretical and cannot be considered a realistically obtainable national average at this time (Cowie, 2003), although they might with appropriate breeding or genetic modification if environmental concerns could be addressed.

      A similar calculation for oilseed rape would take into account the approximately 3.2 t harvested per hectare (in the UK), the 37% of recoverable oil from the rapeseed and the 95% conversion to diesel. This gives us about 0.4mtoe/ year (0.5% of UK oil demand). The advantages of rape are that the plant's entire life cycle takes place in the UK, but has the disadvantages that methanol (equivalent to about 12% of fuel yield) is required during the diesel-making process: however, this methanol could come from biological sources too. It should be noted that there are rotational constraints on rapeseed production: rapeseed is usually grown one year in five in the UK.

      Miscanthus and rapeseed oil are taken as just two examples of how currently unused set-aside land could contribute to make the UK more energy-secure through increasing energy self-sufficiency. However, it may be that some other crops, or crop mix, would be preferable. Climate conditions do not favour Miscanthus rhizome production in Europe as they do in the tropics. Nonetheless, rhizome production is possible in the UK (which is warmed by the Gulf Stream) and in some other parts of Europe. Consequently, the examples are illustrative and the production levels of' Miscanthus and rapeseed oil are not atypical in energy terms of other biofuels.

      It should be noted that in addition to the 3% of land within agricultural holdings being set aside, 97% is not. (Of this 24% is rough grazing and 11% unspecified. Indeed, of the 97% of agricultural land that is not set aside, only 25% is used for crops.) In short, there is room for some considerable increases in the land that might be available for biofuels. Assuming, solely for purposes of example, that 6% of current UK oil consumption was met through the use of specific biofuel crops, then there is the additional possibility of a biofuel contribution from dependent sources: that is, crops that are grown for other purposes; for example, straw (as mentioned above) or crop trimmings, such as from field vegetables. This last is currently on land covering over eight times the size of set-aside land. Indeed, much of the above-ground biomass that is not harvested for food or export (the waste biomass) from these species could be used for biofuel production. Finally, there are the biofuels available from forestry and woodland, such as from short-rotation coppicing.

      In 2002 the Institute of Biology ran a biofuels workshop in London as part of an energy series run also by the Institute of Physics and Royal Society of Chemistry, which was sponsored by the Department of Trade and Industry. Workshop participants, all associated with either the biofuel industry or biofuel research, were asked in advance as to the potential for biofuels to offset UK oil demand. The modal answer was around 20 5% of UK oil demand or about 7% of total UK primary energy consumption. If this estimate is realistic then it represents some 16 million t of UK domestic annual oil consumption and a roughly a 1.3 billion gain to the UK's domestic economic output at the point of refinement/production (not point of sale) in terms of crude-oil savings. This 7% figure of UK primary energy goes a long way towards meeting the Government's medium-term renewable targets, although the UK will require greater displacement of fossil fuel than that if it is to meet its Kyoto targets. Even so, it is difficult to see any fossil-fuel-reducing strategy in the medium-to-long term in the UK that does not include biofuels (Cowie, 2003).

      The estimate for a practical biofuel contribution to the UK of some 15-25% of current oil consumption, or 7% of UK primary energy, is not at all unrealistic. True, while a greater proportion may well be feasible, equally it might perhaps incur significant opportunity costs (probably either to strategic food production and/or the environment). The importance of biofuels to the UK would be best appreciated if undertaken as part of a coherent energy strategy, along with improved energy efficiency as well as changes of behaviour favouring lower energy consumption. The question is whether the UK Government would consider a firm drive for biofuels to be a worthy goal in economic, environmental and strategic terms. It is also a question other governments will need to face. The concerns raised by the workshop that the UK was not coherently exploring biofuel options were subsequently echoed by a House of Commons Select Committee report (EFRA Select Committee, 2003; See also the UK policy case history in Chapter 8).

      Finally, the 2002 Institute of Biology biofuels workshop looked at costs. The range of figures presented did result in an end biofuel cost per barrel that was of the same order of magnitude as that for crude oil (which still has refining costs to bear). Unfortunately the current vagaries of small-scale production, lack of distribution and other factors made a firm costing difficult. Nonetheless, biofuels remain a useful option as part of a suite of measures to counter fossil-fuel emissions of carbon dioxide.

      Globally, aside from non-commercial local use of biofuels (see section 8.2.3) a little over 1% of commercially traded energy currently comes from biomass. Of all countries, Brazil arguably leads in biofuel production and consumption with biofuels contributing some 20% of its primary energy supply. (However, questions need to be asked as to how much of this comes from biologically sustainable sources that do not contribute net greenhouse emissions from climate change). While biomass could theoretically make a major contribution to offsetting fossil-fuel consumption it is more likely to be used to meet chemical feedstock demand as oil becomes more expensive, especially as there are competing land pressures for food production. It has been calculated that if, for example, the USA were to displace 10% of its car petrol consumption with biofuel then 12% of US cropland would be required, but a further 38% would be needed (bringing the total to nearly 50% of currently available cropland) once the energy requirements for processing, harvesting and transportation are taken into account (Kheshgi et al., 2000). Consequently it is only likely that commercial biofuels could possibly make a small but significant contribution to meeting future energy needs within an early to mid twenty-first-century window of opportunity (see Table 8.2) before the preference tends to food production.

 

Climate Change: Biological & Human Aspects is available from Cambridge University Press, Cambridge UK and its offices overseas including in New York (US), Melbourne (Australia), Madrid (Spain), Cape Town (South Africa) and elsewhere. ISBN 978-0-521-87399-4 (hardback) and ISBN 978-0-521-6919-7 (paperback). See also details at CUP.   It is illustrated with around 70 diagrams and a score or so of tables. It is fully referenced and has a number of explanatory appendices. Aimed at those with differing expertise, it is an introductory text but (being in a large-sized format and at around 500 pages) comprehensively covers a wide range of climate-related issues.

Click to purchase page Climate Change: Biological & Human Aspects 2nd edition (2013).

Eos: Transactions of the American Geophysical Union book review of Climate Change: Biological and Human Aspects

 

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