So, having looked at the need for equivalent boundaries in life cycle analysis and the different results that can be found from similar methodologies but within different envelopes, it’s possibly time to look at some of the more complicated issues. Perhaps the most complicated of these is how do deal with Land Use Change (LUC), both direct and indirect.
Direct Land Use Change is relatively simple to account for, although the measurement of changes to carbon stocks, sequestration rates and whether land use for the production of bioenergy feedstocks should be treated differently to any other types of land use (food production is the one most often cited, but really all uses, including conservation, pharmaceuticals, social goods, etc. should all be taken into account).
However, even if we ignore the can of worms that is Indirect Land Use Change (ILUC) for a moment – and it is just a moment, I promise – there is still the issue of how much land is available for bioenergy production. In fact there are as many different estimates as there are people asking the question, a factor further complicated by the numerous definitions of agricultural land, marginal land, degraded land, etc. etc…
One of the latest estimates just published in Environmental Science & Technology has used satellite imaging to estimate the ‘Bioenergy Potential of the United States Constrained by Satellite Observations of Existing Productivity.’ The authors have found that the primary bioenergy potential (PBP) of ‘of the conterminous U.S. ranges from roughly 5.9 to 22.2 EJ yr–1, depending on land use. The low end of this range represents the potential when harvesting residues only, while the high end would require an annual biomass harvest over an area more than three times current U.S. agricultural extent.’
Furthermore they conclude that meeting current US bioenergy targets with existing technology ‘would require either an 80% displacement of current crop harvest or the conversion of 60% of rangeland productivity.. More on this paper can be found at CattleNetwork.
As the ‘ethanol land use debate continues’ it won’t just be biofuels that are increasing demand for vegetable oils and other feedstocks. Politicians will need to make careful policy decisions to balance the demands of food and fuel production, as well as other effects on wildlife and biodiversity and water. But blaming bioenergy alone for these pressures is overly simplistic. They have existed ever since man settled down and began agricultural production. The only difference is that today, we have nowhere else to move to when we run out of resources. That said, some studies, such as a recent one in Washington State, predict plenty of biomass to go round for some time yet.
Enagri is the only weekly publication dedicated to bionergy in the UK.