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Crop-based biofuels as a sustainable energy solution: The importance of life cycle assessment

Written by Nell Campbell, SoGES 2014-2015 Sustainability Leadership Fellow, and PhD Candidate in the Graduate Degree Program in Ecology.

News flash: at a global scale we still are not doing a very good job reining in greenhouse gas emissions. This is despite the increasingly well-established linkage between rising atmospheric greenhouse gas concentrations and climate changes that can be harmful to human societies and the environment. This is also despite expanding policy to mitigate climate change through greenhouse gas reductions. The most recent International Panel on Climate Change (IPCC) working report released this past year underscores the lack of success reducing greenhouse gas emissions, with its greater emphasis on risk, vulnerability, and adaptation to impending climate change than previous reports.

Energy use is one of the ugly monsters at the base of this challenge to reduce greenhouse gas emissions. Non-renewable fuel use for energy—e.g. fossil fuels—has been long understood as a main contributor of the greenhouse gas CO2 to the atmosphere. However non-renewable energy use is so vital to economic growth and modern human societies that any changes in its use must confront an overwhelming array of other issues and topics: culture, policy, resource availability, societal development, environmental impacts, ethics—the list can go on.  Can energy use change to reduce greenhouse gas emissions without stifling economic growth? This is a key question driving exploration and development of alternatives to fossil fuel energy.

I could hardly hope to tackle such a question in a single blog post! Instead I would like to take a ‘systems thinking’ tour through the small piece of this domain where I spend most of my time: biofuels. Specifically, biofuels created from agricultural crops, and their sustainability in terms of reducing the greenhouse gas emissions released to the atmosphere when fuel is burned for energy.

I am an ecologist. My research sits somewhere between ecosystem ecology, which studies living organisms in the context of their non-living environment, and biogeochemistry, which—as suggested by breaking down the word—is focused on how biology, geology, and chemistry interact to determine global cycles of material such as carbon, nitrogen, and water. I am also a ‘modeler’, which means my efforts to understand how plants and soils—specifically in areas where bioenergy crops are grown—interact with the global carbon cycle are based almost entirely on running computer simulations. Think- experimenting on virtual ecosystems.

Given my background, it is perhaps not surprising that I see ‘sustainability’ as a concept that demands systems thinking. This comes from its basis on some tough questions. What does it mean to sustain? What is the purpose of sustainability as a goal? At the very least these questions are only given meaning when they are also given dimensions: sustaining what? where? how much? how long? for whom? 

To go just a bit further into systems thinking (bear with me), as an ecosystem ecologist and a modeler I further think that a logical goal of sustainability is to be an ‘emergent property’ of how human and natural systems interact. An emergent property is just a fancy way of saying that “the whole is greater than the sum of its parts”, or that the system is doing something that cannot be predicted from looking at its individual pieces. For example, pumping blood is an emergent property of a heart that cannot be recreated by its individual cells, but only happens when cells are coordinated into a functioning whole. Emergent properties are important to people working with complex systems—from the engineer to the ecosystem ecologist to the social scientist—as they can come as a surprise and cause problems if they are either unaccounted or not noticed. A person might think a forest is healthy if they happen to be looking at the one tree unaffected by disease!

From this perspective, the question of whether or not an item or action is sustainable can only be answered by understanding what is happening with the system as a whole. More specifically on the topic of this post, the question of whether energy use can be sustainable in terms of its greenhouse gas emissions requires understanding the greenhouse gas emission impacts of fuel production systems in its entirety.

Agriculture is an area where systems thinking is natural. Agricultural producers have to consider all components of a productive system (e.g. climate, soils, crop nutrient and water demands) to sustain yields and soil fertility through time. What gets trickier is accounting for less direct drivers of agricultural production—the effect of policy incentives, for example, or the economic impact of changes in global demand for a crop due to widespread crop failure elsewhere. Also of concern is the sustainability of other ecosystem features, such as biodiversity, soil carbon storage, runoff water quality, etc. For crop-based biofuels these types of considerations are made even more important by the fact that agricultural lands also provide food and fiber for growing global populations. Productive lands are themselves a limited natural resource. In this context, can crop-based biofuels be a sustainable, renewable energy source that reduce greenhouse gas emissions from fuel use? As an added challenge, the answer might differ if you are asking society as a whole, versus an individual farmer looking to remain profitable.


Figure 1. The theoretical basis of biofuels as a greenhouse gas reduction strategy. Plants extract carbon from the atmosphere via photosynthesis, fixing that carbon into plant biomass that can then be used for energy (B). Ideally this results in less carbon emitted to the atmosphere than through the extraction and combustion of fossil fuels (A), a carbon source that otherwise would have remained stored for geologically long periods of time. Adapted from a video submission to the 2012 IGERT video and poster competition.

In theory, at least, the answer to this question is ‘yes’ (Figure 1). There is widespread experimentation with crop types, varieties, and production methods supported by collaborations between academics, industry, and government agencies. Researchers are, for example, targeting biofuel crops on ‘marginal lands’ that aren’t as valuable for food production, and producers are learning how to grow new crops like switchgrass and Miscanthus—both highly productive grasses—aiming to grow these crops at large enough scales to support viable bioenergy industry. The question that still remains is whether the theory can be realized in practice when these crops are grown at industrial scales. Unfortunately, at the moment there the answer is much weaker (‘maybe’, and ‘it depends’, see the video linked above).

Given the push for solutions to the unsustainable use of non-renewable fuels, the need for greater certainty in these answers is strong and immediate from both governments and industry. Therefore my final piece of the ‘systems thinking’ tour to crop-based bioenergy is to introduce the one set of research methods specifically geared in this direction: life cycle assessment.

Life cycle assessment (LCA) methods are devoted to putting numbers to entire production systems. When I say ‘production system’, I mean everything involved in creating, transporting, and using a product like the fuel that runs a vehicle. LCAs are sometimes more figuratively referred to as an analysis from ‘cradle-to-grave’ (general), from ‘well-to-wheel’ (oil-based fuels), or from ‘field-to-wheel’ (crop-based biofuels). Figure 1 is a good visualization of the bread and butter of fuel LCAs, showing a simplified version of the supply chain that connects raw material (crude oil in A, crop harvest in B) to the final product (the same in both cases: vehicle fuel). LCA methods can put a single number on a gallon of fuel from different sources—say, oil, sunflower seed, and sugarcane—that expresses all greenhouse gas emissions released during the entire process of creating that gallon. Of course LCAs are always open to critique—many assumptions have to be made to put a number on something so complex, depending on data availability, and current understanding of direct and indirect impacts of the production system. This is the basis of standardization in LCA frameworks and approaches. However LCA results are powerful in their simplicity, particularly for evaluating, comparing, and especially communicating the full system impacts of different products and processes. In the case of biofuels, LCAs are a key component of evaluating the sustainability of different production practices, ultimately helping identify ones with the greatest potential to serve as a viable alternative to fossil fuels.

It is unclear, as yet, whether crop-based bioenergy can lead to large-scale reductions in the greenhouse gas emissions from fuel use. However there is clearly potential for crop-based bioenergy systems to offer part of a sustainable energy solution. Doing so just requires keeping a systems perspective…and having a few good life cycle assessment researchers on the team.



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