Life Cycle Assessment

Fossil fuels seemed so simple at the dawn of the energy age: Dig a hole, extract the oil or coal, transport it, process it and burn it.

In the second half of the 20th century, however, it became clear that fossil fuels would not last forever. At the same time, scientists raised concerns that oil and coal emissions were harming the environment, leading to increased scrutiny of everything from automobile tailpipes to power plants.

At a time of rapid climate change, rising energy prices, and the urgent problem of greenhouse gas emissions, fuels demand more investigation than ever before. To that end, scientists are engaging in increasingly complex versions of Life-Cycle Assessment, cradle-to-grave evaluations of products and technologies.

The life-cycle approach can assess a host of energy options, including biofuels. A full Life-Cycle Assessment, or LCA, can help quantify the economic and environmental costs of biofuel sources. So what, exactly, is an LCA, and how do you use it?

No Easy Answers

Put simply, LCAs evaluate the impact of technologies and products to answer key questions: How many resources are consumed, how much pollution is generated, and who or what is harmed by the pollution?

This involves following the manufacturing process from extraction to waste disposal. One of the earliest life-cycle assessments looked at the environmental cost for Coca-Cola to switch from glass to aluminum cans. Another early LCA compared the environmental toll of paper and plastic cups.

LCA can never be the only way to assess an environmental footprint, of course, because its comprehensive approach requires tackling uncertainty. In addition, the answers delivered by an LCA depend on the questions asked.

The approach, in short, is more of a philosophy than a set of formulas. What LCAs do encourage is informed decision-making. In recent years, LCAs have assumed a key role in government energy policies, including the national Renewable Fuel Standard, which mandates that 36 billion gallons of biofuels be blended into transportation fuel by 2022.

The Energy Independence and Security Act of 2007, for example, requires that the Environmental Protection Agency assess life-cycle greenhouse gas performance thresholds to make sure that each category of renewable fuel creates fewer greenhouse gases than the petroleum fuel it’s replacing. The current challenges include finding more sophisticated ways to mine data, identifying as many pieces of the puzzle as possible, and devising better ways to put the pieces together.

LCA Basics
Before beginning an LCA, researchers define the goals and scope of the project. They then collect many types of data, measuring both inputs and outputs. In evaluating fuel production, inputs include:

  • raw materials, such as minerals or ores
  • energy sources, such as electricity and petroleum
  • water withdrawals and consumption

On the other side are the outputs, including:

  • greenhouse gas emissions
  • toxic pollutants
  • hazardous and nonhazardous waste

How you divide the input or output flows in a life-cycle assessment can have an enormous impact on its outcome. In a study on rapeseed-to-bioelectricity production, researchers in the Netherlands found that one method predicted a 16 percent impact on greenhouse gas emissions, while another estimated a 60 percent change.

After researchers collect the data, they analyze impacts on the environment throughout the product or technology’s life cycle. The last step is interpreting the findings so they can be used to guide decisions.

  1. 01. Understanding farms, feedstock options and land use: Biofuels begin with feedstocks. Current feedstocks such as corn and sugarcane are farm grown, and future feedstocks may come from farms, rangelands or forests. All of these sources could have consequences for the cost of food, forage or fiber. One issue is potential deforestation, which could exacerbate global climate change. To complicate things further, the first stages of production are likely to involve hundreds to thousands of decision-makers, including farmers and ranchers.
  2. 02. Predicting biofuel production technologies and practices: There are lots of alternatives for making biofuel, and these processes are constantly evolving. Every innovation adds potential uncertainty to an LCA. How much electricity will new facilities use? Will facilities deliver a single fuel product, or will they have multiple product streams? What are their waste products, air emissions and water demands?
  3. 03. Measuring tailpipe emissions and their health consequences: Transportation is a major causes of urban air pollution, and scientists will need to get an accurate measurement of  the emissions from vehicles running on biofuels in the future. But this is a challenge for LCAs, because few studies of tailpipe emissions have examined more than a handful of air pollutants. When researchers have evaluated the health damage from air pollution, they tend to emphasize the risk of premature death rather than the overall disease burden.
  4. 04. Accounting for location differences in data collection and assessments: The exposure and health risks of pollutants can vary by orders of magnitude depending on where they are emitted. The interwoven highways of a big city, for instance, are very efficient at delivering pollutants to a large population compared to the impact of a rural road in an unpopulated area. Geography also influences soil carbon impacts and water demand
  5. 05. Accounting for “moving targets” that change over time: Many important details of biofuel production are constantly in flux, including population distributions, vehicle fleet composition, technology options, regulatory requirements and the degree of biofuel penetration in the overall energy mix; Greenhouse gas emissions that can influence climate change are moving targets, too, although climate change moves on the scale of decades or even centuries. Pollutants emitted by tailpipes and production facilities accrue within years and are taken into account in most LCAs, but greenhouse gas emissions are often discounted because of the slow pace of climate change. This discounting can strongly influence the outcome of LCAs, yet there is no clear rationale for such decisions.
  6. 06. Evaluating transitions and “end states” as technology matures: Currently, LCAs often focus on system “end states” – what biofuel production and use will be like 20 or 30 years in the future. This ignores potentially important effects during the transition phase when new infrastructure, new vehicles, and so on, are being built. In addressing transitions, there should be recognition that emerging technologies could change the assumptions underlying biofuel LCAs. Changes in consumption patterns or in urban land-use policies, for instance, could open substantial land for biofuel production.
  7. 07. Confronting uncertainty: This is among the greatest of the LCA challenges, and not only for biofuels. When facing uncertainty and variability, it’s important to stay realistic. A good LCA can provide the data needed to make the right decisions. It’s especially important to have clear metrics showing how the information was acquired, whether the data have been corroborated, and how well the data capture variations in technology, location, and time.

Uncovering Hidden Health Impacts

A good LCA goes beyond the surface to get at the whole picture. No analysis can be entirely complete, but the challenge is to find the best and most accurate data — while allowing for some uncertainty — to arrive at the most defensible decisions.

Take the example of hydrogen-cell fuel buses, which are often billed as “Zero Emissions.” But are they? In terms of tailpipe emissions, this should be true, because water vapor is the only product of hydrogen combustion – i.e., it’s all that is being released.  But the in-depth approach of an LCA takes into account the supportive infrastructure required to maintain the buses, which might include pipelines, truck transport, fueling stations and hydrogen generation plants and their associated emissions.

LCAs can also uncover hidden health impacts, including those caused by the inevitable pollution that comes with transporting fuels over large distances. In theory, driving a truckload of ethanol from Des Moines, Iowa, to Newark, N.J. (about 1,100 miles) should produce about as many emissions as delivering an identical load from Sioux Falls, N.D., to Long Beach, Calif. (about 1,300 miles). But a thorough LCA shows that distance traveled is not a good proxy for health impacts. The East Coast route travels through a much more densely populated area and therefore will pose a bigger threat to human health.


How can an LCA be designed to address a specific problem?
Make sure it addresses these basic questions: How serious is the problem? What will it cost to fix it? Is that the best way to use the money available?

What’s the best way to use LCA, and what pitfalls need to be avoided?
The best analyses start with specific questions tailored to the subject at hand. A broad-based question like, “What is the environmental impact of biofuel,” gives rise to a host of sub-queries and won’t yield good results. Equally problematic is trying to use an LCA as a “gatekeeper” to give the green or red light to proposed projects. The best use of LCA is to achieve an understanding of the whole process while minimizing harmful impacts.  

What are some of the shortcomings of an LCA?
Almost every problem needs a unique LCA solution; there’s no “one size fits all” model. Data availability and reliability are a challenge, and defining problem boundaries for LCA —  how far the study should go in looking at possible consequences  — is controversial. An LCA can take too long to be useful for an initial design process. It can be difficult to take the dynamics of changing markets and technologies into account. Finally, interpretation of LCA results varies from one stakeholder to the next.

What are the biggest issues when assessing the impacts of fuel?
Carbon emission, water use and human health are the Big Three of energy impacts. It’s important to assess those impacts in a local setting. Scientists developing a biofuels LCA model at the Energy Biosciences Institute are taking a county-by-county approach as they try to figure out the exact location of production, refining and use.

LCA Tools Online

Several Life-Cycle Assessment tools are available free online, including:

The Economic Input-Output Life-cycle Assessment
Carnegie Mellon University
This website has transformed LCA by merging input-output economics formalized by Nobel Prize-winning economist Wassily Leontief and publicly available U.S. environmental data into a user-friendly tool to evaluate a commodity or service and its supply chain. Free for non-commercial use.

GREET online
Argonne National Laboratory
To evaluate advanced vehicle technologies and new transportation fuels, researchers have to look at the fuel cycle from wells to wheels. Sponsored by the U.S. Department of Energy, Argonne has developed a full life-cycle model called GREET (Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation). Free of charge for anyone to use.


Elementary flow: 1. Material or energy entering the system being studied, which has been drawn from the environment without previous human transformation.  2. Material or energy entering the system being studied, which is discarded into the environment without subsequent human transformation.

Input:  Material or energy which enters a unit process. Materials may include raw materials and products.

Output:  Material or energy which leaves a process. Materials may include raw materials, intermediate products, products, emissions and waste.

Raw material: Primary or secondary material that is used to produce a product.

Unit process: The smallest portion of a product system for which data are collected when performing a Life-Cycle Assessment. Unit processes have a series of associated inputs and outputs.

Waste: Any output from the product system which is disposed of.


Credits: This Briefing report was created by Michelle Locke and Chris Woolston in collaboration with EBI researchers Thomas McKone, an adjunct professor in the School of Public Health at the University of California, Berkeley, and Arpad Horvath, a professor in UCB’s Civil and Environmental Engineering department.



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