∫ Taking Sustainability to Quantitative Heights

The word ‘sustainability’ triggers a range of buzzwords: responsibility, environmentally friendly, safe, organic, equitable, recyclable, long-lasting, renewable, profitable, or biodegradable. As consumers, we now have the option of purchasing ‘sustainable’ seafood[1] or “sustainable” clothing[2]. Most famously, in 1987 the Brundtland Commission defined sustainable development as “meeting the needs of the present without compromising the ability of future generations to meet their own needs”[3]. There may never be broad consensus for an appropriate description, but generally ‘sustainability’ has increasingly involved thinking holistically about a certain product or service. And in recent years, we have begun to build the analytical framework to quantify the meaning of ‘sustainability’, better known as Life Cycle Assessment (LCA).

Figure 1: Whole Foods market outreach to promote sustainable seafood choices. (4)

We will explain the general Life Cycle Assessment theory now, and then use a simplified LCA to quantitatively compare the true benefits and costs of incandescent versus compact fluorescent (CFL) bulbs. There is a three step process to a Life Cycle Assessment. First, researchers outline the goal and scope of the assessment. This tailors the system boundaries and centralizes the analysis around a specific sector or product. For example; do we care only about the direct emissions from our building, or are we interested in the emissions behind the meter? Second, researchers use one of several quantitative methods to build an inventory of the inputs and outputs for a given product system throughout its entire life cycle or supply chain, capturing the total material, emission, and energy flows within the system boundaries. Third, researchers conduct an impact assessment based on the inventory analysis. These impacts broadly fall into categories such as ozone depletion, human toxicity, or global climate change. Taken together, a thorough LCA provides the quantitative measures to draw conclusions and iterate a service or product.

Generally, there are two methods to conduct a life cycle assessment. An Economic Input-Output (EIO-LCA) approach quantifies the material, energy, and financial flows resulting from economic activities within different sectors. This was developed principally by Wassily Leontif in the 1970’s and brought into mainstream use by Carnegie Melon University[5]. A Conventional (or Process-Based) Life Cycle Assessment approach focuses on a specific product or service rather than a sector, typically defined by a function and normalized with a functional unit. For example, the purpose of a PV plant is to supply electricity (function), and the basis for the LCA could be a kWh of electricity (functional unit). The major advantage of this method is the ability to differentiate two products or services that have the same function.

To put this theory to practice, let’s consider the decision to replace a light bulb with either a CFL or incandescent bulb using a Process-Based LCA. Since we’re concerned about both our pocketbook and the environment, let’s use our LCA to quantify both the financial aspect and two emission streams (mercury and CO2 emissions), and limit the scope to lighting and disposal.

Using a simple LCA to determine the most 'sustainble' lighting choice (6).

The function of the light bulb is to provide lighting for 6 years (6 hours / day), with a required functional unit of approximately 700 lumens of lighting (fairly standard bulb). A quick Home Depot search turns up two bulbs capable of providing the necessary illumination: an incandescent bulb ($1.30, 60W, 986 hr lifetime) and a CFL bulb ($6.50, 13W, 9855 hr lifetime). A deeper look reveals that the CFL has up to 0.03% mercury content, a concern amongst some homeowners. At first glance, it may be enticing to go with the incandescent; the low cost and lack of mercury may seem like an easy decision. But let’s expand the analysis.

The six year lighting scope translates to 13,140 hours of illumination. This means we need to purchase 2 CFL’s and 14 incandescent bulbs, based on our manufacturer lifetime guarantees. When we account for the electricity consumption, this translates to ~171 kWh for the CFL, and ~788 kWh for the Incandescent. Using a price of $0.12/kWh for electricity, this becomes ~$20.50 for the CFL and ~$94.60 for thei. Suddenly the financial picture shifts; the total cost for the CFL bulb becomes ~$33.50, and the Incandescent bulb ~$113.30, a difference of nearly $80 in favor of the CFL.

The environmental picture is a bit more complicated. The US grid emits ~0.012 mg of mercury and 0.66 kg of CO2 per kWh of electricity. If we assume all of the mercury already in the bulb ends up in the landfill, the CFL releases a total of 9.2 mg of mercury and 113 kg of CO2. The incandescent bulb releases 9.4 mg of mercury and 520 kg of CO2. Essentially, the increased energy consumption penalizes the incandescent’s CO2 emissions inventory.

Life cycle inventory of cost, mercury, and CO2 emissions.

This simple Life Cycle Assessment exercise highlights the importance of thinking holistically, giving us the measurements to make a ‘sustainable’ choice. From a financial perspective, the CFL is the clear winner. From an ecological perspective, the CFL has a much better CO2 emissions profile, and both bulbs perform equally with respect to mercury emissions.

Today, various organizations have begun to promote sustainability through more rigorous quantitative frameworks. The Global Reporting Initiative[7], a non-profit organization, is striving to make sustainability reporting a standard industry practice. The International Standards Organization[8] currently has voluntary Life Cycle Assessment standards as part of its 14000 Environmental Management Series, with the intention to indentify, improve, and monitor the environmental impact of activities. The Earth Day Network[9] provides a simple tool to calculate the ecological footprint of a lifestyle, using earth’s global hectares instead of materials or dollar indicators. High end LCA software such as SimaPro[10] gives the ability to create very detailed inventories for unique systems.

Some products that claim to deliver energy efficiency are actually just energy reductions without the efficiency. Doing the same thing more efficiently does not sacrifice an end product (light levels stay the same, the amount of cooling your AC provides remains the same, etc.), energy reductions not gained through energy efficiency might sacrifice operations or comfort. Energy reductions are fine where appropriate – many commercial office spaces in the U.S. have lighting levels well in excess of modern recommended amounts and are therefore excellent candidates for removing 10-40% of the lamps – but if light levels are already appropriate, reducing the number of lightbulbs may not be a good idea.

Fundamentally, life cycle assessments attempt to measure sustainability to aid decision making. Much work remains to standardize the framework and better interpret the impact assessment, but it’s exciting that Life Cycle Assessment application has moved into mainstream discussions. In the meantime, give your personal life an ecological score with Earth Day’s nifty calculator found here.

[1] http://www.wholefoodsmarket.com/values/seafood.php
[2] http://www.amourvert.com/green/
[3] http://www.un.org/documents/ga/res/42/ares42-187.htm
[4] http://www.wholefoodsmarket.com/seafood-ratings/
[5] http://www.eiolca.net/
[6] sophia.smith.edu
[7] https://www.globalreporting.org
[8] http://www.iso.org/iso/iso_14000_essentials
[9] http://www.earthday.org/footprint-calculator
[10] http://www.simapro.co.uk/

19 Responses to ∫ Taking Sustainability to Quantitative Heights

  1. Awesome article! I think you’re right on in looking at the cost and overall impact of a product from a holistic view vs. just looking at face value. I’ve had to re-train myself to take this approach over the past few years, but I definitely think it’s worth spending a little time doing.

    Additionally, great point about comparing energy ‘reductions’ vs. energy ‘efficiency’! I think a lot of people see these as synonymous, but good to outline the difference.

  2. Haley,

    I think you make an excellent point about reductions vs efficiency. Simply because a motor, lamp, or HVAC system is running “efficiently” does not necessarily mean it is the most cost effective or environmentally friendly approach. Sometimes it requires stepping back and analyzing the entire picture.

    Thanks for reading!

  3. Thanks for explaining the light bulb debate! Looking forward to more articles that can clarify the numerous contradicting articles on these subjects!

  4. TWG,

    This is just one example of how thinking holistically can reveal hidden benefits or tell a more accurate story.

    Thanks for checking out the blog.

  5. Great article. Your light bulb comparison provides a good example of how the economics of an item goes beyond the cost at the store. There are both economic and environmental costs of the energy used. Society needs to think beyond the price tag and recognize the long term costs associated with a purchase.

    • Excellent points WN. With a simple LCA approach, it doesn’t even need to be a ‘society’ decision. It can simply be a personal decision to save money or improve the local environment.

  6. So what if we include the probability that I drop and break my CFL light bulb in an absorbent part of my house multiplied by the cost to have an approved contractor clean it up? Probably outside of the boundaries of my LCA, eh?

    But then again, how many mg of mercury are in a can of tuna?

    Heard some mixed stories on this. Matt, can you clarify?

  7. This article is really interesting. It is well written, well explained, and overall, provides a global vision about what sustainability means. What I liked more is that through an everyday example give you a holistic vision of a complex concept: efficiency Vs. reductions. Another important idea expressed in this article is the real ecological cost of a product that is beyond of the superficial information that the people know.
    Finally, I would like to point out that, as you probably know, some European governments are trying to introduce low consumption light bulbs via subventions, to reduce the high purchase price of the product. This article would be very useful for educational purposes.

    • THI,

      You bring up a good point – it’s often difficult to internalize the ecological cost of a product purely with the label. It usually takes some effort to quantify the impact, and an LCA is a solid approach to do so.

      Thanks for pointing out Europe’s attempts to influence the purchasing of low-consumption light bulbs. To me, this seems like a reasonable attempt to represent the holistic cost of the product upfront.

      Thanks for reading!

  8. An illuminating article, ah-HAHAHAHAHA! Thanks for putting numbers to the debate.

    I bet if you changed the title a bit to be more descriptive of the topic of CFL vs Incandescent you may get more readers…

  9. On the pure CFL vs. incandescent debate (which is not necessarily the point of your article), it would be interesting to add in the third option of LEDs.

    In general I think you have a good point, that quantitively analysing the options can improve the choices we make, but I’m not sure that without regulation forcing companies to add this info to their product packaging or adverts this can be done in a way that will really aid consumers to make the best choices. Most companies main goal is profit and to sell their product, and as a result they will highlight the plus points from this analysis, and go easy on the cons. For example, though one company might happily quote numbers that are positive to its product, they would likely ignore the negative aspects and vice versa for a different producer. So when you go to the grocery store looking for bulbs, whose word do you trust?

  10. Tom,

    Your comments are well said. I don’t think there is enough agreement yet about the framework of LCA’s to implement formal regulations, but several voluntary standards from well-known entities such as the ISO (http://www.iso.org/iso/iso_14000_essentials) have helped move the discussion towards that goal. Imagine being able to read the LCA carbon or PM10 level right next to calories on a box of cereal.

    Thanks for your comments, and keep on reading!

  11. Thanks for the article! I was pleasantly surprised to see that you take human toxicity from mercury into consideration, since it’s difficult to quantify its effect on human health or the environment, but is still important. I always just thought of CO2. I would be interested to see a different and possibly more complex example of LCA with a less-clear winner to see where some of the tough decisions are made.

    Also, this method is very dependent on the goal that you set. In your example, you picked lighting a space for 6 years. If the choice were lighting a space for 1 year, you may have come up with the incandescent bulb — better for the company paying for the lighting, but not better for the environment. I think this touches on the point that Tom makes about needing regulations, since the nation as a whole might be the only party with a large enough scope to really make decisions that will impact the environment.

  12. Martha,

    Thanks for reading! You bring up some excellent points. Life Cycle Assessments are particularly good at tracking material, pollutants, or energy, but making the connection to human health or environmental impact is one of the next frontiers in this area of research.

    Another challenge with Life Cycle Assessments involves establishing the boundaries of the study. You’re right – using 1 year or 10 years will likely result in different impacts or costs. The IPCC has a similar issue with quantifying the impacts of climate change. This is why it is appropriate to run sensitivities and capture a range of outcomes.

    I disagree that the ‘nation as a whole’ will be the best/only clearinghouse for LCA decision making. Large corporations and companies progressively use forms of LCA’s for long term strategy. For example, life cycle costs have become the de facto method to price projects via a Net Present Value calculation. Additionally, companies today need to think about how EPA air regulations impact their long term strategies.

    Thanks for reading!


  13. This is a very interesting article and I like the comments been left with regards to his article. One point I want to make is that while these initiatives are great, we must remember than often education is a the key difference. Coming from a third world country myself, I do not think of the difference between the emissions between the two bulbs, but more along the lines of what will cost me less over the course of the bulb. Perhaps we can account for the geographic and economic factors when performing this LCA analysis.

  14. Great article! Working on the homeowner relations/education side for a solar contractor, we definitely try to push energy efficiency and conservation measures in conjunction with solar power so our homeowners can maximize the benefits from their pv systems. Analyses like these help to make my job easier, so I have facts and figure to use when talking with homeowners.

    Just as something else to consider, change based on these ideas and numbers can also come from policy and legistlative level. In this case, California is removing higher cost options at the point of manufacturing:

    Not to say we need can solely rely on policy everytime we want change, articles and analyses like these help to educate at the point of consumption. I think when used in combination with policy, truly integrated mangement of our energy consumption is possible.


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