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 or “sustainable” clothing. 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”. 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).
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. 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.
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.
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, a non-profit organization, is striving to make sustainability reporting a standard industry practice. The International Standards Organization 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 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 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.