Watch how you step: A Case for Understanding the Impacts
of Your Personal Consumption on the Environment

By ######


Case Synopsis

With the birth of the 6 billionth living human in October, 1999, the debate about how many people the earth can support before exhausting the supply of natural resources and a clean environment has recently been rejuvinated.  Most current estimates project a human carrying capacity, or the number of people that the Earth can support, at around 12 billion, occurring sometime within the next century. To the extent that material consumption drives energy use, resource extraction, pollution, climate change, and landfill buildup, this means that industrialized nations, although perhaps not more populous than developing nations, have a larger per-capita impact on the environment.  The United States, by virtue of its massive per-capita consumption of natural resources and energy and its generation of CO2 and waste, could be considered the most overpopulated country in the world in terms of environmental impact. Instead of the difficult task of estimating the human carrying capacity (number of people per total land area of Earth), Mathis Wackernagel and colleagues at Redefining Progress developed the "ecological footprint" to quantify humanity's long-term impact on the global environment. The ecological footprint represents the inverse of carrying capacity because it quantifies the amount of land area that is required to sustain the lifestyle of a population of any size--an individual, household, community, city, country, or world. For example, consider the ecological footprint of one human: Given Earth's 8.9 billion hectares of productive land and its 6 billion human inhabitants, the average ecological footprint should be about 1.5 hectares per person if we assume that land use should be equitably distributed among all of the planet's citicens. This per-capita footprint provides an unambiguous benchmark with which to assess the long-term sustainability of population growth and material consumption.  Individual footprints below 1.5 hectares are sustainable whereas footprints above 1.5 hectares are not. In this case, students have the opportunity to calculate their ecological footprint based on personal consumption of resources.  Each student will be able to judge whether his/her lifestyle is sustainable relative to the global benchmark of 1.5 hectares per person and to see what specific consumption categories require the most land to support each year.

Learning Objectives

Upon completion of this case study, students will be able to examine

Intended Student Audience

This case has been written for my freshman-sophomore-level Global Change Biology course at #################. My course fulfills a science distribution requirement for nonbiology majors, but is taken for elective credit by science majors. A typical class may be composed of students from economics, biology, philosophy, sociology/anthropology, environmental studies, English, political science, studio art, and religion. I do not presuppose a strong background in biology or science. To serve this broad audience, I do not focus on scientific methods as much as I take advantage of student diversity to examine the multidisciplinary nature of environmental problems. This and other cases supplement the information students obtain from the following course readings:

1. Wackernagel and Rees 1996. Our Ecological Footprint. New Society Publishers, Gabriola Island, B.C. (a course text)
2. Nelson, M., et al. 1993. Using a closed ecological system to study Earth's biosphere. Bioscience 43(4): 225-236.
3. Cohen, J.E. and D. Tilman. 1996. Biosphere 2 and Biodiversity: The lessons learned so far. Science 274:1150-1151.

This case would also be appropriate for the following sophomore-to-senior level courses:

This case is useful for everyone, and the ecological footprint spreadsheet should be disseminated widely. I strongly recommend that the instructor also use the case along with the students in the course. Many students enjoy this case so much that they pass it along to family and friends.

Context of Case Within Course Structure

This case is an extended, out-of-class project that can be integrated with course topics on sustainability. It is suitable for a two-week or one-month project

On the first day of class, 48 students are divided into small groups of 3 students each. Over the 10-week quarter, my course material is divided among three learning styles: (1) lecture (20 class periods), (2) case studies (7 cases requiring 7 class periods), and (3) in-class strategy sessions where groups present in-depth statements on practical methods for mitigating global change (3 class periods).

Three broad sections structure this course:

Theme 1: Introduction to ecology: What is "natural"? Historical changes in species and climate
Theme 2: And then along comes humans...
Theme 3: Environmental issues at different scales

I use this case after completing issues at the local level (week 5 of 10)--a section at the beginning-to-middle of the course that includes issues related to land use and urban sprawl, private property rights rights, social and economic valuation of the environment, and sustainability. I use two case studies prior to this case: one on the impacts of sprawl in southern Florida on the Everglades and another on local decisions governing deforestation of the Amazon. The case begins during a class period entitled: "How sustainable are land use and lifestyle decisions?" This lecture has the following outline of topics:

I. What do we mean by sustainability? The big glass dome
II. Analyzing direct effects: I = PAT
III. Analyzing indirect effects: The ecological footprint concept
IV. How difficult is it to live sustainably? The evidence from Biosphere II doesn't look so good.

With this format, I introduce students to common uses of the phrase "sustainability" and challenge them to think about what sustainability really means. For emphasis, I use example environmental mission statements from selected national liberal arts colleges, which all use the terminology of sustainability to describe their goals for campus operation. I then ask them if any of these schools are sustainable and show that they are not by using the "glass dome" analogy of Wackernagel and Rees (1996) and described in this case. Basically, the inhabitants of no city (or college) would be able to survive if a glass dome were placed on top of the city, sealing it off from inputs or exports of energy, water, food, and air from outside and exports of solid and gaseous waste. The question becomes how big does the dome have to be to enable all of the inhabitants to survive by including enough land to grow food and forests to absorb CO2 from fossil fuel emissions? This idea of the "ecological footprint" is a definition of how much land it takes to sustain a human population of any size. Most cities are not sustainable because the ecological footprint of cities is vastly larger than the geographic area in which they lie. For example, the ecological footprint of Vancouver, British Columbia is 19 times that of the city's geographic area.

Starting with this general discussion, I move into an analysis of how we can quantify sustainability in terms of humans impact on the environment. We study an example of carbon emissions from Herendeen (1998, pp. 34-35) to show that the product of population (P), affluence (A), and tecnological impact (T) can lead to direct environmental impact (I). Increasing P, A, or T will lead to greater environmental impact, I.

I then ask if these three direct factors are the only ones contributing to how we impact the environment in our daily lives. I use two examples to show that there are also indirect effects of our consumption (Herendeen 1998): (1) How much energy does it take to drive and maintain your car? (2) How much energy does it take to feed you? I give students 10 minutes to work in groups to list items, and they do a good job in showing that operating a car requires substantially more energy than just gasoline. For example, personal indirect energy use from owning a car includes energy needed to (1) drill, extract, refine, and ship petroleum, (2) operating auto retail dealers and maintenance shops, (3) construct highway infrastructure, (4) run auto insurance insustries, among others. Herendeen shows that this indirect energy use can be up to 63% higher than direct fuel use alone. Our impact on the environment is, therefore, much broader than we imagine because of indirect effects.

I then spend about 5 minutes introducing the ecological footprint idea as a way to measure sustainability using data from Wackernagel and Rees (1996). Using a laptop in the classroom, I open the Excel spreadsheet and walk the students through the footprint spreadsheet, showing them how to enter data and the kinds of consumption categories for which they will be account over a 2-week or 1-month period.


How to Use This Case

This case will require at least two weeks (preferably a month) to complete. It is more of a course project than a concept for any single class period. I usually introduce the case in the last 15 minutes of a lecture on sustainability. I show students the spreadsheet in class, and direct them to the case study website, where they have step-by-step instructions on how to engage the case. Then the students spend two weeks to a month outside of class accounting for all of their consumption in 5 categories:

The website has a table that provides a guide for the specific items and quantities students should monitor over the time span.  Data are entered into the blue cells in the spreadsheet. These are monthly rates of consumption, so if students recorded data for a full month, then they can directly enter their data given the appropriate units. However, if they tallied their consumption for the shorter period of two weeks, then they will need to multiply their data by two before entering it into the spreadsheet. I prefer to have students tally these categories for two weeks, because it takes considerable effort to follow them for a whole month, and students have found this too difficult logistically to handle in a busy schedule. Once students have entered monthly consumption for these items, the footprint spreadsheet converts the amount of goods and services consumed and waste produced into an area of land needed to support a person's lifestyle. 

Ways to teach case

There are three levels of difficulty and engagement that make this case suitable for high school levels up to senior-level undergraduate courses.

1. Simple-- This scenario is appropriate for high school students or college freshmen-level courses. In this scenario, students just plug numbers into the spreadsheet and then examine their ecological footprint size. This is what most online footprint calculators do.

2. Intermediate-- This level is most suited for the majority of introductory and mid-level college courses. Here, students should understand how each of the consumption categories contributes to their footprints. They can trace the numbers in the spreadsheet to learn how the six consumption categories require the use of fossil energy land, arable land, pasture, forest, built-up land, and the sea. This information can be found at the Introduction to calculations link on the case webpage. This is the level that I expect in my 100-level Global Change Biology course.

3. Advanced-- At this level, students should understand the mathematical and theoretical basis of calculations for converting each good or service into land area. This information is detailed and will probably require that the instructor walk through an example calculation with the students. Detailed information on how the spreadsheet calculations work can be found on the case webpage at "Specific Notes about the Spreadsheet Calculations"

For advanced students who want to determine how indirect effects are incorporated into the calculations, the instructor will need to describe the differences between "bottom-up" and "top-down" footprint approaches and how national aggregate data can be used to determine appropriate correction factors. This kind of information can be found on the case webpage at "Other notes about the Spreadsheet Calculations"

What to expect

There are generally few surprises for the instructor as a result of using this spreadsheet. Students with the largest footprints tend to consume more materials and energy, travel more, eat diets rich in meat and other animal products, and recycle little. Students may be surprised at how much land area it takes to support the 6 consumption categories.

I often have students convert the footprint land area into the equivalent number of football fields so that they can visualize this area easily (1 hectare = 100m x 100m = 10,000 m2 = 2 football fields side-by-side).

Footprints should range between 1.5 - 10 hectares, with an average usually around 4-6ha. Footprints larger than 10-15 ha are quite high, so if students have footprints larger than this, instructors might have them double check their calculations for errors.

Follow-up Assignment

Following the case, I usually spend about 15 minutes on the last day of class having students describe their reaction to this analysis, and we talk through the 5 questions for further thought. Many are shocked at how large their footprint is. Most agree that it is very enlightening seeing specific details about their consumption, and many indicate that they are now much more concientious about how much they consume. For fun, I usually award a footprint award certificate to the person with the smallest, most sustainable footprint, which usually is around 1.3 hectares for vegan students living on campus.

The case assignment is a short written report that includes a printout of the spreadsheet and thoughtful discussion of the following five questions:

1.  List the factors that contributed to your footprint, from the largest to smallest contribution, what did you find?  Are you surprised or shocked by these results?

These results vary from student to student, but generally transportation is the largest contributor, especially for students that drive or commute a lot.

2.  Based on your ecological footprint calculation, where might you consider your lifestyle to be sustainable?  Not sustainable?

Answers vary from student to student depending on personal consumption.

3.  What specific actions could you take to reduce your footprint?

Answers vary from student to student depending on personal consumption.

4. How realistic/achievable are these reductions?  Would they force you to live a fundamentally different lifestyle?

Answers vary from student to student depending on personal consumption.

5.  How do you feel about the fact that the average footprint of a citizen in the United States is 4-10 ha compared to the global average of 1.5 ha?  Why is this the case?  Should anything be done about it?  If so, what?

Again, a normative question, but one that forces them to think of the general equity of their consumption with respect to citizens in other parts of the world.

Common Pitfalls Encountered by Students and Instructors

There are a few areas where students often have difficulties.

1. The most difficult category to account is energy use, so I send them an email with information on how to do this. I also have researched power consumption at ####### with the help of staff in ######'s maintenance and facilities unit, and I have data for energy use for whole dorm buildings.

Here is an example email that I send out to class the day we begin the footprint case:

I am attaching an excel spreadsheet file with gas, water, and electricity for the buildings on campus for which these records are kept. I am also putting this file on the course folder. The columns that are starred are the values that you will work with.

A couple of points:

1. Most of your dorms/houses will be on here. Calculating YOUR share of energy use requires that you divide the total energy used by the number of students in the dorm. If your dorm is not listed, please do the best you can estimating your water, electricity and heat use. For water, it's as simple as figuring out how much you use to drink, shower, etc. For electricity, it's how much you use various appliances and lights. Most appliances and lights are rated in watts, so you can figure out how many watts you use per hour. For example, if I use a 100 watt bulb for 20 hours, that amounts to 2000 watt hours or 2 kilowatt hours (Since electricity is about 5 cents per kilowatt hour, I would have used about 10 cents of energy). For water, you can place a 2 liter bottle under faucets or shower and quantify the amount of water flowing over a given time. For example, let's say I placed a bottle under the shower tap for 1 minute and collected 2 liters. If I take 10-minute showers, I know I use 20L of water.

2. The units of housing are square feet; the units of water are gallons; the units of gas are CCF (hundreds of cubic feet); and the units of electricity are kilowatt hours (kwh).

3. The values in the data spreadsheet here are ANNUAL. To enter them in the blue cells on the footprint spreadsheet, you will need to make them MONTHLY values by dividing by 12.

4. Note that the square footage of the dorms are given. You can divide this value by the # of people in the dorm to estimate your contribution to the housing footprint.

5. Estimate how much electricity and water you use in other buildings, such as the Library and CMC. The goal is not rocket-science accuracy; just do the best you can, and have fun estimating these. How many hours do you spend in these buildings? How many lights are in the ceiling of these rooms? How many other people are in the rooms at the same time (use the total # of people to calculate your contribution). For example, let's say I spend 5 hours/day in the Libe. Let's say there are 30 100 Watt bulbs in the room I work in there and that an average of 10 other students work in that room at any given time. My own energy consuption per month from that room would be 30 bulbs * 100 watts/bulb *5 hours/day *30days/month = 450 kilowatt hours/month for all 10 people, or 45 kilowatt hours for me alone. Pretty straightforward. You can do this kind of estimate for electricity in all the rooms you inhabit on campus.

[NOTE TO INSTRUCTORS: Wackernagel and colleagues would recommend eliminating the accounting in step 5, because it may double count electricity that is already captured in the indirect effects corrections. I prefer to have students do step 5 anyway because most students live more in the library than then do in their dorm, and it gives them practice with explicitly accounting for personal energy consumption.]

6. For food, do the best job you can in estimating weight. If you live off campus and don't use a meal plan, the weight of the food will be on the packages, or you could use a small scale. If you eat on a meal plan, you can estimate the weight of each food item.

2. Students should not enter the cost of their tuition in the education component of the services category (doing so will lead to an astronomical footprint size). This category is intended for educational services, like paying for someone to make photocopies.

3. This third issue is rare, but very important to consider. Some students have eating disorders, and they have been advised by their physicians and psychologists to not account their food in any way. Make the general point known to students that if they are unable to keep track of any of the 6 categories to come talk to you. For the one student that had an eating disorder, I recommend that this person should skip the food category but to keep track of consumption in other categories.