In my hour and a half lesson, I was determined to get across one concept: ecological footprint analysis. Pioneered by Mathis Wackernagel and his then-thesis advisor William Rees (see Our Ecological Footprint, 1996), the concept is simple: First, take stock of your lifestyle – the foods you eat, the miles you drive, the amount of waste you recycle. Then, tally up the amount of land it takes to support that lifestyle (a tedious process by hand, but which you can shortcut by using an online footprint calculator, like the one at The Global Footprint Network). Finally, be shocked by the results.
Back in the classroom, we started by figuring out how much land each person on the Earth is entitled to, if all things are equal. (Before you roll your eyes, remember that these were MIT Engineering summer school students, and yes, they really would rather calculate the surface area of a sphere than throw more chalk.) It turns out, if you assume the Earth is 30% land, and round the population to 6.8 billion, that each one of us should be squatting on 21,000 square meters.
Sound big? My students thought so.
In reality, though, that’s only about five acres, or four football fields. (Insert student drawing of four NFL fields, complete with endzones, goalposts, and New England Patriots logos, here. Ugh. I’m a Philly fan.)
How do we fill up those football fields?
“First, we need a place to live,” I said.
“I want my house to fill all four fields!” shouted the tall one in the back. Fortunately, his peers got him to take a knee, and we only brought the house out to the 20-yard-line.
Then, it was time for food. Well, if we got all 2,000 of our daily calories from corn, we’d need 6 bushels a year, which can grow on only 1/25 of an acre. If we account for crop rotation – for sustainable yields of corn, agronomists recommend a ten-year cycle to adequately rest the land – we need to allot about a third of a football field to farmland. Adding some meat (enough for a tenth of a cow, or about 100 meals a year) tags on another half acre.
We looked like we were sitting pretty, with only one football field down, until we remembered that we needed clothes (cotton farms), newspapers and books for school (forests), and maybe some PopTarts for breakfast when we just couldn't stomach another meal of cornbread and hamburgers.
The extra cropland and forestry acreage set us back about 5 acres, if managed sustainably (that means rotating crops to maintain the soil, and cutting trees no faster than they can regrow). We were already exceeding the boundaries of our endzones, and we hadn’t even accounted for the PopTarts!
Those sugary wonders don’t grow on trees, so we need to go to the supermarket to get them, and while there, we should pick up a few other things…
Obviously, we’d forgotten about cars, and the gasoline to drive them. And a TV to watch the football game on the field next door (because there’s no room to play on our plot of land), electricity for the flatscreen and other things around the house, and maybe a plane ticket or two to go visit Grandma in Florida. Wow, that’s a lot of fossil fuel. And there’s more: It took fossil fuel to bring the berries and the flour and the artificial flavoring to the PopTart factory. It took fossil fuel to make the silvery packaging, and it took fossil fuel to ship the breakfast treats to the local grocer. My students quickly grasped the moral: There are hidden carbon costs in almost everything we do.
To be truly sustainable, we have to account for every molecule of the 20 metric tonnes of carbon dioxide the average American releases annually by setting aside land for its reabsorption. Even if we use a generous estimate of 0.75 tonnes of CO2 per acre, we tally up a whopping 21 additional football fields.
Suddenly, our ecological footprints had ballooned to more than 5 times our 5-acre limit. My rowdy, chalk-throwing class got very quiet when we calculated that it would take up to six planet Earths for everyone to live the way we Americans live today. And, because we currently use fossil fuels as an unsustainable global subsidy, humanity is already living as though it has 1.3 Earths at its disposal.
But it’s not my job to depress the young – especially not the ones we’re counting on to get us out of this ever-darkening morass.
One reason ecological footprints make such great teaching tools is that they show you not just how bad the problem is, but also obvious ways to reduce it.
We can shrink our ecological footprints considerably just by changing everyday choices. Since it takes roughly ten times the amount of energy (and therefore, land) to produce 100 calories of meat as 100 calories of vegetables, we can cut our cow dinners in half and eat more vegetarian meals. We can shut down our computers at night, and buy local, organic food that didn’t burn through a barrel of oil during production and transport.
We can also make bigger lifestyle changes, like living in cities, where we can bike to work, use public transportation, and compact suburban sprawl into a fraction of the land area.
Of course, some lace-tightening measures will be more painful than others. For example, the House’s hard-won Waxman-Markey Bill calls for an 80% reduction of greenhouse gas emissions by 2050. Although the bill won’t slow our drain on the planet’s fossil fuel reserves (though it saves the US some political face; see “Lead, follow, or get in the way” for my fairly controversial justification), it provides a useful benchmark. An 80% reduction from 1995 levels would put our per capita emissions at 3.8 tonnes of CO2 per year. For lifestyle comparison, that’s about what citizens of Chile, North Korea, and Syria emit today.
However, we exact a heavy tax on our planet, our fellow citizens, and future generations when we live beyond our means, as we Americans have for decades now. If our footprint calculations are any indication, a serious accounting problem confronts us. The National Park Service may have politely asked us to leave only footprints, but our planet will have the final say on the total number and their size. To leave the place as you found it, you’ve first got to stay on the trail.
Last month, my students left class with a half-dozen ideas to do just that, and about a thousand more brewing in the backs of their minds. Why not put your own mind to the test, and enact some footprint-reducing changes yourself. Tonight. Our planet (and her half-dozen illusory footprint sisters) are waiting.