There are advantages to being a writer named Wackernagel, and chief among these must be shear memorability. Some years ago, when I was explaining the concept of ecological footprints to my then-boyfriend (now, husband), he, in frustration, demanded to know where I'd gotten this stuff.
"Mathis Wackernagel!" I retorted, proudly.
This sort of thing is very encouraging for writers with strange names. If mine ever comes up in an argument with your mate, it's easier to pronounce than it looks; A lan thus. The "i" doesn't do much, so you can ignore it.
Anyway, the idea of the ecological footprint starts with the fact that a certain portion of the Earth's surface is dedicated towards your personal upkeep. Imagine that you are a subsistence farmer, and that all the water you use falls as rain on your farm, all your fuel wood comes from your farm, all your waste is composted there, and so forth. In such a scenario, your ecological footprint is the area of your farm. If you start buying hay from your neighbor, then your ecological footprint, or EF, grows to include part of your neighbor's hay field. If you sell produce to raise money with which to buy hay, then part of your vegetable garden is transferred to the EF of whoever buys your produce, and tracing the location of your EF very quickly becomes impossibly complicated. It is still possible to calculate the rough size of your EF, however, if you know how much land is necessary to support all the things you do. For example, If you eat a loaf of wheat bread every week, you can calculate the size of the wheat field necessary to make your bread, because you can find out the average yield per acre of wheat.
The reason ecological footprints matter is that there is a finite surface area of the Earth. The total surface area of the Earth is the maximum total ecological footprint. Dividing the Earth's total surface area by the total human population yields the "fair Earthshare," or the size that everyone's EF would be if resources were distributed equally. If your EF is bigger than a fair Earthshare, then either someone else is using less, to subsidize you, or you are borrowing against the future by using resources too fast. It has nothing to do with how much you deserve, how good a person you are, or how much you care about the planet, it's just a measure of how much you use in comparison to how much there is. It's just math. Ecological footprint calculation is a way to make ecology personal.
This book is an introduction to the concept, and also a detailed description of how to calculate your own footprint. You can also get a rough estimate of your footprint through any number of online EF calculators, though the online calculators simplify the calculation by making a lot of assumptions, which may not be relevant in your case. Reading this book will give you the context to understand that calculators better. Ecological footprint is different from carbon footprint, by the way; your ecological footprint includes your carbon footprint in that one of the things you need Earth's surface area to do is to re-sequester the carbon emissions freed by your lifestyle. EF distills your entire ecological impact to a single measure; surface area.
The book's descriptions are clear, and the pictures are thought-provoking and funny. The authors explore a number of different implications of the EF concept, far more than I have space to summarize here. If the authors have a weakness, it is their tendency to announce periodically that EF calculations are fun! which they aren't, but at least the whole thing is important food for thought.
And no, ecological footprint calculations are not as simple as the online calculators, or even this book, make it seem. For example, the carrying capacity of an acre quite obviously varies, not only across space but across time. A degraded ecosystem can't support as many people as it once could. A related complication (and one the book does address, at least in part) is that resource use is rarely about absolute amounts. Sustainable resource use is a matter of rate. It's a bit like finance, to use a metaphor Wackernagel and colleagues also use. If you've got $100,000 invested and earning 1% interest per year, then you can spend $1000 every year forever. If you spend $2000 a year, you will eventually run out of money. With environmental decisions, the big question is always are you spending the interest or are you spending the principle? Since not all acres on the planet have the same sized endowments, and the size of the endowments changes as the principle is spent, calculating a sustainable rate of use that is valid all over the planet and then expressing that rate as an area is at best an estimation tool.
There are other complications. The ecological footprint is not a tool one can use without a great deal of thought--but that's not really the point.
The point, first and foremost, is that ecological limits may be complex and difficult to understand, but they are not arbitrary or subject to debate. It's like driving a car (and this is my own analogy). If you hit a patch of ice on the highway, what happens next to your car has nothing to do with how much you deserve to have a good day or how important it is for you to get where you're going. What happens to your car is a matter of physics, and physics dosn't care what you think. Environmental issues are equally non-negotiable. There is only so much of the planet to use, and that's all we get.
Secondarily, the concept of the EF gives environmentalism a clearly defined goal, at least in theory. Much of the talk of "green" living these days is entirely relative; you hear about saving so many trees or keeping so many tons of greenhouse gas out of the atmosphere, but there is really no way to put any of this in context. On a bad day, it's possible to conclude that no one can ever be green enough, so why bother? On an entirely different kind of bad day, it's possible to conclude that since you recycle and do other "green things" periodically, you're already doing enough. EFs are the antidote to this kind of relativistic thinking. If your EF is equal to your fare Earthshare or smaller, you're done! You're sustainable! You've arrived! In practice, you might not be able to work through the various complications well enough to define your EF that precisely, but at least that finish line exists, and you can approximate it.
And in the process of finding your way to living within your fare Earthshare, you'll probably make it easier for the people around you to find their way there, too.
Reese, W.E., Wackernagel, M., Testemale, P. (1998). Our ecological footprint, by Reese and Wackernagel. New Society Publishers.