"We all know that stealing means we are not to take things that do not belong to us — no shoplifting, pick-pocketing, or armed robbery. However, there are other, more subtle ways to steal. Ever since the prophet Jeremiah brought the word of the Lord to those who had grown 'great and rich . . . fat and sleek' (Jer. 5:27-28), at the expense of others, there has been a broader interpretation of the eighth commandment. It is summed up in one word: justice.

"It is unlikely that most of us have stolen recently in the first, narrow sense of the word: actually filching somebody else's belongings. But the sad truth is that probably every reader who lives in a First World country, myself included, is actually a thief.

"I discovered my culpability during a lecture about one of the tools that environmentalists use to weigh justice. It is called an 'ecological footprint.' According to Mathis Wackernagel and William Rees, an ecological footprint is 'an accounting tool that enables us to estimate the resource consumption and waste assimilation requirements of a defined human population or economy in terms of a corresponding productive land area.' In short, how many acres — fishing grounds, forests, pastures, or agricultural fields — does it take to maintain a given lifestyle?

"The questionnaire that accompanies Wackernagel and Rees's book asks the reader to calculate their household's ecological footprint by recording a month's worth of consumption of food, consumer goods (such as clothes, paper products, and medicine), use of transportation, housing costs, and waste removal. When instructions for this project were distributed in my environmental studies class, the enterprise seemed daunting, and I postponed it.

"I continued to be curious about my own impact, however, so I was relieved when I discovered that there was an abbreviated form on a website: www.MyFootprint.org. It takes only a few minutes to complete, and serves as a very approximate gauge of one person's consumption of earth's resources, unlike the more exhaustive quiz that can be found in conjunction with the Wackernagel-Rees book.

"How virtuous I felt as I began the process of typing in my answers! We live in a modest home heated and cooled by sustainable energy, eat very little meat, and try to buy organic and local food and to use environmentally friendly new technologies whenever we are able. I didn't feel so virtuous when I finished it. After all was said and done, I discovered that my husband and I each need twenty-one acres to sustain our lifestyle, in part because of my frequent plane travel. (Since then, I have discovered that I can buy 'carbon offsets' to neutralize this travel, through investing in a wind farm or forestry project.) According to the World Wildlife Fund's Living Planet Report 2006, which reports 2003 ecological footprints, we do a little bit better than the average U.S. citizen, who uses twenty-four acres per person. But we lag behind the Canadians just to the north, who are able to get by with nineteen acres, or the Italians with only ten. The Pakistanis, on the other hand, use only one-and-a-half acres per person.

"The website added insult to injury by informing me that, if everyone lived the way I do, we would need 4.7 planets. Even people like us, who try to live what some consider to be a relatively simple life, are consuming much more than our fair share. It is as if each of us were invited to a party and cut ourselves a piece of chocolate cake that is over five times the size of what our hostess intended as she calculated how much she must bake for dessert."