Over the years, I've heard many very wrongheaded ideas about the environmental cost of living space.
One set of people seemed to believe that city living is more destructive to the environment than country living, because cities are hugely destructive to the environment, more than houses in the country. This used to be a popular idea, and many of my friends had the idea they'd eliminate their harm to the environment by living far out in the country, far removed from anyone else if possible.
But nowadays nearly everyone recognizes that spreading the same number of people doing the same things out over a larger amount of land would almost by necessity make their living even more destructive to the environment. Human concentration is one of the simplest and best ways of reducing the human environmental footprint. The basic principle is that the more concentrated human activities are, the more undivided space is left to non-human wildlife. That needs to be something we think about and this essay was motivated towards that end.
There are many ways in which this is true (and a few that it might not be*):
1) Occupation. More land may be occupied per person in far out back habitation (and changing any bit of land for human purposes counts as this kind of 'occupation' to a greater or lesser degree...so if I have a long private paved road leading to my far out back house, that entire road counts as part of my ecological footprint per unit of land area nearly as much as my house. Even an unpaved gravel road is somewhat destructive to the environment, though likely somewhat less than a paved road. It is land stolen from nature (wildlife). And then there are fences which may be the worst kind of occupation of all per unit of area they are built on (counting not only as space but despoilment and decimation).
2) Despoilment. Any part of that land where I use pesticides, herbicides, etc, is also 'occupied' and perhaps in the worst way of all, since such chemicals can themselves migrate or cause issues for migratory species. Likewise with growing decorative plants, grass, anything that it not natural or useable by the wildlife in that area, and especially if it is GMO and contains bio toxins (though that specific issue is covered by #3). (Growing crops for human consumption cannot be counted here because it is a social need wherever people live...it has to be done somewhere...but if the dispersed crop growing is done more destructively than otherwise, then that would count as greater damage, or if it is done less destructively, then it would undo a despoilment which would otherwise occur and would be a benefit instead of a cost.)
3) Decimation. More natural space and habitats may be decimated this way. A paved road is not just the space it occupies, but the way it divides what is on the right side of the road from what is on the left side of the road. The now separated spaces are worth less to wildlife than would one wide open space.
4) Transportation costs. Transportation to and from a far out place means that the transportation energy (and other environmental costs) adds an addition factor for all the human goods used to live, or produced for others.
Those are big and pretty straightforward. But there are others
5) Embedded construction transportation costs. Even constructing my far out back home has much greater environmental costs, as all the raw materials and workers must be transported through the surrounding area, causing more Occupation and Decimation by that very process, and giving my home a greater embedded energy cost. Also all the raw material most likely has to travel a longer distance from where it is extracted or prepared for human use--this is not necessarily true, but probably true in most cases nowadays for anything like a modern home (and not an igloo made from surrounding ice).
6) Greater Apriori Ecological Sensitivity
This is not necessarily true. A city might have been built (and possibly long ago) in a very environmentally sensitive place, which for example multiple species might (have) used for migratory, mating, or feeding purposes, so you could argue it is just as environmentally destructive to live there. But often people fantasize or realize living in uniquely sensitive areas even where cities could not be built. Beaches and mountain forests are good examples.
7) Greater Post Hoc Ecological Sensitivity
Cities already exist, and adding one more person might not even cause the existing city to need to physically occupy more land. More vertical space could be added, or any pre-existing space within the city might be better used. OTOH, adding one more person living (in some style anyway) out back is much more likely to make a difference in the space available for wildlife.
Even if the city expands for one new person, the space immediately next to the city was already somewhat degraded for wildlife by the city being next to it. So even if the a priori ecological sensitivity of the surrounding locales were identical, and the same amount of new space were used, expanding the city might still have less Post Facto Ecological Sensitivity that one more person living in the far out back (and all the things I've already described).
Generally, using or even taking advantage of an environmental insult which already exists is less destructive that creating a brand new environmental insult de novo. After some personal meditation on the subject, it seems to me that about half of the environmental cost of a construction for human habitation is due to the agents causing it to be constructed, which may include both the developer and the first buyer for homes built on speculation that they will be sold. Or it could be 100% for an owner built construction that is so unique that it is never going to be used later by someone else (who would share some of the environmental responsibility going forward later). Flipping this around it's clear that anyone occupying a pre-existing home is responsible for much less than half of the environmental cost of its creation, which is further reduced by the lengths of previous (and post) occupation. (This same kind of calculation works for other human artifacts, such as cars. There is much less post hoc environmental harm in acquiring and using a pre-existing car than a new one, then adjusted by other factors such as how damaging that particular car is.)
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Of course there are additional factors regarding how energy efficient it is to operate the home, etc. Those are not part of this discussion which is really just about the spaces and less how they are operated. Presumably energy economy could be achieved either in the city or the country, and it would probably be easier in the city.
* There could also be compensating factors, including living on less (and it would have to be much less , or locally produced/obtained, to compensate for the transportation and other costs), and dispersal of waste to the degree it is better neutralized by natural forces, though such dispersal is not necessarily a good thing either, especially if chemical wastes are involved. Many people do indeed envision their living in the great out back is something they could do with far less, and that could make it a better choice despite all of the above. But often people's vision may not include all the things necessary for comfortable living, which may be most easily obtained in pre-existing housing in cities.