What does "removal from nature" mean though, exactly?
I suppose we'd have to hire some analytic & environmental philosophers to sort that out for us.

In the meantime, we could make do with our commonsense understanding of the phrase as a useful heuristic, no?
Edit: whoops, didn't realise there was a whole other page to this thread.
2nd Edit: Here are some really elementary (i.e., not too esoterically academic) quotes I dug up and used not long ago:
The revolutionary change from a food-gathering to a food-producing type of economy made possible the next stage in humankind's cultural evolution, riverine civilization. ... Historians do not agree on how best to define the term civilization. But most would accept the view that a civilization is a culture that has attained a degree of complexity, characterized by urban life. In other words, a civilization is a culture capable of sustaining a great number of specialists to cope with the economic, social, political, and religious needs of a large social unit.
From Palmira Brummett, Robert R. Edgar, Neil J. Hackett, George F. Jewsbury, Alastair M. Taylor, Nels. M. Bailkey, Clyde J. Lewis, and T. Walter Wallbank (Late), Civilization: Past & Present, 10 ed., vol. 1. (New York: Longman, 2003), 10.
By culture I mean the whole of any society's knowledge, beliefs, and practices. Culture is everything: from veganism to cannibalism; Beethoven, Botticelli, and body piercing; what you do in the bedroom, the bathroom, and the church of your choice (if your culture allows a choice); and all of the technology from the split stone to the split atom. Civilizations are a specific kind of culture: large, complex societies based on the domestication of plants, animals, and human beings.
From Ronald Wright, A Short History of Progress (Toronto: Anansi, 2004), 32-33.
Seems to me that 1) the genera-species distinction between "culture" and "civilization" respectively, and 2) the etymological link to cities ("civitas"), are good places to start for a definition. Furthermore, plant and animal domestication is another interesting aspect of "distance from nature," along the lines of that imported Polynesian grass mentioned above.