At one point when I was at AOL, we had 'green' blogs for several different content verticals, whether they be home improvement, autos, careers, tech, finance ... the list went on and on. They often were chasing the same stories and never built much of a following.
In some ways, this was a reflection of the 'green washing' that has gone on at least for the past decade, where things like corn-based ethanol are touted as an environmentally-friendly solution to something that is inherently not green at all.
That is not to say that there isn't real progress being made in the 'greening' of America. But some of the concepts just didn't make a lot of sense as content categories.
Perhaps an exception to this would be something like the movie 'No Impact Man' where one writer takes some of these ideas to the extreme. But even something like this has a limited appeal to a broad audience.