Find a section that indicates that Bradbury was an early environmentalist FAhrenheit 451 part 3 pages 154-165no
I do not seem to have the same edition of the book as you do, so I cannot be sure that what I see comes from the pages you cite.
I think that the section you are being asked to identify lasts from around the time that Montag jumps into the river until the time that his foot hits the railroad track. In between there, I think that you can argue that most of the text shows an environmental consciousness.
During that part, Montag drinks in all the sights and sounds of nature. Bradbury describes in loving detail things like the smell of the leaves. These kinds of passages are implying that nature cleanses the soul, which is what many environmentalists say.