During this period he wrote at least one letter to “the mother of modern environmentalism” Rachel Carson. (I’m still on the hunt for any evidence that she ever replied. If you know, let me know.)
Below is a quote from Merton’s journals around the time that he was trying to get a copy of Carson’s book Silent Spring.
Someone will say: “You worry about birds. Why not worry about people?” I worry about both birds and people. We are in the world and part of it, and we are destroying everything because we are destroying ourselves spiritually, morally, and in every way. It is all part of the same sickness, it all hangs together.–Thomas Merton
The Journals of Thomas Merton, Volume 4 (1960-1963) edited by Victor Kramer (HarperSanFrancisco, 1997, p. 274f)