Walt Kelly’s little cartoon possum Pogo turned out to have been a sage observer, and adviser, for much of the 20th century. This classic cartoon, on the second Earth Day, in 1971, well summarizes the problems of pollution, making historical allusion to that famous message from Master Commandant Oliver Hazard Perry after the Battle of Lake Erie in the War of 1812: “We have met the enemy and he is us.”
It is a mark of what the internet lacks that I could find just one quick copy of this cartoon on my first search. All of Kelly’s work should be available, but it’s largely missing from internet searches. I’m sure this is still under copyright, but I haven’t yet found the information.
Oh, of course: The line is too good to have been used just once. Kelly used the idea for the quote in the forward to a book in the 1950s, and used it on a poster for the first Earth Day. The famous comic strip followed in 1971.