In the early years of the 20th century, horses were causing so much pollution with their poop that cars were seen as the "green" alternative.
What on earth could've been worse pollution wise, than cars? In the 20th century, many were traveling by horse. Either riding the horse or by carriage. Because this was the main way of transportation, horse poop became a massive problem. Pun intended. It caused way too much pollution that cars were considered a green alternative!