Horse . . In the early years of the 20th century, horses were causing so much pollution with their peep that automobiles were seen as the "green" alternative,. Just a clarification. Because there was poop all around the place, not related to 21st century understanding of 'green' Horse In the early years of 20th century horses were causing so much pollution with their peep that automobiles seen as "green" alternative Just a clarification Because there was poop all around place not related to 21st understanding 'green'