" A 1972 study showed that the amount of pollution per mile traveled by horse was a hundred times the amount of pollution per mile traveled by automobile.27 Since the cars produced in later years have had reduced pollution levels, the disparity today would be even greater. It should also be noted that the replacement of horses by automobiles made it possible to “restore more than 80 million acres of forestlands that had once been cleared for horse pasture.”28 "

― Thomas Sowell , Economic Facts and Fallacies