New York: In the 19th century, major cities faced their own emissions problem: horse manure. With horse-drawn carriages clogging major thoroughfares, cities were burdened with noxious, smelly manure that drew flies and spread disease.
The issue started to resolve itself as internal combustion engine cars grew in popularity at the beginning of the 20th century. Of course, that meant horses, slowly but inexorably, were replaced by vehicles emitting greenhouse gases.
