This coming week, world leaders will descend on New York City to attend the United Nations General Debate. Before the speeches get underway, Secretary-General Ban Ki-Moon will host the U.N. Climate Summit, where he and his officials will pitch climate change as a development issue and environmental reform as an investment opportunity. "This is not about dividing up the pie of pain, but about growing the pie of opportunity,” said Assistant Secretary-General for Policy Coordination and Strategic Planning Robert Orr during a press briefing this week.

Inside U.N. headquarters, over 120 heads of state and executives from multinational corporations—like Wal-Mart, McDonalds, and petroleum and oil industries—will commit to being more environmentally conscious. Outside headquarters, however, the environmental movement has support from perhaps an even less-likely supporter: unions.

Labor is conventionally seen as an antagonist to “job-killing” environmental measures. In 2011, Laborers International Union of North America (LIUNA) President Terry O’Sullivan accused two unions that opposed the Keystone XL pipeline of being “under the skirts of delusional environmental groups which stand in the way of creating good, much needed American jobs.” “Highly publicized conflicts have led to the perception that environmentalism and unionism do not mix,” write Richard Kazis and Richard L. Grossman in their 1982 book Fear at Work: Job Blackmail, Labor, and the Environment.

But this antagonism, as Kazis and Grossman show, overlooks some crucial episodes in the environmental movement’s history.

Take the southwestern Pennsylvania factory town of Donoroa, where, in the 1940s, smog was a fact of life. Residents were accustomed to breathing toxic air the consistency of pea soup. They were used to sweeping off layers of dust from their cars and window sills. One week, in late October 1948, the air became even worse. For two days, visibility was so poor that driving was impossible. One father used a flashlight when he walked his little girl to school in the morning. But this was before air pollution was widely understood to be a health hazard, and regardless, the U.S. Steel plant emitting the smog provided jobs. It took a couple days and a rainstorm for the smog to thin, but by then, 20 people were dead, 6,000 of the town’s 13,500 residents were ill, and a few hundred had fled. Calling the dense smog “an act of God,” U.S. Steel refused to admit liability.