On a day when most were simply cursing nature for the impossibly cold temperatures, guest lecturer William Cronon was trying to convince people of the importance of preserving the frigid weather.

In a public lecture Monday sponsored by the History Department and the School of Forestry and Environmental Sciences, Cronon discussed the relationship between American history and the environmental movement. About 65 students, faculty and alumni were crowded into the standing-room only classroom. To describe his theory of how ecology — the study of organisms in an environment — and history — the study of humans and their interactions with the environment — are really two sides of the same coin, Cronon shared an abridged version of the first chapter of his forthcoming book, which has the working title “Saving Nature in Time.”

Cronon is a professor of history, geography and environmental studies at the University of Wisconsin at Madison. He has published a number of books and articles, including “Nature’s Metropolis: Chicago and the Great West,” and received various awards for his research in American history and environmental studies.

Cronon argued that to understand environmentalism, one must also understand the history of humans’ interaction with the environment. He said that movements that hope to change the future have to rewrite history.

“Rewriting history enables us to think differently about how the past got us to the present so that we can figure out where we want to be in the future,” he said. “Environmentalism seeks not only to alter our relationship with nature, but also seeks to alter our relationship with history.”

To explain his point, Cronon described the rewriting of an earlier environmental crisis, that of Dichloro-Diphenyl-Tricholoethane, commonly known as DDT. In the 1960s, he said, DDT was seen as a “miracle substance,” which was remarkably lethal to insects but appeared to have no harmful effects on humans. It was sprayed from trucks in residential neighborhoods to eliminate mosquitoes and soldiers in tropical wars soaked themselves in the chemical to escape mosquito-borne malaria, Cronon said. But in Rachel Carson’s 1962 book “Silent Spring,” a dark parallel history of DDT emerged.

Carson described a happy, healthy community that suddenly discovered it had been poisoning itself for years. Stepping off from this parable, Carson argued that DDT had been endangering the lives of birds, fish and mammals high in the food chain who accumulated large amounts of this chemical over time and who developed nerve damage or suffered reproductive failure. This was an entirely different history of DDT, Cronon said, one that acknowledged that scientific progress was not necessarily good for the environment or good for humans.

The story of DDT, Cronon said, is just one example of the way the recrafting of history — and the recasting of “progress” — can change the way the future looks. He described how progress that led to the possibility of nuclear war changed the psyches of an entire generation of people by recounting his own recurring childhood dream. In this nightmare, Cronon struggled to convince his family to seek shelter from an impending nuclear attack. Although he managed to save himself, he could not find his family in the wake of the explosion and was filled with despair and anxiety when he awoke. Cronon said that when he spoke to others in his generation many of them admitted to having an almost identical nightmare, indicating that “progress” had influenced them unconsciously.

“He was talking about historical events that define a generation more deeply even than just consciously,” Bente Grinde ’09 said after the talk. “He used that to connect it with the history of the environment, which can easily be ignored in the face of what’s called progress.”

Stephanie Ogburn FES ’07 said that Cronon, in his work, has always “asked Americans to think about wilderness not as pure nature, but as something constantly shaped by humans.”

Grinde agreed that “he said some important things that you don’t usually hear.”

Cronon will be giving another talk today entitled “And the Moral of the Story Is…: Fables of Climate Change” at 4 p.m. at the Sage Hall of Forestry and Environmental Studies.