Environmental history requires a knowledge of the physical and life sciences, social movements, politics, economics, and religion. It is rarely simple, and sometimes raises profound moral questions. Three recent works for popular audiences on environmental topics show how well, and how badly, it can be done.

The field grew up along with the environmental movement itself in the 1960s and 1970s. Early works like Alfred Crosby's Columbian Exchange (1972) and Donald Worster's Dust Bowl (1979) coupled historical analysis with environmental advocacy, deploring the human impact on the natural world. Inverting a long historiographical tradition of celebrating human achievement, they denigrated it as predatory and destructive. The authors' indignation burns through on every page, which makes reading these books an emotional experience.

One implication of this early approach was that nature is best when least affected by humanity. To some historians, as to some environmentalists, wilderness became an ideal, so that the history of America since Columbus could be seen as a tragedy in which a once-­pristine wilderness was systematically destroyed. Native Americans, in this telling, lived in harmony with nature, representing a laudable alternative to European exploitation and manipulation. The concept of the ecosystem, central to the science of ecology in the mid-­20th century, coincided with this vision. It posited an equilibrium state that sustains itself indefinitely unless some external force, often human, blunders in.

This way of thinking about the world has still not entirely disappeared, but historians and ecologists have been chipping away at it for 30 years. First, historians of Native Americans showed that their impact on the natural world was extensive-­from a wave of extinctions upon their arrival ten or twelve thousand years ago to manipulation of the landscape by fire and hunting techniques. Shepard Krech III showed that the idea of "the ecological Indian" was a myth. William Cronon and others added that what we now call wilderness areas had to be cleared of their human inhabitants before they could be so designated. Wilderness, in other words, was one of the products of civilization, rather than its antithesis.

Second, experiments in a wide variety of settings cast doubt on the assumption that ecological equilibrium was normal and undermined the centrality of the ecosystem concept. In its place, "disturbance" took on a new importance. Humans could be the agents of disturbance but so could wind, ice, flooding, variations in animal population, evolution, and geological forces. The ecologists T. A. Pickett and P. S. White suggested "patch dynamics" as a new organizing principle, in which patches of ground might enjoy moments of stability but in which irreversible change should not be seen as aberrant.

Third, the linguistic turn in the humanities in the 1980s and 1990s also brought concepts like "nature" and "wilderness" under intense scrutiny. In The Social Creation of Nature (1992) Neil Evernden pointed out that what we call "nature" is itself a cultural creation, very different from the raw materials out there in the world. To study the history of the idea of nature is to discover that it has meant completely different things in different times and places.

Environmentalists meanwhile disagreed about important questions. Radical "deep ecology" groups like EarthFirst! shouted, "No compromise in defense of Mother Earth." Social ecologists like Murray Bookchin answered that the whole point of environmentalism was to protect the world not for itself but for its human inhabitants. Richard White pointed out that most environmentalists were prosperous urbanites who thought of nature as a place for recreation, whereas economically hard-­pressed farmers and loggers encountered it as a zone of work, which led to very different attitudes. Some point of reconciliation, he argued, should be sought if the two sides were to move beyond mutual recriminations.

Environmental activists disagreed not only on theoretical issues, but also on practical ones. Should forest fires be permitted to burn out of control, as they would "naturally," or should we extinguish them? Should we favor nuclear power as an alternative to smog-­producing coal, or should we shun it as a terrifying outgrowth of the nuclear weapons industry? These were questions on which reasonable people could disagree, but also ones that aroused passionate emotions. They added to the growing awareness that environmental issues are often ambiguous, and that to present them as simple conflicts between right and wrong is to falsify a complex reality.

One of these ambiguous topics-­changing ideas about nuclear power-­is the subject of a new documentary film, Robert Stone's Pandora's Promise. It follows a group of environmentalists who campaigned against nukes in the 1970s and 1980s, the era of accidents at Three Mile Island in Pennsylvania and Chernobyl in the Ukraine. Nuclear power stations, they said, were expensive to build, shrouded in secrecy, linked historically and technologically to nuclear weapons, vulnerable to nuclear terrorism, and had an intractable waste disposal problem.

Now, however, these same men and women hold exactly the opposite views. They are convinced that the safety issues have been addressed in improved designs, that the waste disposal issue is manageable with "dry cask" technology, and that nuclear power stations are actually contributing to world nuclear disarmament by using decommissioned ex-­Soviet warheads for fuel. Traveling with Geiger counters, they find many ostensibly "hot" zones, such as Chernobyl twenty-­five years after its disaster, surprisingly free from high radiation levels, and they concede that they once overstated the danger of radioactivity.

Mark Lynas, a global-­warming blogger and one of the central figures in the film, visits Fukushima Daiichi in Japan, where a tsunami flooded the nuclear reactor in March 2011, causing part of it to explode. Even there he is convinced (after what he describes as a slight "wobble") that greenhouse-­emission-­free nuclear power is the best and safest technology for the future and the best antidote to global warming. He nominates France, 80 percent of whose electricity is nuclear-­generated, as the "greenest" country in Europe, with the smallest carbon footprint. Viewers who disagree with the film's conclusions, as many will (including me), can nevertheless find it well made, intelligent, and plausible. Stone understands that there are strong "green" arguments in favor of nuclear power, and strong green arguments against it.

Another recent documentary, Mark Kitchell's A Fierce Green Fire is far less satisfying. Using Hollywood celebrities as narrators, it divides American environmental history into five simplistic melodramas. In each one, viewers are presented with a handful of admirable people and asked to believe that they have struggled heroically to rescue a world despoiled by powerful and greedy scoundrels.

Visually it is seductive, beginning with some spectacular "eco-­porn" (magnificent elephants, mighty mountain peaks, stupendous waterfalls). It also includes fascinating footage of Greenpeace daredevils taking on Russian and Japanese whalers in Zodiac boats, and of the large-­scale destruction of the Amazon rain forest.

Intellectually, however, it is childishly simple-­minded. Kitchell avoids the difficult questions his material ought to raise. He implies, for example, that global warming is catastrophic, that it is entirely human-­induced, and that there has been no intellectually honest disagreement on these points since James Hansen first proposed them in 1988. Actually, all of these implications are dubitable. He also asserts that Hurricane Katrina was an effect of global warming, a view denied by most meteorologists.

He presents the Kyoto Treaty as a heroic attempt to mitigate warming that was defeated by shortsighted American politicians. He mentions none of the issues that proved divisive there, such as that the dirtiest industrial nations, including China and India, were exempted from compliance. The reasons for this exemption show how difficult the negotiations actually were. Developing nations bristled at the idea that they should be denied the chance of achieving the same standard of living now normal in the West, and said that they could not deal with the greenhouse effect until they had overcome mass poverty. American politicians reacted by declining to ratify the treaty, which may be regrettable but is hardly surprising.

Much more rewarding, and much more realistic, than A Fierce Green Fire is Adam Rome's new book The Genius of Earth Day. It asks where the idea of a national environmental awareness event came from and why it was so successful. Late in the 1960s Senator Gaylord Nelson (D-­WI) conceived the idea of an environmental "teach-­in," borrowing the concept from the anti-­Vietnam-­war movement. His top-­down organization, which planned the event for April 22, 1970, coincided with an immense surge of bottom-­up activism, creating a moment of synergy that permanently changed Americans' ideas about the environment. Far more groups participated than Nelson had dared hope, with high schools, churches, and civic groups joining the colleges he had originally targeted. On the day itself 12,000 events across the nation involved millions of citizens, more than had ever participated in civil rights or anti-­war protests.

Rome understands that this kind of enthusiasm cannot spring to life overnight, and in a fine early chapter he explains the many sources of concern that contributed to Earth Day's success. Among them was the liberalism of the 1950s and 1960s, which was reacting to what John Kenneth Galbraith called the problem of social imbalance-­the co-­existence of private wealth and public squalor. Also important was the rise of a generation of scientists, such as Barry Commoner, who stepped out of their laboratories to participate in public policy debates. Educated middle-­class women objected to the hazards (radiation and pesticides) confronting their children. Young people, many of them at least touched by the hippie movement's rejection of an inauthentic "plastic" world and eager to "get back to nature" were receptive to the new message too. So were conservation organizations, most of which had started out narrowly focused on fish, birds, or national parks, but now began to broaden their agendas to protest against overpopulation, pollution, and resource depletion.

Rome's presentation emphasizes the confluence of issues and groups at a politically propitious moment. Although he is clearly sympathetic to Earth Day and to the participatory democracy it embodied, he can also understand the skeptics who rejected its message. Among them were African-­American and new left groups who thought of it as a distraction from the unresolved "sixties" issues of war, poverty and discrimination.

History is a discipline because it has a set of procedures that need to be learned, often slowly and painfully, and whose logic is not always clear at first. It includes learning the self-­discipline to avoid turning complex realities into simple struggles between right and wrong. Among these three, Stone and Rome are persuasive as environmental historians because they show how movements arise and change, how new issues affect old certainties, and how often outcomes differ from participants' original intentions.

—Patrick Allitt is Cahoon Family Professor of American History at Emory University and author of a forthcoming history of the major environmental debates in the US since World War II.