hen I was a young campus activist at Dartmouth College in the early 1970s, the issues of environmental degradation were clear. DDT was the nation's most popular pesticide, spread widely on farmlands to protect crops and in cities to control mosquitoes and Dutch elm disease. To ensure smooth engine performance, lead was added to gasoline and emitted as an air pollutant from the tailpipe of every car and truck in the United States. Phosphate was the basic active ingredient in nearly all detergents and in sewage effluents entering lakes and streams throughout the country. With all good intentions, we directly mined or manufactured these substances and added them to products designed to improve our daily lives--"better living through chemistry."

Subsequently, when environmental scientists found these substances were polluting the environment, appropriate regulatory procedures were obvious. The costs and risks of inaction were deemed unacceptable compared to using safer alternatives. And despite corporate objections, less harmful alternatives were found--many with significant profit potential for their inventors.

Today, bald eagles have returned to nest in most areas of the United States, where just a few decades ago, DDT residues had rendered their egg shells too thin for successful incubation. Urban children show lower levels of lead in their blood, and lower levels of lead are transported through the atmosphere and deposited in remote locations. Whitefish have returned to Lake Erie, which now seldom suffers the nuisance blooms of algae that choked its waters in the 1960s. Nearly all Americans enjoy clean air and water and, despite corporate warnings to the contrary, our crops still grow, our cars still run, and our clothes are still clean.

Instead of being able to bask in these successes of the environmental movement, however, the American public now is faced with a baffling array of new environmental issues much more complicated than the problems we faced thirty years ago. Scientists recognize new threats to the biosphere--the fabric of natural ecosystems and the diversity of plants and animals that inhabit them. Unlike the obvious, toxic pollutants that spurred the environmental movement of the Sixties, we find that six billion humans on Earth, each in the pursuit of a higher standard of living, also cast subtle, diffuse, and long-term effects on nature.

Where we once focused only on the direct emissions of ozone as an air pollutant in cities, we now find that the forests of the eastern United States are often bathed in harmful levels of ozone, formed by the reaction of volatile organic compounds from the trees themselves with nitric-oxide gases emitted by fossil-fuel combustion and fertilized soils. Scientists have unraveled the complex photochemical reactions--that is, reactions mediated by sunlight--that form ozone in rural environments. We now know that the area affected by ozone pollution embraces more than just our cities. Rather than capping the obvious emissions from a smokestack, efforts to develop appropriate regulatory procedures to ensure safe ozone levels must involve broad participation of our citizenry.

Environmental scientists also tell us that rising carbon dioxide in Earth's atmosphere will lead to changes in climate that will disrupt much of our current social and economic system. But rising levels of this odorless, colorless, and unreactive gas are easy

to overlook. No one wakes up in the morning and says, "Gee, the carbon dioxide level is awfully high today." Because it is well-mixed in Earth's atmosphere, each molecule of carbon dioxide (CO²) contributes equally to the problem--whether it is emitted in Durham or Daulpur. Because each molecule added to the atmosphere is destined to remain there for decades, it will contribute to global warming well into the twenty-second century. Rising CO² in the atmosphere and climate change are long-term and global issues. Derived from the consumption of fossil fuels that drives nearly all of the world's economy, emissions of CO² will prove difficult to regulate.

When faced with complex and baffling issues of our own health, we trust the wisdom and treatment recommended by highly trained doctors. Self-interest makes us listen to their advice. We may be curious about the levels of our blood chemistry, but few of us question how our doctor interprets the lab report. For centuries, we have held medicine among the most honored professions. The reputation of a good doctor travels fast, even in the world of managed care. Why don't environmental policy-makers--today's environmental health professionals--enjoy the same stature?

Strangely, despite increasing evidence that our own well-being is dependent on environmental health, self-interest often determines a different human behavior relative to environment--we act as if we are above nature, not part of it. For ourselves, doctors tell us the risk of smoking vastly exceeds the pleasure of doing so. But our love of large, low-mileage vehicles and our demand for low gas prices suggest that in issues of environment, we focus on today's pleasures rather than tomorrow's risks. Few voters link low gas prices to high gasoline consumption and to the urban sprawl that destroys natural land. Exploitation of nature is driven by short-term, personal economic reward, derived from a world that depends on the natural diversity of plants and animals to ensure the long-term stability of environmental conditions--clean air and water--that we take for granted with each new day.

In the face of an increasing onslaught and complexity of environmental issues, we will make only limited progress in protecting the environment until we have a cadre of highly trained environmental scientists who understand how the world works, policy-makers who can advise us on the best solution to environmental problems, and a citizenry that respects their judgments. But scientists and policy-makers have a poor track record of communication, because the training in one field has seldom included an appreciation of the other. Scientists must recognize and understand the complexity of environmental issues, engineers must develop solutions, and policy-makers must understand the magnitude of the threats so as to balance the risk of inaction against plausible alternatives. Most importantly, the public must have a basic appreciation of how nature works, so as to demand appropriate action.

As our population continues to grow, never before has there been a greater need for broad-based and interdisciplinary environmental education for our citizens. When I was a young environmentalist, the questions were obvious: How does nature operate and what impact do humans have on natural systems? Certainly, important scientific research remains to be done to improve our answers to increasingly complex environmental questions, but there is ample cause for immediate action on a large number of environmental threats that face us. When the scientific certainty approaches 95 percent, inaction leaves the world on a path that is increasingly difficult to change and frightening to those who know the prognosis for exponential population growth and resource use in a finite environment.

We must listen to environmental scientists and to their interpretation of our planet's lab report--recording changes in the chemistry of our atmosphere and oceans, and losses of the diversity of species that maintain the fabric of our natural ecosystems. Just as we respect the family physician, we must follow the regimen offered by professionals.