In 1971 an environmental and antiwar ethic was taking root in Canada, and I chose to participate. As I completed a Ph.D. in ecology, I combined my science background with the strong media skills of my colleagues. In keeping with our pacifist views, we started Greenpeace.

But I later learned that the environmental movement is not always guided by science. As we celebrate Earth Day today, this is a good lesson to keep in mind.

At...