The astronomer Carl Sagan was just 62 when he died on the second-to-last day of December 1996. I shook his hand once, when he came to speak to the astronomy club at my high school in the early 1970s.

Sagan was among the first scientists to warn us about the dangers of carbon emissions from motor vehicles and industry, pointing to Venus, where surface temperatures are hot enough to melt lead, as an example of a “runaway greenhouse effect.”

It was Sagan who prevailed upon NASA to have the Voyager 1 spacecraft take the “Pale Blue Dot” photo of Earth from outside the orbit of Saturn, though it had no scientific value. But its symbolic value was immeasurable. Like the Apollo photo of the whole Earth taken by the astronauts on the way to the moon, it drove home the reality that we are all passengers on the same vessel, the Mother Ship, whose resources are vast but not indestructible.

My own environmentalism was spawned and shaped by my childhood on the Maine Coast. I swam in its clear, cold waters and ate food from its ocean, lakes and streams. I also saw open-air dumps, untreated sewage, and beer cans tossed casually by the thousands into the roadside trees. I saw the Santa Barbara oil spill on TV and imagined with horror the same thing happening to my beloved Penobscot Bay.

The world’s population of motor vehicles now numbers approximately 1.2 billion. The United States is by far the worst offender, with five vehicles for every six people. If the Chinese owned cars in the same proportion as we do, they would need a billion vehicles just for themselves.

The average weight of a car or light truck is 4,079 pounds. An average gas-powered vehicle spews its weight in carbon compounds into the atmosphere each year. That means that our automotive infrastructure is annually pumping 4,894,800,000,000 (4.9 trillion) pounds of greenhouse gases into the clear blue sky. (And that’s not even counting the impact of the trucking industry, the byproducts of road construction, and vehicle manufacturing and disposal.) While these gases won’t turn our planet into Venus, they will continue to contribute to rising sea levels, acidification of the oceans, disruption of food supplies, and other life-threatening challenges.

Sagan’s contemporary, paleontologist Stephen Jay Gould, was only sixty when he died in 2002, leaving a lifetime of research and provocative theories, and a trove of extraordinary essays on a wide range of subjects for general audiences. Like Sagan, Gould had the facility to convey complex concepts in ordinary English, and to skewer popular perceptions.

“We pitiful latecomers,” he wrote, “are stewards of nothing in the long run. Yet no political movement is more vital and timely than modern environmentalism – because we must save ourselves (and our neighbor species) from our own immediate folly.”*

The Penobscot River near Bangor was an industrial dumping ground when I was a child; now people swim in it. We regularly see bald eagles from our kitchen window half a mile from downtown. Fifty years ago, they were nearly gone from Maine. These are two great environmental success stories, apparent to anyone who cares to look. By not owning a car, I hope I am contributing, in my own small way, to another.

* from Bully For Brontosaurus, copyright 1991 by Stephen Jay Gould.