Now her ideas, once dismissed as anti-business, nestle comfortably on the business pages.

This year is a watershed for green ideas in business. In Ireland, Green Party ministers have turned out to be acceptable not only to voters and Fianna Fail but to many in the business community who see more opportunities than threats in the coming changes. At a Peak Oil conference in Cork this week, the Greens' Eamon Ryan will be joined by the decidedly non-hippy Micheal Martin.

Merrill Lynch unveiled an investment strategy arguing that companies working fastest to reduce their "carbon intensity" will turn out to be the best-managed and outperform the market.

Behind the new pragmatism, however, there has always been an apocalyptic strain to green thinking.

Human activity has driven the world . . . whether you see it as Creation or Gaia . . . to the brink.

The day of reckoning is nigh.

Until the more pragmatic brand of green thinking we've seen lately, the apocalyptic vision was a key way of motivating people to change their behaviour. Whether it's Al Gore's climate movie An Inconvenient Truth demanding little more than a change of lightbulbs, or the protestors outside Heathrow Airport demanding an end to air travel, the basis of the appeal is a moral one: we caused this problem. And if that doesn't convince you that we have a responsibility to solve it, perhaps the threat of doomsday will. It's no coincidence speeches from many environmentalists eerily echo medieval sermons about hellfire and eternal damnation.

Even now, behind the plans for shiny windfarms, solar panels and biofuels, that narrative . . . and the perverse thrill of contemplating destruction on a massive scale . . . still has power. There's evidence that even the greatest eco-sinners of all, Americans, seek redemption.

All summer, US bestseller lists have been topped with a surprise hit that takes as its starting point our total extinction. The World Without Us, by Alan Weisman, sketches an Earth in which humanity has disappeared. Not in a long, drawn-out climate collapse that takes the planet's other species with it. Just us. The cause isn't what concerns Weisman. A 28 Days Later type virus that wipes out humans works just as well as a Book of Revelations-style Rapture.

As someone who has spent his career covering everything from disappearing ozone over Antarctica to disappearing ice cap in the Arctic and lots in between, Weisman is interested in what would happen next. He paints an expert picture of what happens . . . and how long it would take for evidence of our existence to fade.

It would take just days, he predicts, for the New York City subway system to flood, once its 800 pumps stopped working. In a few years many of its streets would collapse. In a few decades, Manhattan Island would once again be home to coyotes, deer and bear.

While within 20,000 years, most artefacts of human experience would be wiped away, some would remain. Ceramics and bronze would last. But mostly, the billion tons of plastic we've produced would stick around . . . because no microbe has yet evolved to break them down.

Reviewers . . . and millions of readers . . . have found Weisman's post-apocalypse strangely comforting. The planet will get along fine without us, thanks.

His conclusion is that, in order to really reduce our impact on the environment, there needs to be less of us. So we should just stop having children. Or at least limit each couple to one child. In that case, the human population would drop to just over 1bn in decades.

It's prompted a revival of some less comforting thinking, like the Voluntary Human Extinction Movement, which asks people to "stop breeding" altogether.

If this kind of thinking gains popularity among greens, mass suicide instead of redemption, you can keep your Kool-Aid and count me out.

The coming conflict between our desire to save the planet and our survival instinct is one that pioneers like Anita Roddick have seen coming.

"It's going to be an interesting one, the environment versus human rights, " she told me in an interview last year.

She was clear where she came down: "For me it's always human rights and it's poverty eradication."

Amen.