Mainstream economics has attempted to become a value-free 'hard science', but ecological economists argue that value-free economics is generally not realistic.

These are the mainstream new resource economists, the new environmental pragmatists, and the more radical social ecological economists.

International survey work comparing the relevance of the categories for mainstream and heterodox economists shows some clear divisions between environmental and ecological economists.

While Clem Tisdell is commonly recognised as an ecological economist, his research interests are diverse.

One approach, now popular among ecological economists, is to calculate energy balances on the assumption that energy supplies represent the ultimate constraint on human activity.

And ecological economists are not any better at predicting how these limits will impinge than garden-variety economists.

Tim Jackson is a British ecological economist and professor of sustainable development at the University of Surrey.

That idea, which puts increases in productivity into new prospective, comes from Joshua Farley, an "ecological economist" who was interviewed this week on WorldChanging.com.

A number of ecological economists claim that industrial civilization has already "overshot" the carrying capacity of the Earth, and "smart growth" is mostly an illusion.

"We create our own history," said Ms. Armstrong, who works as an ecological economist at the Regional Plan Association.