The Overton Window is a memetic engineering concept in use among political wonks, but with broader applicability. Wikipedia describes it thusly:
It describes a "window" in the range of public reactions to ideas in public discourse, in a spectrum of all possible options on an issue. Overton described a method for moving that window, thereby including previously excluded ideas, while excluding previously acceptable ideas. The technique relies on people promoting ideas even less acceptable than the previous "outer fringe" ideas. That makes those old fringe ideas look less extreme, and thereby acceptable. Delivering rhetoric to define the window provides a plan of action to make more acceptable to the public some ideas by priming them with other ideas allowed to remain unacceptable, but which make the real target ideas seem more acceptable by comparison.
The resulting spectrum is, then:
Unthinkable Radical Acceptable Sensible Popular Policy
This is a familiar notion, but with a formal name. In the US, movement conservatives have used this technique to great effect, but it's now starting to show up in discussions among progressives/liberals.
I think that the Overton Window model could prove to be a decisive tool for shifting perspectives in the US about environmental risks, and in fact provides a counter-argument to the "Village Green" types who claim that extreme eco-rhetoric is damaging to the environmental movement.