Our central aim must be to create widespread, mainstream cultural change. But what the Overton Window teaches us is that this cultural change sometimes happens by advocating for what is currently “politically unacceptable”. It’s a tactic that the right wing of US politics has used effectively for some time, pushing ever stronger and more extreme memes, and in doing so they have shifted the center of gravity further to the right. It’s not that mainstream independents and moderates suddenly agree with Glenn Beck (who incidentally wrote a novel called the Overton Window), but rather that they find their views gradually shifting due to the pull of his extreme rhetoric.

So what does this mean for environmentalism and the fight for a sustainable economy? It means we should probably stop worrying quite so much about what is, and what is not, politically realistic.