You could call it the Bono effect. Or the Sting effect. Or the McCartney effect. It's the effect of the intervention of celebrity on worthy causes, environmental or otherwise. And one thing you can say about it is that it's certainly effective.
If you were the Pacific Gas & Electric Co right now, you would not only be weighing up your legal options and technical advice about whether or not the new "plume" of contaminated water under Hinkley, California, was yours or not, in trying to avoid another multimillion-dollar settlement with local residents. You'd also be considering the influence of the Academy of Motion Pictures Oscar for Best Actress, 2000, which put the seal on a particular narrative of how you behaved in the past.
The Oscar not only crowned the performance of Julia Roberts as Erin Brockovich in the movie – it cemented an interpretation of Ms Brockovich's struggle with PG&E, in which she was cast as the heroine, and the company as something very unheroic. Davina and Goliath, if you like. It's hard to fight against a narrative which has taken root, especially one depicted by an Oscar-winning movie seen by millions.
Celebrities empower narratives: vegetarianism was seen as cranky until Paul McCartney's endorsement. Bono made the fight against poverty cool, and Sting did the same for rainforest Indians. You can say it's shallow and opportunistic, but it works. PG&E should fear Erin Brockovich, but fear the Julia Roberts effect even more.