My sense of popular mood about global warming is that the mass of private citizens is desperate for any organisation or individual to speak up and lead in some way. Librarians are used to being a source, not a voice. Any policy statement directed at governments, whether from ALIA or libraries, would have little impact if it wasn’t accompanied by public pronouncement and demonstration of that policy. I’m picturing libraries auditing their environmental impact (as Michael suggested inc comments), making changes, and then promoting their environmental stance and the measures they are implementing. See, for example, the Green Office Guide.  
Our patrons take part of their identity from their membership of a library-using community – just as people do for any brand, activity they engage with. If libraries model environmental behaviour as well as pronouncing our policy positions, we will:
 

• attract new users
• affirm the values of many existing patrons
• revitalise the place of libraries in the public sphere and as a resource for social movements
• increase access to information on environmental topics

Further to this, I’ve recently posted on a New Matilda article by Janet Hartz-Karp.
So creating an impact and taking a lead requires the coordination of advocacy, policy, promotion and engagement. Not to mention individual bravery! I’d really like to hear how your colleagues and superiors respond to environmental issues raised at staff meetings. I had a bit of a cricket-chirping, tumbleweed-blowing-past moment at a recent staff meeting when I did this, before looking to the biblioblogosphere.