Sorry for the delay in responding; I haven’t spent a lot of time here of late (lots going on at work ;-).
If I had to generalize, science/pure math degrees are more accepted than liberal arts degrees for most of the technical aspects of sustainability, i.e. performing life cycle cost analysis or comparing systems for efficiency and things like Return On Investment, because you often need to perform calculations and unit conversions and the like and evaluate the technical claims of sometimes competing solutions.
But for advocacy (under which I include everything from lobbying to eco-tourism) I would say any college degree is fine, because what is really needed here is a superb ability to communicate, either verbal or written or even better, both skill sets AND a passion for protecting the long term viability of the planet as a healthy ecosystem for all organisms. It only helps if you have a science credential AND can communicate well because then you have an area of expertise that you can use to help illustrate the impacts of un-sustainable practices to those you want to educate and affect their behaviour.
At the end of the day, the higher profile the position, in terms of speaking to audiences with lots of influence, the more credentials matter and doctoral degrees are the standard for heading up NGOs or Federal and State Departments engaged in policy work.
I would think you could refine your search by combing your specific interests (are you a habitat person, an energy nut, a transportation kook, etc.) and then learn everything you can about the impacts of that area and what are some emerging ideas to address some of those impacts.
Or, like some I know, become the sustainability looney in your existing place of employment (if you are still employed) and make it your ulterior plan to become that company’s sustainability director or guru or whatever. You do this by reading everything you can on the myriad of sustainability issues across nearly every aspect of your company’s operations (on your company’s dime if you can swing it, on your own time if not). You become a generalist but one that also brings a passion for the discipline of Sustainability.
You can often justify your new position by demostrating that often sustainable means cost savings as well as fewer negative impacts on the planets ecosystems and the organisms that live in them.
And, lastly, if it’s not already obvious, “walk the walk and talk the talk” in your everyday existence as much as you reasonably can with out going overboard. What I mean by that is gauge your own behaviour vs. your peers and see how you stack up lifestyle-wise. I think way back we had a thread where we described some of the stuff we did to lessen our un-sustainable impacts and talked about where we wanted to be personally in the future.
Hope this helps.
BTW- search Google for bios of “sustainability director” positions and see what their CV’s look like. You can start with ours-
http://berkeley.edu/...01/30_mcneilly.shtml
Cheers!