After a few extremely icky incredibly stoopid conversations I've had within our otherwise lovely field populated by mostly smart people, it is with great trepidation that I enter publicly into this fray. I'm mainly doing so since I like you folks. People that don't like what I have to say can bite my shiny metal arse. 
How do we know that our presenters are white? Did we ask folks to self identify after giving their talks? Before? Or, perish the thought, are we using the Scott Brown test? I really dunno, since I haven't presented at your Conference. (Or even attended.) I was fortunate enough to have a clerk that self identified black but looked like Barbie. Folks tended to treat her as if she were very confused until they met her father. So if we're not actually asking, perhaps we are wrong in our aessessments.
I think it's a happy thing that this conversation started up, but please tread with care.
Statistics are great, but if we just look at the numbers, we might just be perpetuating the self perpetuating problem. If you want to improve your climate, then shoot for a reflection of society in general. Discussing issues important to minorities is still the best way to get folks interested and involved.
There was a question posed at the very beginning of the Wikimania conference in DC that caused me to approach the person that had asked it. That person then held my hand, sometimes in a truly awkward and embarrassing fashion, for the entirety of the conference and beyond. I couldn't help but feel completely welcomed for most of Conference despite being a n00b. The oddest part of that group was that the folks I ought to have felt most welcome around I felt alienated me the most.