I've heard and read of many data centers that run on solar and wind power to make up for their carbon emmissions/footprint. An example of one of these would be the Hostgator data centers (They run on wind power), you can read up about it
here.
What I've seen other companies do as well is buy carbon credits to make up for their carbon footprint. Carbon credits are a very easy and cheap way for any business to go green without having to make any major changes to their data center. If you don't know what carbon credits are then you can read up about it
here.
Regards,
ford