That's a good side topic to the thread. I think the studies would have to be very detailed and encompass many factors, including environmental impacts, to make a valid conclusion on how green digital is compared to paper.
My guess is that digital would be found to be greener, but I bet it is a close race. The server farms should be getting at least 50% of their power from renewable sources like solar and wind. Digital output requires energy and chemical intensive devices to make it usable, PC's, phones, tablets, pads, etc.
How many times can paper be recycled? Does it chemically degrade to the point where it is no longer suitable for print materials? I suppose it may depend on what tactile and visual characteristics the distributor is looking for, but newsprint for example, can it go round and round more or less forever?