The environmental credentials of cloud computing routinely come under scrutiny, whether it’s environmental campaigners lambasting a data center’s reliance upon coal or proud owners of new data centers pointing out that they’re naturally cooled by glacial meltwater or architectural ideas borrowed from chickens, naturally heated from deep below the earth, or cost-consciously sharing ‘waste’ heat to warm their local communities. The truth, of course, is that some data centers are pretty efficient, and some are very, very dirty. Recent figures from the Uptime Institute suggest an average PUE of 1.8, so there’s still a long way to go. Here on GigaOM, Jeff St. John keeps a close eye on this space, for example commenting on Greenpeace’s data center report cards last month. Elsewhere, Silicon Republic’s Ann O’Dea talks with Tom Raftery of GreenMonk this week. In the piece, Tom clearly argues that the picture is far more complex than environmental campaigners and data center champions typically admit, and he points to some of the areas in which clarity might usefully and achievably be sought. A simple PUE number is no longer enough.