Data centers are the gigantic, Borg-like assemblages of computers that run everything we take for granted on the web, from email to social networks. They take a lot of energy, because they do all the things, but more than that they take a lot of cooling; keeping data centers from overheating requires up to half of the electricity they draw. Which is one of the reasons that web giants like Google and (it's widely believed) Facebook are moving their data centers to the arctic circle.
Up where it's already pretty cold to begin with, these data centers can vent their hot air directly into the atmosphere. Google's data center also uses cold seawater for even more cooling. It's a bit like asking your barista to pour your hot coffee over some cold ice, although in this case the data center's contribution to the retreat of glaciers in this part of the world is negligible.