The use of electrical power to secure the network, and an increase in doing so fueled by the greed of miners (I'm one of them). The calculations completed have no intrinsic value - they're just a means to the end of securing the network. As time goes on, if bitcoin continues to succeed, power consumption will continue increasing.
Except that for many miners (like me), power usage hit a peak and is now on the way down even with increasing GH as I replace older less efficient miners with ASICS.