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.
Most valid point among others in this thread. Although people tend to waste more electricity on other useless thing, mining sha256 or scrypt makes up for 0.0000000000000001% of wasted power in the world