Only a tiny fraction of the power goes into performing transactions; the total power consumed is independent from transaction rate. Bitcoin in 2009 used vastly less power than today yet had the same transaction capacity. The power consumption scales with the price of Bitcoin[1], which is determined by demand and most of the demand right now is driven by future price speculation.

Interestingly, the new cash-settled CME Bitcoin futures contracts, due to start trading in December, will allow speculation on the future price to take place without requiring possession of actual Bitcoin. These futures may both increase Bitcoin adoption and reduce the upward pressure of speculation on the price.

[1] More accurately, the value of power consumed for mining Bitcoin approaches the value of the block reward plus transaction fees.