I have already written detailed analysis on this. It comes down to perspective. The total power consumed for Bitcoin mining is a matter of perspective. From the position of the miners, power consumption is outrageous as the network fees fail to cover the mining costs of the coin. Without the continual appreciation in price and block chain rewards the business model would be one destined for failure.

If you compare its power consumption to say that of the US, it's more like comparing the Great Lakes the the entirety of the worlds oceans and really is not that much at all. I read that the total power consumed by bitcoin mining is less than the power consumed by all devices in the US on standby. For in depth reading on the subject see the following two articles.

https://steemit.com/bitcoin/@pawsdog/is-bitcoin-really-decentralized-or-are-we-being-led-like-lambs-to-the-slaughter

https://steemit.com/bitcoin/@pawsdog/need-mathematical-help-mining-costs

Lastly as shameless self promotion read this one.

https://steemit.com/steemit/@pawsdog/steemit-quest-for-one-million-time-required-to-build-a-usd1-000-000-00-steemit-account