I was just thinking that there may be a solution for electricity consumption when mining bitcoins that I obviously don't know about, or maybe something related to what you mentioned about the reformed energy.
Bitcoin's security is based on Proof of Work. Miners are incentivised to mine by the block reward and the transaction fees - the electricity used is based on how much money is available, which is the combined value of the block reward and transaction fees.
Alternatives to PoW include Proof of Stake and mixed systems. However, garnering consensus for any specific solution would be very difficult, and PoW has proven very secure over the nine years that Bitcoin has existed.
Bitcoin is insignificant when it comes to considerations of pollution.
Per transaction, it's pretty significant. If it was used by more people and/or the price was higher, it would be very significant overall.