One of the early developers of the bitcoin code, Martii Malmi, has published his correspondences with Satoshi Nakamoto.
In his messages, Satoshi speculated that bitcoin could consume a lot of energy because of Proof-Of-Work (PoW).
“PoW is the only solution to make electronic money in P2P work without a trusted third party….. I believe that if it did start to consume a significant amount of energy, it would still be less wasteful than the labor- and resource-intensive traditional banking activities it would replace. The cost would be an order of magnitude less than the billions in bank fees that pay for all those brick buildings, skyscrapers and junk mail for credit cards,” Satoshi wrote in May 2009.
“Ironic if we end up having to choose between economic freedom and conservation,” he added to Satoshi.
He also didn’t want bitcoin to be promoted as an investment.
“… I’m not comfortable directly saying: consider it an investment. It’s dangerous to say that and you should remove that clause. It’s fine if they come to that conclusion on their own, but we can present it (BTC) that way,” he stated.