So if Btc is survives, it will be forced to be easier to mine (less electricity, less CO2) in the future, or transaction blocks just won't get validated, which will kill the currency. Easier transaction calculations means that the early adopters and those who can control large resources will become fabulously wealthy (this will make a few very happy) and will de-facto be in control, and the result of the Btc experiment becomes just another form of resource destruction benefiting the few.
As a physicist, and an amateur cryptographer, I've been trying to see a way out of this scenario. The power needed for mining is the key and there's no way around that, again, as all miners know. The bitter irony is that all this destruction of fossil fuels by Btc is mainly dedicated to just validating transactions (supporting commerce) - not to producing anything of actual utility/value, like transportation fuel, medical instruments and drugs, food, commodities. By contrast, the fiat currency, say, a 10oz block of silver, after fossil fuel energy is invested in the mining and refining, it remains an energy-free currency. It can be used (as a currency) at will with no more energy inputs. But every time Btc is used, more fossil fuel must be expended to verify transactions. So, purely as a money system, Btc seems intrinsically hostile to the planet.
First, making bitcoins easier to mine won't reduce the electricity used because of the economics: the amount of electricity used will increase until it's cost equals the value of the bitcoins produced.
Second, the concern over excessive use of resources is overblown. The resources used to mine bitcoins are a small fraction of many other financial activities. For example, the cost of printing currency in the U.S. was more than double the cost of mining Bitcoins.
Finally, the cost of mining is not for nothing. It ensures the integrity of Bitcoin. This cost is also present in other monetary systems, and is probably much higher than Bitcoin. The U.S. spends $375 million per year fighting counterfeiting.