Well, it is done automatically every 4 years :) It is a self-balancing system - more people shout about Bitcoin being dirty -> less adoption -> lower the price -> less energy consumption. Add on top the fact that in 2024 block rewards will fall 50% anyway and someday it will be zero.

I am all for making Bitcoin green(er), but IMHO there shall be no short-termism of the sort "Elon complained + price dropped 40% - lets go radically change things".

IMHO if we want to make BTC cleaner we can add functionality where users can prioritise some miners over the others, with the view that users will prioritise "green" miners and they will get more TX fees, and there will be economic incentive to go green.

On Sun, 23 May 2021, 09:49 James Lu via bitcoin-dev, <bitcoin-dev@lists.linuxfoundation.org> wrote:
Background
===
Reducing the block reward reduces the incentive to mine. It reduces the maximum energy price at which mining is profitable, reducing the energy use.

Bitcoins have value because they are accepted by full node users, from individual node operators, to exchanges and custodians like Coinbase. Anything else and the Bitcoins don't exist and are worthless. Like all currencies, Bitcoin has value because others recognize that they have value.

Idea
===
Reduce the block reward by adding fewer coins to the UTXO set per block. This should be done gradually

Consensus layer
===
This is a soft fork, because it tightens theĀ 

Some Possible Weaknesses
===
- It will cost less than a nation-state of energy to reverse recent Bitcoin transactions.
- Some miners may protest and lobby exchanges.
- By pushing mining towards the cheapest energy sources, centralization increases towards Chinese miners.
- The Bitcoin network may split if consensus is not built before flag day.

However, given the current political headwinds and widespread public discussion around Bitcoin's energy use, it may be socially possible to ask individual users and major exchanges to install a version of Bitcoin with a reduced block reward.

Alternatives
===
Instead of outright rejecting transactions (and the blocks that contain them) that attempt to spend increased block rewards, treat them as no-ops.
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