As bitcoin can be mined anywhere the incentive structure is to find unwanted lowest cost energy sources so the numbers may be less dramatic in that context (Flared natural gas, hydro overflow, solar and wind curtailing). Bitcoin is new technology so people think of this energy expenditure as 'wasted' it is in fact securing the bitcoin blockchain. This is as valuable as the market dictates. Many people see this decentralised settlement as something worth having just as you might look at a bank or a gold mine or the SWIFT system and don't automatically think that its a waste of resources. If you think this is a waste of energy chances are you have not bought into the benifits and use cases associated with a bitcoin settled financial system. As civilisation progresses we use more and more energy and markets decide what people deem a useful purpose for this energy.

For sustainability I think there are two major factors to consider

1. Base layer Vs Secondary layers

- Extrapolating out the transactions and energy use doesnt work because more efficient, cheaper layers with more utility will be built ontop of the base layer. This allows for a framework for small transactions to sit on a final settlement layer. Therefore knowing the future energy consumption of the network is very hard.

- It is not really known how much security is optimal for the network at the moment more is considered better

2. Source of energy

- Ideally green energy. This is a political issue that requires policy to incentivise change to green energy generation. Ask yourself if this criticism holds up if we had abundant almost free renewable energy. Already many grids are considering paying people to use excess solar and it increases every year.