Ash Realistically, is there a lot people can do to improve the environmental/energy impact of BTC?
No, not really, apart from not using it.
The first problem is that it is always going to be 'mined' in the places that are cheapest to do that, and they are at least at the moment mostly getting all of their power from coal fuelled power stations.
Apart from where it is being mined, the problem is that Bitcoin is just hugely energy intensive compared to all of the more modern cryptocurrencies, but at this point it's not possible to change that.
This is a list of some cryptocurrencies and the amount of energy they use per transaction in Kilowatt hours (KWh)
So, Bitcoin is using 11 times more energy than Ethereum which is already using a lot more than most of the others!
If a nation really feels the need to make a cryptocurrency a national currency then some of the others available, i.e. Ethereum are as mature and stable as Bitcoin, with a fraction of the energy footprint.