While time-limiting the mining process could be a potential solution, the real goal is to gather ideas from the community on how we can effectively address these criticisms. If there are alternative suggestions on how to address the major concerns surrounding bitcoin, we'd be happy to explore those as well. This post is just a starting point for brainstorming, not a final proposal.
The answer to this lies in your original post:
Global warming is one of the key issues facing humanity in the 21st century. Research has shown that 67% of the electricity used for bitcoin mining in 2020-2021 came from fossil fuels.
That is to say, the answer lies in further shifting towards renewable energy. If 33% of electricity being used for Bitcoin mining is renewable, it's actually ahead of the curve, with renewables consisting of only 28% of global energy production in 2021:
https://en.wikipedia.org/wiki/List_of_countries_by_renewable_electricity_productionIf Bitcoin spearheads renewable energy and helps building infrastructure for renewable energy by providing additional economic incentive, everybody wins.
This might not be easy, but unlike creating trustless hardware for some convulated "Proof of Idle" it would be
possible. And it would have a tangible positive impact that goes beyond the Bitcoin mining business.