In this article about Ethereum Metropolis one feature of this next stage they discuss is using proof of stake instead of proof of work to create new coins 1% of the time.
They list a few benefits, but one thing jumped out to the environmentalist in me. This quote -
The world’s bitcoin miners spend around $50,000 per hour on electricity. That’s $1.2 million per day, $36 million per month and ~$450 million per year! Just put your head around those numbers and the amount of power being wasted. By using “Proof-of-stake” you are the making the whole process completely virtual and cutting off all these costs.
When Bitcoin started I dismissed it as being another way to turn fossil fuels into money, because I'd don't understand that proof of work wasn't the only way to do blockchain. This change could make a big impact on the carbon footprint of the blockchain.
BTW The post has a good explanation what proof of work and proof of state work and function. Also, it makes a case that this switch to the next stage of Ethereum could lead to a rise in value and decrease in the contribution of Ethereum to global warming.