Not to disagree, but the bigger factor for environmental gains is likely backend languages. If people could stop writing servers in languages that are literally 40 times slower (Python with Django, Ruby on Rails, etc.) in terms of the number of requests it can handle / throughput, that directly translates to more server instances behind a load balancer, which translates to 10 times the electricity usage.
That, imo, is totally unacceptable (also, financially not optimal).
I've had people tell me that the "developer productivity gains" of using Python totally justifies the circa 10 X electricity usage + 10 X hosting/cloud costs. (Yes, developers cost a lot, but the hypothesis that Python/other slow languages result in so much higher developer productivity is a questionable assertion -- especially, in contrast to languages like Kotlin, Go, etc.)
Are you sure that servers are really a bigger factor? Sure, it's easier to see how much power a data center consume but there are literally billions of client devices out there.
At least with backend software there is a financial incentive for efficient software. For client software there is no incentive unless there is actual competition, of which there is often effectively none as in the user cannot choose better software because interopability is not a thing.
That, imo, is totally unacceptable (also, financially not optimal).
I've had people tell me that the "developer productivity gains" of using Python totally justifies the circa 10 X electricity usage + 10 X hosting/cloud costs. (Yes, developers cost a lot, but the hypothesis that Python/other slow languages result in so much higher developer productivity is a questionable assertion -- especially, in contrast to languages like Kotlin, Go, etc.)