I was referencing directly the amount of compilation, not necessarily the power consumption. But with regards to ecological impact, I would guess you have Java on a server in your mind.

But, the biggest Java user in term of number of devices is Android. And every time you install an app, you compile it. Including every time you update it (which nowadays is... everyday?). Also it'll recompile in background to use pgo. Nowadays [1] Google could pretty much compile it server-side for most devices, and save a lot of battery wear (batteries wear when getting hot, and compiling, weirdly, heats), in addition to power consumption.

It depends on how you use it. For long running applications like services, yeah, the JIT will get the bytecode down to some very high quality machine code. If you write lots of small applications and compose them using something like Unix, then Java is very inefficient.

Well, even if everyone did have heat pumps, let's think about it a bit. I upgrade my system about once a week. I reckon on average it's about 1 hour of compiling per week but let's say 2 to be safe. That's no more than 1 kWh per week. A fridge-freezer will use that in a day. An electric oven will use that in 15 minutes. An electric car will use that travelling 3-4 miles. Most households use something like 30 kWh per day to heat. Even if a heat pump made that like 10 kWh it's still a drop in the ocean. And don't forget the resulting binaries run slightly more efficiently because they are compiled specifically for my CPU, plus I enjoy it.