I'm not convinced that tightening up web development practices is what's going to solve climate change, but:

> When you push the CPU processing of the UX from the mobile device back down to the server, the energy consumption certainly moves. Does it decrease, though?

One could argue that developers/website owners might be more motivated to optimize their server code for performance, thereby decreasing their hosting bills, vs optimizing front-end code which they don't pay to run.

You're assumption that it'd move server side is incorrect. It would simply disappear. When you use a javascript library the browser has to process and load all the functions in the library, even the functions that aren't used. This wastes memory and processing cycles on the client computer.

> When you use a javascript library the browser has to process and load all the functions in the library.

That simply isn't true. Your device does load a library (usually minified), and parses the JS to be sure it is runnable. But it doesn't run every function just because it is loaded in memory. Even if it did, it happens on app load, once... then runs functions on-demand. And the size of the load can be mitigated with appropriate use of tree-shakable libraries. But without JS, the server regenerates an entire page, every time you do something, which takes some resources. It sends it over the wires, which takes some small amount of resources. The mobile device loads an entire page again.

I do agree there is wasted processing in both scenarios. But that waste doesn't just disappear when you do server-side work.

Some of it moves server-side anyway. Counterpoint servers require expensive cooling, phones do not.

We all can over approximate in our preferred direction.

surely the more the client can do, the better.

Their machine is already on and idle, by pushing processing onto the backend your just creating a provisioning issue where either under or over provisioning is a waste of people's time or resource.

No. If I want to use an old computer I shouldn't have to wait forever for content because someone thought the client should do the work. That's a bigger waste of my time than your server capacity issues.

If the client device is a desktop computer, sure. Typically, the client is a mobile device whose bandwidth and energy are precious commodities. In these cases, better for the server to do the heavy lifting.