Brendan, I'm a big fan of your book, and work.
I don't have a problem with you joining OpenAI; best of luck there!
However, I'm not sure your analysis is quite correct, in this case.
If OpenAI can mobilize X (giga)dollars to buy Y amounts of energy, your work there will not reduce X or Y, it will simply help them produce more "tokens" (or whatever "unit of AI") for a given amount of energy.
So in a sense you're helping make OpenAI tools better, more effective, but it's not helping reduce resource usage.