Also, this site has a growing list of practical things we can do:
Upcoming challenges, for example, are grid balancing with the increasing amount of constantly changing renewable energy input, maybe to coordinate load on the grid with it (eg only start washing machines during the day when solar is available). Predicting near-future inputs from wind and sun forecast models also plays into this.
You can also always work on making things more energy-efficient or optimize processes so less energy is used (Manufacturing for example uses so much transport for in-between steps. Can we get rid of some of them?).
The holy grail is probably carbon capture. Some people are also working on that and might be able to use your expertise.
Another topic is mitigation. Enabling people especially in poorer countries to withstand increasingly frequent disturbances better - resilience - will help greatly. Many non-profits who work on this would love to have you help with technology. They can also connect you to ongoing state projects I think.
And then there is climate modelling. Some efforts are made to make the models accessible to the public, but it is hard. If someone put some work into this that would help a lot. Additionally, scientists are not the best coders. The best are working on the models, but in general the coding practices are severely lacking. You might be able to come around and just teach about that, and learn which kind of tools would be helpful. But then we know all we need to act at that front.
Do you have a list of places where scientists are inviting coders to come and talk to them about coding practices? (Or organizations that can help with this)
What are some non-profits who work on enabling people in poorer countries to withstand disturbances? Are they looking for coders?
Who is working on carbon capture and looking for volunteer collaborators?
The International Research Institute on Climate and Society at Columbia University's Earth Institute is looking for a programmer to work on their Data Library. Unfortunately I don't see a way to get a permalink to the job listing; you can find it by going to https://jobs.columbia.edu/ , clicking "SEARCH OPEN POSITIONS" in the left nav, and specifying Department 6061.
I'm not affiliated with the group. I actually interviewed for the position last week, but probably won't end up taking it.
I can tell you that every DOE lab has scientists and programmers working together. In fact, the two largest super computers, Summit and Sierra, are GPU based, and there's a huge decrease in power consumption. For example: Summit (#1) has ~7.5x the power of Titan (#9, and at the same facility: ORNL) but only uses ~20% more electricity (Summit and Sierra are GPU based)[0]. Aurora, the planned exascale machine, will be 5x Summit and only use 20MW (~2x power) (actually that's the number that's the hard upper limit). That's a big deal. And a bunch of teams there are working on making everything more efficient and how to better utilize resources.