Apologies for my very late comment. I'm hoping it still might help someone.

I had the exact same question a few years ago. Not really knowing where to look I ended up going to AngelList to search through the job openings with the tag 'cleantech'.

That's how I ended up at Sunfunder (http://sunfunder.com/). We finance renewable energy in Africa, India and other places that can definitely use a clean alternative to either kerosine/diesel or no electricity at all.

Honestly, I can no longer imagine not working somewhere where I don't contribute to the cause (although I wouldn't mind working in healthcare of something similar impactful either). It makes such a difference in my personal well being.

It might be worth noting that wanting to contribute with our software skillset means you will quite likely find a job where you support others of your team, instead of building the main product yourself. There are of course many exceptions, but most companies I found that were contributing to the cause were not software-first companies.

For me this was a welcome change, and I find it much more gratifying to use my skills to make internal processes work smoother and to support my colleagues than to be making the flagship product in a software-focused company. Your focus shifts from high-tech knowledge building to trying and figure out how to support the business, preferably with the most simple tech solution you can come up with. It might not be for everyone, but I personally love it.

Besides Angellist I imagine you can find some inspiration on Idealist.org. It might even be worth browsing through the "Who's Hiring" thread on HN for any companies in the 'contributing space'.

I also have a personal list of bookmarks I keep with companies that might be worth working for, impact wise. Feel free to e-mail me and I'll send them through.

If you're from Belgium or Netherlands I actually made a site myself for job openings specific in renewables/health care/other impactful stuff, http://joppo.org/. It's so obviously a work in progress that it's embarrassing to share it, but it might be useful to fellow BE/NL peeps.

Feel free to contact me any time if I can help out.

Industrial agriculture is often under-represented in these discussions, but it's the leading or second-leading cause of climate change. At the same time, diet-related disease is the leading cause of human death. Growing some part of your diet is a really important thing that people need to be doing.

So you could get into growing some food or look for ways to support local farming. To those points, my startup project (terrafarm.io) is a web platform for making it easier for people to contribute to local food systems. It is only a demo atm, but the plan is to have an official product this upcoming Spring. I'm the only person working on it full-time, but I'm always on the look-out for people who care about the problem and want to contribute. So far, I've only hired contractors because I can't afford more than that. But feel free to PM me if you have any interest or feedback on the concept.

I see two critical areas for contribution: tools for emotional persuasion and tools for collective planning.

it's not a naive question, it's what's on a lot of people's minds, including mine..:)