[arandr0x]

Public transit systems do have need of programs for control, infrastructure maintenance and so on, as do railroads.

There's (some) work in conservation (meaning ecological habitats and stuff) if you care about biodiversity, but it mostly requires GIS skills.

A lot of "global problems" (like cancer) are also local problems (like different environmental exposures or individual genetic profiles). It's hard even while working at a global problem to have a solution with global impact. This cannot be understated.

There are some decently big problems in mining (where mining certain compounds has become exponentially harder) and the industry does not typically have a lot of software talent already. However, it can be quite difficult to get into depending on your geographical location.

Have you considered working for the government?