What I specifically handle is Water. Starting from the natural system (weather generator + Hydrology) through to the human system (Demand model (showing increase over time and temperature increase) + system operations (dams, reservoirs, treatment facilities, pipes, etc.) to delivery to customers.

The big problem we answer is "How can we continue delivering water to people while under climate change uncertainty? What policies or new infrastructure can we build so we remain robust and resilient under these new conditions?"

I would guess something like transport (train network) or maybe utilities (power grid)?