I think it's mostly because when they diverged the timeliness back with Shadowrun 1, global warming hadn't been found out about yet.
In game they have fusion reactors, meaning that for electricity they don't need coal, oil or gas powered plants anymore, making things a lot more green. Possibly larger vehicles will use this as well (large cargo ships, sub-orbitals,... just speculating here). Almost all cars are hybrids and in cities if they have gridlink, they drive fully on electricity (from the aforementioned fusion reactors).