Yes, I agree the CO2 output is minimal but we should I think look for greener solutions now? Solar has come down drastically in price in the last decade.All natural gas lines in the US are underground, just like water. Power (and phone and cable) in older neighborhoods is above ground poles. Newer neighborhoods have gone to underground utilities.
I'm pretty sure it's natural gas/propane fired motor. As for generating CO2, for emergency purpose, kicking into gear every year or two for a few hours or days, I think the carbon footprint would be minimal. It doesn't run all the time. They pull power from the grid, just like you and I.
I know of 2 people who have installed Generac home generators. They were costly, at about $7-8000 installed, but they don't worry about power outages. No lost food, frozen pipes or flooded basements from dead sump pumps. No fear of ice storms in January. If you have the money, it's peace of mind.
With regard to generators, several years ago a farmer here invented a system whereby his juice was supplied initially by batteries and an inverter and only if/when the battery voltage dropped to a critical level did his generator kick in. Thus he saved a lot of fuel for short term outages. In these days of processor control such a package should be beer into water to implement?
Dave.