As the total backup solution for a renewable distributed smart grid, how much GHG can biogas help eliminate?  All of it we now produce and even more, to actually reverse climate disaster.

Burning biogas to generate power or using it more efficiently in solid oxide fuel cell/turbines, emits CO2.

The main justification for the CO2 emission from using the biogas is the savings of methane emission from manure run off.   Methane is 21 worse as a GHG than CO2.  That means around 20 times the effective reduction, compared to the CO2 emitted by burning the biogas.

Secondarily, the biogas backs up the grid so it can mainly use wind and solar, GHG-free sources. How much GHG would a renewable distributed smart grid save?  That powers plugin hybrids and geo heat exchange heating/cooling?   Around 2/3rds of the GHG we now produce.

Biogas is an economical well understood storage media as well.  Wrangling with pumped hydro, compressed air, utility scale batteries, or other problematic, expensive systems puts a crimp in the roll out of a distributed renewable smart grid.

Additionally, the organic fertilizer produced as a byproduct replaces the huge GHG releases from fossil fuel and mined fertilizer.  Ammonia is being brought over from Russia on supertankers right now.  That's a huge waste of fuel and huge extra load of GHG.

And it restores dead agrichem soil back to carbon sink activity.  Storing as much CO2 in the soil as is released by using the biogas for electric power.

It's hard to estimate, but I guess about 25 times the GHG released (in actual biogas power generation)is curtailed and sequestered by the entire process of biogas grid backup and organic ag.

It's difficult to imagine any GHG free system that fits together so completely.  And has all it's elements already developed and tested.

This total GHG free power solution even offsets the additional combustion that is still needed for transportation.  A small percentage left for fueling plugin hybrid vehicles and various transport modes not yet amenable to renewable electric power.  Such as aircraft.

But even air travel could someday be plugin hybridized, with better battery technology and solid oxide fuel cell turbofan engines.  It's future technology that has a good chance of working.  Right now in Europe high speed electric trains are replacing a lot of air travel miles.  Those can be powered by renewable electricity.

Of course this would only  happen gradually over the next couple of decades, it's a big change over from our present energy and ag systems.  But it could be in time to really head off climate change if subsidies impell private investment.