Loose estimate based on preliminary data for BFR:
BFR first stage gross weight is 4400 tons (IAC presentation 2017). If I set the mass fraction to 90% that's 4000 tons of methane + LOX. The second stage has another 1100 tons.
Assuming all of that is burned on a flight (worst case).
The reaction is CH4 + 2 O2 = CO2 + 2 H2O, ratio 42:36, is 2746 tons of CO2.
Payload to LEO is 150 tons, that's (my estimate) enough to carry 800 passengers.
For comparison, a Boeing 747-400 uses 60 tons of fuel for a 5500 km long flight carrying 400 passengers, producing 189 tons of CO2.
So for a transatlantic flight, a BFR produces 7x as much CO2 as an airliner. For the longest flights (London-Australia, 20,000 km), fuel consumption of the Boeing increases by 4x.
I already assumed the BFR consumes its entire tank capacity above, so for this flight the BFR produces 1.4x as much CO2 as an airliner.