The first and second stages of a Falcon 9 use a combined ~163 000 litres (43 000 gallons) of RP-1 fuel. This is less than the fuel capacity of a Boeing 777-300ER.

So if the Starlink launches happen twice a month, the carbon footprint from the fuel would be at least an order of magnitude smaller than that of a single long haul route of an airline.

Building the satellites and the rocket (including the expendable second stage) is obviously pretty carbon intensive too, but fuel is probably what you were thinking about when posing this question.