[InclinedPlane]

Pretty similar to the environmental impact of jumbo jets. A 777-200LR burns around 145.5 tonnes of jet fuel to transport around 300 people 15,800 km. That's 31 grams of fuel per passenger-km, about 86% of the fuel is Carbon so that's roughly 27 grams of Carbon emissions per passenger-km. A BFR/BFS contains about 3,240 tonnes of propellant and allegedly will be able to transport around 850 passengers up to 20,000 km. The oxidizer to fuel ratio of the Raptor engine is currently unknown but it's likely it's around 3:1, meaning that 1/4 of the total propellant is Methane while 3/4 is liquid Oxygen, giving 810 of Methane per trip, give or take. Methane is 75% Carbon so a BFR flight should produce roughly 608 tonnes of Carbon emissions, or 36 grams per passenger-km (30% more than a conventional flight, seemingly).

However, it's possible to generate Methane fairly easily using solar power, so such launches have the potential to be nominally carbon neutral with some investment.