It depends mainly on distance travelled. Including non-CO2 effects such as contrails, which roughly double the impact of CO2 alone, a return journey from Paris represents around 0.16 tCO2e for London, 0.4 tCO2e for Barcelona, 2 tCO2e for New York, 3.8 tCO2e for Singapore and 6 tCO2e for Sydney. These values use ADEME Base Empreinte emission factors (225 gCO2e per passenger-km for short-haul, 178 gCO2e for long-haul). For comparison, the same Paris-London journey by Eurostar emits around 0.01 tCO2e, more than 10 times less.
Read the source article: Flight carbon footprint: the figures by destination