The total carbon emissions for a flight from New York, New York to Sydney, New South Wales is 3,722 lbs CO2.
This is equivalent to 1,688 kg CO2e or 1.69 tonnes of carbon dioxide equivalents.
With radiative forcing in effect, the carbon emissions may increase by 2.7 times, so the CO2 equivalents would then be 10,050 pounds, equivalent to 4,558 kilograms or 4.56 metric tonnes.
These calculations are based on the distance from New York, NY to Sydney, Australia which is 9,934 miles or 15,988 kilometers.
This trip is a long haul international flight. The calculation includes an assumption of a 79.7% load factor with 346 seats on the B747-400 and 261 seats on the B767-300ER.