So I just booked two one-way tickets:

A) From Melbourne to Canberra

B) From Canberra to Melbourne.

Both were the same class and category of ticket. As per usual, Qantas asked me to offset my carbon. What caught my attention, however, was that value differed.

On A - from Melbourne to Canberra, the Emissions Offset (C02-e) was for 93kg at AUD$0.86.

On B - from Canberra back to Melbourne, it was for 104kg, at a charge of AUD$0.97.

Why the difference for the same distance?

  • @Flimzy I have no idea, but you may be on to something there. If you can find a source, it could make a valid answer.
    – Mark Mayo
    Feb 21, 2014 at 23:07
  • Do the flight times differ? i.e. is it scheduled to take longer to go one way than the other? (Perhaps due to winds, perhaps due to typical airport hold delays)
    – Gagravarr
    Feb 22, 2014 at 10:16

1 Answer 1


I suspect this is a result of Jet streams. This is most commonly observed by different flight times between the same cities. It generally takes longer (25% or so) to fly from Europe to the U.S. than from the U.S. to Europe. This is because the high-altitude jet streams across the Atlantic blow from west to east, providing a boost in one direction, and a penalty in the other.

You can read a bit more about it here, as well as many other places on google.

The jet stream will either improve fuel efficiency and flight time, or hurt it, depending on whether the aircraft is flying with or against the wind.

To help compensate for jet streams, routes are often altered one way or the other, to provide for the most efficient travel. This can lead to drastically different miles flown, as well. On aircraft equipped with flight status monitors, you may notice the discrepancy between two flights. Unfortunately, I doubt this will ever affect your frequent flier miles :)

This would easily explain a difference in carbon emissions.

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