Or said in another way, does packing lighter on a trip actually make a dent in one's co2 emissions?

According to The carbon independent site,

CO2 emissions from aviation fuel are 3.15 grams per gram of fuel [38] , which gives CO2 emissions from a Boeing 737-400 of 115 g per passenger km.

What it does not talk about, however, is the weight of the passengers and their luggage. Any write-ups on that?

What are the average per-passenger-kilogram carbon emissions of common commercial passenger aircraft per kilometer?

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    $\begingroup$ There are so many"it depends" variables that any answer here is almost meaningless. Full aircraft, or half full? Short hop, or long haul? Old aircraft (like the 737-400 mentioned), or more modern? Flying a "least fuel" (slow) profile, a min time (more fuel burn) profile, or something in between? VTC as unanswerably broad. $\endgroup$ – Ralph J Jan 25 '20 at 21:49
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    $\begingroup$ If you care enough about this to worry about nickel and dime numbers like that, why are you traveling at all? $\endgroup$ – John K Jan 25 '20 at 22:04
  • $\begingroup$ You may restrict your question to a specific aircraft type (e.g. an embraer E-jet) and a specific route (to have a taxi, climbing, cruising and descent time) $\endgroup$ – Manu H Jan 26 '20 at 8:53
  • $\begingroup$ @Therac yes thanks! So about 1/20kg co2 per kg luggage per flight hour for an A320! $\endgroup$ – user46366 Jan 26 '20 at 14:15
  • $\begingroup$ @begs-the-hessian Approximately 40-50 grams fuel and correspondingly 130-150 grams CO2 per hour flight per kg payload. This will hold approximately across various aircraft types (the A320 takes a bit less fuel than average due to being short-range and modern). $\endgroup$ – Therac Jan 26 '20 at 15:23