Why do those mathematical arguments about CO2 emitted never include how much CO2 would be emitted by a person (and transitively emitted, too - i.e. how much CO2 would be required to produce the required food for the person) if they did the job themselves?
I.e. somehow walking 100 steps suddenly produces 0 CO2. Which is completely not true, at least in this case the person would be breathing, let alone spending calories walking up the stairs.
Because humans, trees, living things in general are carbon neutral over a pretty short duration.
The overwhelming concern is carbon that was newly put into the atmosphere from fossil fuel sources comprising millions of years' worth being released all at once (less than 200 years). Carbon that was recently removed from the atmosphere by plants which were subsequently consumed and reintroduced into the atmosphere is a very minor concern.
It's not that your perspective is wrong, just that it is dwarfed by many orders of magnitude, in respect to fossil fuels.
If instead of flying somewhere I traveled there by foot, I would surely use a lot of energy as well. Not just food and breathing, but also cooking, heating of the BnB I am staying in.
Surely you could say that this would be much less than a typing continental flight on a jet (you are probably right) and at that point the human CO2 can be considered a 0. But what exactly is that 0?
If you assume human produces exactly 0 CO2 all relative comparisons become basically infinities. It's infinitely better to walk than to cycle, it's infinitely better to walk than to fly, etc. But it's not really true. It may be several orders of magnitude better, even - but how many exactly?
I literally never saw this in the research in regards to CO2 produced.
For all of the days that you are alive you need to eat, breath, cook and heat the room that you are living in. The continental flight just allows you to eat, breath, cook, and heat in different city. You cannot account for the carbon cost of the time that you spent travelling, as flying-self will still have a carbon cost sitting around a pool waiting for walking-self to arrive.
>> It may be several orders of magnitude better, even - but how many exactly?
It's not an easy question to answer. I suspect it would be fun to try. Perhaps more for you than for me. But, aside from the pleasure of working this problem, there remains the other problem. And an answer to your question is almost entirely immaterial to that one.
I think the difference between our approaches is that you are focused on relative amounts - how exactly to account? My concern is with absolutes: a metric fuck-tonne is coming from (effectively) nowhere and going into the atmosphere in almost zero time.
It'll surely be more efficient to account for the future emission at the point of fossil extraction, with special consideration for reliable CCS.
For example, imagine that I am taking an intercontinental flight in 8 hours:
- I spend 8 hours flying from London to Mumbai. The majority of my CO2 emissions come from the plane jet engines.
- I spend a month walking between London and Mumbai. The majority of my CO2 emissions come from the food I consume.
Note if I DID fly I would not have spent that 1 month eating, BNBing, using Air Con for a month. Which means that is the CO2 cost of my month-length walk.
Honestly, I started working this out because I thought it would be negligible. But I think you're right to doubt. Leaving aside the question of how much a human produces, since two people have suggested human output is neutral and I don't know enough to question it:
It takes an average of 0.10kcal to walk up/down a step, averaged.[1]
2.2kg of CO2 are emitted per 2000kcal of consumption (I just averaged table 3 for want of a better idea)[2]
37 steps in a staircase (TFA, 46 total - 9 flat)
3.7kcal burned, 3.7kcal * 1.1g/kcal ~= 4g CO2 per person per trip
Obviously very rough, but unless I've made an order-of-magnitude error it's in the same ballpark.
Does that mean that if I eat meat it may be more beneficial to travel by car because a vegetarian is 1000 times more efficient than a car vs a non-vegetarian who is only 200 times more efficient than a car? (numbers are made-up)
I.e. somehow walking 100 steps suddenly produces 0 CO2. Which is completely not true, at least in this case the person would be breathing, let alone spending calories walking up the stairs.