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.
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.
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.
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.
See my comment here: https://news.ycombinator.com/item?id=31930716
I suppose walking in a foreign city is not accounted because agricultural production, transport, hospitality etc. already is accounted elsewhere.
There's surely a need to join up all the accounting up though.
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.
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.
[1] https://pubmed.ncbi.nlm.nih.gov/9309638/
[2] https://nutritionj.biomedcentral.com/articles/10.1186/s12937...