[pmayrgundter]

Interesting point!

It looks like Skanska is GC for the Project, and cites it as a 9 acre (!) lumber roofing system[SK], and that it uses 3.5M board foot of Douglas Fir Project Lumber[PL].

Douglas Fir is 3.2 pounds per board foot, or 1.45kg [DFM]. So 1.45 * 3.5M = 5Mkg of lumber for PDX airport.

DF has an Embodied CO2 of 1.6kgCO2/kgLumber [DFC]. A little hard to believe? But maybe that's bc a lot of the mass of a tree is left in the ground. Worth following up.

1.6kgCO2/kgLumber * 5MkgLumber = 8MkgCO2 = 8KtCO2 embodiment/sequestration from the PDX roof project. (tho there's a lot more to the project that probably goes in the other direction)

Global CO2 emissions from commercial flights is ~60MtCO2/month [CF], so we need roughly 12,000 airports per month, 144,000/yr, to offset flight CO2 emissions.

There's 9000 commercial airline airports [NA] (tho obv many smaller than PDX, but they would also represent less CO2 from their flights), so 144,000/9000 is a 16x annual airport rebuild rate we'd need to offset CO2 emissions from the flights they service.

So yeah, this is absurd on the face of it.

But, how much of the mass of an airport is the roof? If it's like 1/100th the total mass, and you start building airports with all wood (foundation, runways, etc) you'd get to 16% annual rebuild rate to offset flight emissions. Still too high to be plausible. But another 10x somehow and you get to ~1% range of annual airport rebuild rate to offset emissions.

Then you'd have something.

[SK] https://www.usa.skanska.com/what-we-deliver/projects/278172/...

[PL] https://www.forbes.com/sites/johnoseid/2024/08/19/portlands-...

[DFM] https://www.globalwood.org/tech/tech_wood_weights.htm

[DFC] https://www.douglasfir.co.nz/net/environment/carbon-footprin...

[CF] https://www.statista.com/statistics/1500409/global-aviation-...

[NA] https://sentinel-aviation.com/blog/over-40000-airports-in-th...

[pmayrgundter]

Based on the discussion in the descendent thread with morsch, it seems like the runways are the real story, at 1000x the mass of the airport roof.

But concrete is not so CO2 intensive. Lumber has a +1.6 sequestration factor of CO2 emitted vs built mass, compared with concrete at -0.8.

So we'd need runways made mostly of wood, or combined with a Woodcrete that was net sequestering, and then maybe there's a way to make even our most CO2 intensive industries net neutral so long as we rebuild continuously.

Also, since construction is about 40% of global CO2 emissions, if it could become a net sequestration as a whole, maybe it could flip the sign to -40% and offset most of the rest of our industrial emissions.

This also got me interested in what's a good number for rebuild rate.

Found a study that concludes the "Apparent ecosystem carbon turnover time [T]" is 43±7 years.

So maybe we should be rebuilding our built environment at 2.3%, or probably higher since species have evolved to be more energy intensive, humans especially.

[T] https://essd.copernicus.org/articles/12/2517/2020/essd-12-25...

[morsch]

> tho there's a lot more to the project that probably goes in the other direction

I mean, this is obviously why this is just a fun math exercise and not much else. Building an airport, even if you build part of it out of wood, is not net carbon-negative.

[pmayrgundter]

Just finished the full edit.. check it out. If the full airport is made out of wood, seems like it's getting towards plausible, or at least not obviously wrong

Most uncertainty is how much mass the ceiling is compared to rest of airport. Maybe it's more like 1/10th. Hmm