There are many ways you can start “accounting” for CO2 (as comments on the previous article also showed), but at the end of the day what matters are absolute CO2 emissions, from whatever activity. And cutting down a tree and using it as a column (or a table, or a ladle) has no negative or positive effect (now). (Apart from possible embodied energy, but that’s another story) That was the thrust of the first part, a somewhat clinical reasoning based on 1 example, and for the sake of convenience assuming some fixed values, a static calculation.
But actually it is a dynamic process, in which land and time are important factors: in the reasoning the regrowth of 1 tree has been taken for granted, and in that example it takes 50 years. It is indeed 1 tree, but then it is not just about that tree, because that tree also takes up space, or land, say 25 m2 , then you have to secure that 25 m2 of land for 50 years and more. You can compensate the raw material faster, and thus create CO2 bonding faster, but then you have to commit a larger (land) area: with two trees it could be done in 25 years*. But then you have to dedicate twice as much land, or 50 m2, for a that time.
I like to use the island example: imagine you arrive on a small uninhabited island of 25m2 , and there is 1 tree. From that wood you build a hut. Only one tree can grow there (25 m2), and you have to wait 50 years for it to grow back, for the wood stock to return to its former level, and for an additional amount of CO2 to be fixed in the same amount as was bonded in the wooden hut and had been bonded already before that in the tree … In this particular case, of course, that tree is ‘insured’, it is on that same island. You can then cut down that tree again at t=50, and use it, say for a fishing boat, and the process starts all over again, though at a higher fixed CO2 level. But it will take another 50 years before the next amount of CO2 is fixed. If you want to speed up that process, you can, but then you need a bigger island…. An island of 50 m2 for example, with 1 tree at t=0. Then at t=0 you cut down that one tree, and you plant 1 more to grow 2. Then after 25 years , t=25, the wood supply has been restored, and the CO2 sequestered, 2x as fast, but also 2x larger land use…. The land per unit of time take remains the same. And remember, the earth is also an island….
And yes. it can also be done in 1 year, but with 50 times more land use. Then after 1 year there is as much CO2 sequestered as was bonded by the wood in that house. And you can use the new wood again. But calculated over 50 years it makes no difference, per home. At least, that first house still has to last a long time, say 50 years, and longer, otherwise the effect is negligible… If that first house decays or burns earlier, then there is no CO2 effect within that time, and then subsequent harvests have to be invested in rebuilding, so we still don’t make any progress. Not to mention investing embodied energy over and over again. (With also a land-time relation…)
So, in fact, the only good way to calculate is in land-time, which is the mechanism that regulates both wood and CO2**. And that is a fixed quantity, the amount of land ( per country or globally) is limited, and time cannot be accelerated or slowed down.
I did initially calculate with 50 years for homes, for convenience, that is, the idea is that someone independently occupies a home for about 50 years. (Although with increasing life expectancy you should now make that 60). And that someone is only once occupying land and time for his own housing. If the house has a shorter lifespan, then someone’s personal land-use claim quickly increases. And if the house lasts longer, the community benefits, because there is a house available without material investment (apart from maintenance). The longer that home lasts, the better, therefore. As I concluded my book: if every generation had to build its own built environment, progress would be impossible. [1]
The wood example applies equally to shorter rotation crops, which also store CO2. Basically the same reasoning: you can use short rotation crops , but that too is a land time relationship. Suppose you need the harvest of 1 hectare for a hut made of straw bales, then 1 year later that stock has been recovered, and CO2 has actually been fixed in the amount that was also in the original stand (and now in the hut). t = not 50, but 1 year, but with 1 hectare-year of occupied land! For example, if you have only 400 m2 available, you need the harvests of 25 years before you can build the same hut (again).
This does not alter the fact that in all cases no CO2 is fixed at the first use. After that it is in fact a land-time relationship per function: fast and a lot of land, or slow and with little land. So for both the raw material and CO2 storage there is a land-time relationship!
Calculating over 1 building is, when it comes to CO2 and raw material stock, not that relevant. As a relative comparison of buildings ok, but not for absolute effects. As argued, you have to consider the raw material chain as well as the CO2 chain,[2] which are land and time bound.[3] These can only be used once at a time, so it is best to look at the total land-time availability to see what is best to realize with the available potential: in a manner of speaking: 1 large house or several smaller houses.
This also applies to minerals and metals, which are also renewable! Albeit on very long time-land scales, but that is not yet a generally accepted approach. I have been writing about this for years, and recently the ‘Conscious Land Use Foundation’ published a beautiful brochure explaining this: “Maintainable Land Use’ . (See the brochure here [3] and the background here [4])
What is possible, though a bit more complex, is to calculate over the entire (building) stock: as long as you do it within a given amount of land. Like for example the Netherlands ( as the ‘island’). Then within those boundaries you can both realistically manage the raw material chain, as well as the absolute cumulative CO2 emissions and storage, in relation to buildings, with land in that case as a fixed quantity (land surface of the Netherlands), and then only time is relevant, in relation to building volume. And then again: everything related to maximum CO2 budget. Since we are not in balanced situation, where you can spread every impact over time, but in a situation that we have to decrease fast, to avoid huge problems.
(All this of course assuming the land has not been sacrificed to golf courses…[5] )
* Assumed as an example, in reality CO2 storage is not linear with tree growth, so it is questionable whether two trees after 25 years contain as much raw material or CO2 as 1 tree after 50 years.
** The ocean also absorbs CO2. We will leave that out of consideration here, but it can also be included as a ‘land’ cq surface and time relationship.
[1] People vs Resource, restoring a world out of balance, publ. Eburon, isbn 9789463012553 , https://www.ribuilt.eu/product/people-vs-resources/
[2] http://www.ronaldrovers.com/half-the-agricultural-land/
[3] https://bewustbodemgebruik.nl/wp-content/uploads/2021/08/Volhoudbaar-landgebruik-BROCHURE-2021-1.pdf ( in dutch)
[4] http://www.ronaldrovers.com/the-renewal-time-of-all-resources-maxergy-3-0/
[5] http://www.ronaldrovers.com/golf-the-decadence-in-our-use-of-space/
