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Biosphere 2 – The Why Is Important



That things go wrong is just part of the human condition – best laid plans of mice and men gang aft algey and all that. Although presumably that means it applies to the murid life condition as well. The thing being as those sometime intelligent beings, humans, we need to work out why something went wrong. The illuimination this knowledge provides can be rather helpful elsewhere – widen the area that we can go look for our keys when drunk for example.

So it is with Biosphere 2. A nice report on it is here. The problem though is that it mentions the major technical problem they had but doesn’t explain why. That why being rather important and something that illuminates a much larger are between the lampposts, how we deal with climate change. Or even something we don’t have to worry about so much as we do deal with climate change. That being cement.

The grand technical problem Biosphere 2 had – as opposed to the social one of 8 people perhaps not being a large enough group of humans to get along with each other for 2 years – was the oxygen levels inside:

On top of that, oxygen levels decreased faster than anticipated, with a corresponding build-up of carbon dioxide. Earth’s atmosphere is about 21% oxygen, but inside the biosphere it fell to 14.2 %. “It felt like mountain-climbing,” Nelson recalls. “Some of the crew started getting sleep apnoea. I noticed I couldn’t finish a long sentence without stopping and taking a breath of air. We worked in a kind of slow-motion dance, with no energy wasted. If the oxygen levels had dropped any lower, there could have been serious health issues.”

Well, where was all that oxygen going? To understand,m the chemistry of cement. Portland stone, what we make cement from, is essentially calcium carbonate, CaCO3. We make the cement by heating it to drive off the CO2 and have CaO – it is left to the reader as an exercise to check whether it’s actually CaO2 or not. We then mix the CaO with water plus possibly sand and so on to make concrete. As it matures it sucks back in that CO2 and sets back into being stone.

Yes, more complex but that’s the nub of it.

So, what happened inside Biosphere 2? They built it, then sealed it, adding oxygen, but without including in their calculations how much CO2 was going to be absorbed by that maturing cement/concrete. Which is where their O2 disappeared to. This was solved, eventually, by adding oxygen to replace that now in the fabric of the building.

The larger lesson of this. We’re told, righteously, that cement manufacture is some 6% (others say 8%) of carbon emissions in our current world. The process of making the stuff is the driving off of CO2 into the atmosphere. Some say this means we’ve got to solve – ie, not have – cement to deal with climate change. This not actually being so for the reason above. The concrete buildings absorb the CO2 as they set. Our calculations of the CO2 effect of cement are including the release from manufacturing and not the collection from the atmosphere of maturing concrete.

Cement provides a bolus of CO2 not a permanent addition of it that is. It’s still perhaps something we should think about but it isn’t the problem the current calculations say it is.

Why something happens is important to understand for the knowledge gained by this one problem over here can illuminate the solution to this other one over there.

Cement just isn’t the problem current climate change science tells us it is.



  1. So you’re telling me that CO2 emissions during cement manufacture are a fraction of a per cent of total CO2 emissions, and the cement itself sequesters most of that by itself in curing. The nett flux as a per cent of total emissions is indistinguishable from zero. Right. If your calculator has enough decimal places, let’s talk about cow farts.

  2. Why is this news? I remember reading about this in the 1990s.

    (I tried to comment last week when you first posted, but it didn’t work.)


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