A guy at my local ACX group has very strong opinions on this. He says that there's mainly two groups of people doing studies on the effect of CO2 on human health and cognition: the people who studied its effects in submarines and spaceships, and the people who study mundane indoor air quality. The submarine people are the ones finding no effects at 4000ppm, while the IAQ people are the ones finding effects at very low concentrations. He thinks the IAQ people have terrible study design. He also thinks (iirc) that body effluents (e.g. VOCs) are the real issue, and CO2 is just a proxy. I'll have to forward your post to him next time I see him (a couple weeks?).
As for practically lowering CO2 measurements in the winter, you can just build a heat/energy recovery ventilator, to get fresh air while recovering some of the heat from indoors. My build is 8ft of 6" semirigid aluminum dryer duct, and 2x8ft of 4" semirigid. Join the 4" together with a collar insert thing and tape, put the 4" inside the 6", set up the assembly indoors so that the 6" terminates at your window and the 4" sticks out a foot or two out of the window to prevent short circuiting air, tilt the assembly so that the 6" is tilted down towards the window (.5" per foot?) so that condensate drains out, put an inline fan pumping inwards on the 4" on the inside terminus, and there you go. You now have a ~50% efficient counterflow HRV for $100; the air comes in the 4", exchanges heat with the air going out the 6". I think it should get to 70% efficiency if I bothered to get another 6ft of 6", to increase the exchange surface area. The slower the fan goes, the more efficient it is.
You can also just buy premade HRVs. Get a pair of ceramic Lunos knockoffs from Alibaba for ~$150-200 total, put them in your window, one pointing inward, the other pointing outwards. Or you can get an ERV if you're worried about moisture loss too, that's more expensive though, like $500?
Mildly tempted to make a post about HRVs. I don't think there's a single post on LessWrong about them. But I should finish my post about how I fully treated my non-24 first.
If you don't wanna do that you could do the usual thing of making a Corsi cube/fan (strap MERV 13 filters to box fans) to capture particulates, and then get a huge charcoal bed canister for VOCs (the kind they use for filtering exhaust from marijuana grow tents, like $50-100) and wrap some filter medium around the outside, and put an inline fan on the other end to draw air through it (and preferably put a filter on the other end so you don't breathe charcoal dust). Those huge charcoal filters don't last as long as furnace filters though.
I would be interested in hearing his thoughts and would gladly make a follow up (or add it to my own possible experiment post) if he has convincing arguments that he does not post himself.
I would also read a dedicated post if you made one on how to treat indoor air in a cost effective manner. It is something I am becoming more aware of because of this, one guy on LW posting about ultra violet sterilization, and wanting to get a dog but maintain a clean apartment.
I would do the HRV thing but the deadbeats that run my apartment complex haven't fixed my heat all winter so the absolute max I can get to is like 60 degrees sometimes so I don't have any to spare. That does sound useful and fun to build though.
1I am surprised about the existence of the studies claiming cognitive improvement with 100% oxygen. I had a vague memory that this was unhealthy, and from a little googling I came across https://iere.org/what-would-happen-if-we-breathe-100-oxygen-all-the-time/ which send in line with what I remembered. I did not do any checking for accuracy, but you might want to look into oxygen toxicity before you try anything drastic.
That is an excellent warning and I will certainly not do anything crazy. I got SCUBA certified and do vaguely remember learning about oxygen toxicity so it is something to be aware of, although I'm hazy on the details too. Although iirc early astronauts had 100% oxygen atmosphere but at only 20% atmospheric pressure giving the same partial pressure. I don't think that is the best way to go about this, especially as I think it caused a really horrible fire, but oxygen enrichment is possible to do without toxicity. Still really skeptical of a 30% increase in learning on any task.
Having read a few studies myself I got a CO2 monitor (from AirThings, also monitors VOCs, temperature, humidity etc). From which I can confirm that CO2 builds to quite high levels in an unventilated room within an hour or two. But even leaving a window only slightly ajar helps a lot.
Apparently fan heating and air conditioning systems may or may not mix in air from outside - many just recirculate the same air - so switching these on may or may not help with ventilation.
Some studies suggest high CO2 also harms sleep - though again the research is inadequate. If so, sleeping with the window slightly open should help; if cold/noise makes this impractical, sleep with the bedroom door ajar (if there aren’t other people around) and a window open in another room Or even if no window is open at all, having your bedroom door ajar seems to help by letting the CO2 out. I’ve done this for the last year, though can’t be sure if it’s helped my sleep.
A confounding factor is that it’s best to sleep in a cool room, which opening a window also achieves. Either way this is an argument for opening a window while you sleep.
1In breathwork, there's holotropic breathing where people try to achieve LSD-like states by hyperventilating. While LSD-like states are beneficial for some cognitive tasks, they are not beneficial for most of the tasks we care about for daily productivity and probably detrimental for them.
ChatGPT suggests that low blood CO2 leads to respiratory alkalosis. Blood ph goes up. You get cerebral vasoconstriction, lower intracranial pressure. Hemoglobin binds to oxygen more strongly, leading to tissues getting less oxygen. There are some processes like the kidneys dumping bicarbonate to get the ph down again.
Besides that, you have CO2 receptors that get less activity which will reduce breathing rate and have a bunch of different physiologically effect on different tissue.
If I do this, I’m not buying the parts until I confirm nobody leaves a comment just demolishing the central thesis, I would probably wait until spring as opening my windows seems like a big important step to having low ambient CO2[7] but would be pretty miserable for me while there’s still snow outside.
In Sweden a common setup is called FTX, a balanced supply-and-exhaust system with heat recovery, that exchanges air with the outside without needing to open windows. Swedish regulation set a minimum outdoor-air flow roughly 0.35 L per second per square meter of floor area.
If you do care about reducing CO2 indoors, that kind of technology is likely what you want, maybe with an execution that above their government mandated minimums.
The problem
You are routinely exposed to CO2 concentrations an order of magnitude higher than your ancestors. You are almost constantly exposed to concentrations two times higher. Part of this is due to the baseline increase in atmospheric CO2 from fossil fuel use, but much more of it is due to spending a lot of time in poorly ventilated indoor environments. These elevated levels are associated with a decline in cognitive performance in a variety of studies. I had first heard all of this years ago when I came across this video which is fun to watch but, as I’ll argue, presents a one sided view of the issue[1].
This level of exposure is probably fine for both short and long term effects but essentially everyone alive today has not experienced pre industrial levels of CO2 which might be making everyone very slightly dumber. I don’t think this is super likely and if it happening it is a small effect. But, it is also the kind of thing I would like to be ambiently aware of and I am kind of disappointed in the lack of clarity in the academic literature. Some studies claim extremely deleterious effects from moderate increases in CO2[2], some claim essentially none even with 4000ppm[3], ten times the atmospheric concentration.
A lot of the standard criticisms of this kind of thing apply, underpowered studies, methodological flaws for measuring cognitive performance or controlling CO2 concentration, unrepresentative populations[4], and p-hacking via tons of different metrics for cognitive performance. All of this makes even meta analysis a little unclear. This blog post covers a meta analysis pretty well and the conclusion was that there is a statistically significant decreases in performance on a Strategic Management Simulation (SMS) but that was comparing <1500ppm to <3000ppm which is a really wide range and kind of arbitrary. However, nobody has done the experiment I think would be most interesting. That being a trial where subjects are given custom mixes with 0ppm, 400ppm, and 800+ppm. This would answer not only if people are losing ability from poorly ventilated space but also if we are missing out on some brain power if we had no CO2 in the air we breathe in. Again, the effect size is probably pretty small but one of the studies was looking at a drop in productivity of 1.4% and concluding that that level of productivity loss justified better ventilation. Imagine if the whole world is missing out on that from poor ventilation. Imagine if the whole world is missing out on that because we are at 400 instead of 0. Again, not likely but the kind of thing that would have big (cumulative) downsides if true.
I tried looking at the physiological effects of CO2 and did not do as deep a dive as I would have liked but this paper claims that there is a dose response relationship between cerebral blood flow and CO2 concentration (in the blood) and that it really levels out beneath ~normal physiological levels. I take this to mean that there would be a small, but measurable, physiological response if I could remove all the CO2 from my blood, which they did by hyperventilating.
Along the way I started looking at physiological effects of O2 availability and, well, I have some words about a particular article I found. Look at this graph:
It looks like there is some homeostasis going on where your cerebral blood flow can go down because there is more oxygen in the blood (%CaO2) giving you the same amount delivered (%CDO2). The only issue is that they said “When not reported, DO2 was estimated as the product of blood flow and CaO2.” When I read that I felt like I was losing my mind. Doesn’t that defeat the whole purpose of looking at multiple studies? If you just assume that the effect is given by some relation, fill in data based on that assumption, and average out with real data of course you’re going to get something like the relation you put in. As one of the many not doctors in the world, maybe I should stay in my lane but this does strike me as a bit circular. I am not convinced that an increase in atmospheric O2 does not lead to an increase in the O2 delivered to the brain. Especially because decreases in O2 partial pressure are definitely related to decreases in O2 (and cognition) in the brain and it would be kind of weird if the curve was just totally flat after normal atmospheric levels[5].
I also found one very optimistic group claiming that breathing 100% O2 could increase cognitive performance in two main papers. They are both recent and from a small university so it makes sense that this didn’t get a ton off attention but that doesn’t really make me less skeptical that it’s just that easy. The first paper claimed 30% increase in motor learning and I would expect that effect size to decrease significantly upon replication.
All this leaves four main possibilities the way I see it:
My solution
Well, I don’t have the resources to do a randomized control trial. But, I do have the ability to make a CO2 scrubber and feed the treated air into a facemask so I can breathe it. If I do this, I’m not buying the parts until I confirm nobody leaves a comment just demolishing the central thesis, I would probably wait until spring as opening my windows seems like a big important step to having low ambient CO2[7] but would be pretty miserable for me while there’s still snow outside.
This is a chance to talk about some cool applications of chemistry. The idea is that CO2 can react with NaOH to form only aqueous products, removing the CO2 from the air. These can then react with Ca(OH)2 to yield a solid precipitate which can be heated to release the CO2 and reform the Ca(OH)2. This is, apparently, all pretty common for controlling the pH of fish tanks so that’s convenient and cheap.
I’ve already been trying to track my productivity along with a few interventions so I plan to just roll this in with that. This won’t be a blinded trial but I am happy to take a placebo win if it increases my productivity and if it doesn’t do anything measurable I’m really not interested in it.
As for oxygen enrichment, you can buy oxygen concentrators, nitrogen filters that people use for making liquid nitrogen instead of liquid air, medical grade oxygen, oxygen for other purposes, or make it with electrolysis. All of these strike me as being somewhat dangerous or quite expensive to do for long periods of time. Someone else on LessWrong wanted oxygen (for a much better and less selfish reason) and got some for divers/pilots. I would do that, but again, expensive.
With any luck, I will have a case study done on myself at some point and can update everyone with the results.
I don’t want to be harsh, the video is only a few minutes long, is made by a climate activist who already has some strong beliefs on CO2, and he did put his own mind on the line as a test case to make a point which I applaud. Given those reasons and that he seemed to have quite negative effects from the CO2 himself I think it is quite fair that he didn’t have a detailed counterargument presented.
https://pmc.ncbi.nlm.nih.gov/articles/PMC4892924/pdf/ehp.1510037.pdf
https://www.nature.com/articles/s41526-019-0071-6
The group used “astronaut-like subjects” which is fine but I don’t know if that generalizes to most other people.
Not hugely surprising though, we did evolve to use the atmospheric level so I wouldn’t be shocked if it was flat, just that this study didn’t convince me that it was flat.
I realized I did not talk about VOCs, volatile organic compounds, at all. They are just a wide variety of chemicals that permeate the modern world and are probably bad in ways we aren’t certain of.
As an aside, I would not be shocked if poor ventilation during the winter was a contributing factor to seasonal affective disorder but I don’t have that and did not look into anyone checking if it is true.