[nate_meurer]

> Cognitive decline starts above 600 ppm according to air quality studies.

According to an older, small study of short duration (Mendell and Fisk at LBNL), the results of which are heavily disputed. Since 600 ppm isn't too much higher than the current level of 400+ ppm, this study is the one most commonly cherry-picked in order to instill fear in people that climate change is getting ready to damage our brains.

Just for comparison, the CO2 composition of exhaled breath is around 40,000 ppm (~4%), which is the reason that it's totally normal for CO2 concentrations in enclosed spaces like bedrooms and classrooms to reach several thousand ppm. CO2 levels in submarines average well over ten times atmospheric, and routinely reach well over 10,000 ppm.

In none of these situations have researchers found a clear and convincing long-term impact on cognitive performance. Short term yes, but our bodies and brains adapt. Some compensations appear incomplete, but others are possibly sufficient to incur health benefits from high CO2 concentrations. Notably, high CO2 levels cause blood vessels to dilate, increasing the flow of oxygen to tissues including the brain. There is in fact ongoing research into medical therapies using concentrated CO2.

[throwawayffffas]

As far as I am aware astronauts that were experiencing concentrations above 3000 ppm for presumably weeks to months reported mental viscosity(brain fog) and headaches.

A definite global health concern is the increase in blood bicarbonate levels which chronically impact available calcium and phosphorus levels.

Additionally the higher CO2 levels increase plant growth which impacts the plants mineral absorption, there are less naturally occurring micronutrients in our crops than there used to be just 20 years ago.

These things are far from apocalyptic but have to be taken into account going forward when updating existing food enrichment programs.

I believe you are conflating hyperbaric oxygen treatment with CO2. I could not find references to concentrated CO2 treatments. While exhaled air is about 4% CO2, breathing air with CO2 at these concentrations is immediately dangerous.

Additionally I do not believe that has been any study comparing relative cognitive performance of continuously operating in different low concentration environments, all studies focus on short term, high concentrations and for obvious practical reasons treat the atmospheric level as the baseline.

As far as we know operating in pre-industrial levels of CO2 280ppm improves, deteriorates or has no effect on cognition compared to modern levels.

[nate_meurer]

> astronauts... reported mental viscosity(brain fog) and headaches

I can think of plenty of excellent reasons the environment in the space station would lead to physiological issues. Sleep disturbance, stress, restrictions on diet and exercise, and the many severe effects of microgravity all come to mind. Again, you have to ignore humanity's extensive experience with other high-CO2 environments like submarines in order to believe that it's a significant factor compared to those other stressors.

> A definite global health concern is the increase in blood bicarbonate levels

It's hardy definite. It's another junk-science "study" out of Australia that took two epidemiological trends (bicarbonate level and mineral levels in blood over 20 years) and tried to interpret correlation as causation. You can use this kind of data-dredging to propose correlation between all kinds of unrelated trends. I'm seeing headlines blaming climate change for the obesity epidemic, for example, and you can be sure there's a junk science study behind every headline. In this case, I'm aware of no evidence from well-controlled studies (i.e., actual science) showing a causal chain from moderately elevated CO2 to physiological mineral deficiencies in real life. Again, we have lots of long-term data from high-CO2 environments like submarines. Show me some numbers.

> higher CO2 levels increase plant growth which impacts the plants mineral absorption, there are less naturally occurring micronutrients in our crops than there used to be just 20 years ago.

More questionable headline-generating studies. Yes, isolated increases in CO2 can cause carbohydrate dilution and subsequent changes in water usage and mineral uptake, but it also universally increases plant growth, and in many plants it increases production of other phytochemical nutrients. This is an extremely complex topic, and it's reductive to the point of absurdity to blame atmospheric CO2 for trends that are overwhelmingly influenced by soil depletion, water usage, and chemical fertilization.

Think about this logically: A substantial portion of our fruits and vegetables are grown in greenhouses. In the Netherlands-- the world's second-largest food exporter-- over one-fifth of produce is grown in greenhouses. Almost all modern greenhouses employ carbon dioxide enrichment, typically doubling the level of the atmosphere. If there's a brewing crisis of CO2-induced nutrient deficiency, don't you think the climate alarmists would be warning us about greenhouses? The fact that they aren't should tell you something.

It's common for people to filter on the latest fear-mongering headlines. Maybe these things are true, but "studies" like these that appear in corporate media headlines can't tell us one way or the other.

> I could not find references to concentrated CO2 treatments

It's a young field of research to be sure, but it took me about five seconds to find a bunch of recent papers. Here's the first result google gave me:

https://pmc.ncbi.nlm.nih.gov/articles/PMC11763298/ | Effects of Carbon Dioxide Therapy on Skin Wound Healing

[throwawayffffas]

I am noticing a pattern where studies are dismissed as junk based on preformed opinions, specifically about "climate alarmists" you should consider why you are so quick to dismiss the majority of the research in indoor air quality.

There is one notable study about submariners that did not find impairment in one simulation, the consensus about it is selection bias and training. Submariners are not the average population, both in terms of general fitness and in terms of self selecting, people who can't cope or perform in the high CO2 environment quit or fail. The finding of other studies is brain fog not total incompetence.

> https://pmc.ncbi.nlm.nih.gov/articles/PMC11763298/ | Effects of Carbon Dioxide Therapy on Skin Wound Healing

That's cool, a bit of nuance though the studies are discussing applying CO2 directly at afflicted tissue not through breathing.

[nate_meurer]

No, I pointed out specific flaws in those papers. You're just pretending that I'm dismissing them out of hand so you don't have to read them yourself.

Once again, the Australian study that's the source of your original assertion was very small (n=4 in each study group) and very short term (only a few hours of study time). And the paper about bicarbonate levels is a great example of data dredging, where coincident trends are implied to be causative with no further support.

I'm not saying the conclusions are wrong. They could both be right. I'm just saying that their methods are too poor to draw any useful conclusions.

> people who can't cope or perform in the high CO2 environment quit or fail

So here you are dismissing evidence out of hand by pretending not to understand it. Even if submariners are selected based on CO2 tolerance (which is silly), it wouldn't matter. The point is that the US Navy has had a large population to study for long periods of time in highly controlled environments. The same men can be examined before, during, and after exposure to very high concentrations of CO2, while other environmental variables are held constant, and the navies of multiple countries have data from many such populations over decades. That's what produces useful data, in contrast to that tiny, short Australian study you seem to be attached to.