The navy routinely operates submarines at 3500ppm or more, and they've been conducting studies since the 60s which have failed to show a cognitive decline from levels as high as 30,000ppm.
Here's a HN comment with a good summary.
(To the other comment, the 2021 paper I linked is not "pop science".)
The context of the paper you linked is "stressors in a disabled submarine". It's not a summary of the Navy's research. It does contain a few paragraphs out of nearly 100 pages that briefly summarizes a few relevant studies, both civilian and military.
Here's the relevant section:
>While some studies have found that elevated CO2 may impair cognitive functions including decision making (Satish et al., 2012), attention (Schaefer, 1951), mental efficiency (Karlin, 1945), and mathematical processing (Sayers, Smith, Holland, & Keatinge, 1987), these findings are not consistently replicated (Rodeheffer, Chabal, Clarke, & Fothergill, 2018; Ryder et al., 2017; X. Zhang, Wargocki, & Lian, 2016; X. Zhang, Wargocki, Lian, & Thyregod, 2016). In fact, many studies have been unable to establish a relationship between CO2 exposure and cognitive deficits (e.g., Bloch- Salisbury, 2000; Francis et al., 2002; Sheehy, Kamon, & Kiser, 1982; Vercruyssen, Kamon, & Hancock, 2007).
It lists 3 studies showing a cognitive impact impact. 2 out of the 3 show that there is a cognitive impact at extreme levels far beyond the levels that build up in a conference room, or levels that we'll be exposed to because of increased atmospheric C02.
--Sayers, Smith, Holland, & Keatinge, 1987 This study showed a cognitive impact at 65,000ppm, but nothing at 45,000ppm.
--Schaefer, 1951 Showed that submariners were slightly affected after prolonged exposure to 30,000ppm
Then it lists 7 studies showing no impact on cognition even at very high levels. Out of 10 studies listed, 1 civilian study shows cognitive impact at 1,000ppm. The preponderance of the evidence indicates that that study is a fluke. By the way, this study is the one that kicked off the whole normal indoor levels of C02 make you dumber thing in the first place.
This statement:
>the relationship between CO2 exposure and cognition is debated
is in the context of whether or not concentrations of up to 30,000ppm seen in a submarine disaster will impact cognition, not whether 1,000ppm in a conference room will.
FWIW, CO2 can cause cognitive decline. I mean hypoxia is a thing. But usually CO2 levels are a correlating factor (confounder) rather than the direct cause. So we can use it as a tool to help, but it isn't the problem. These types of things are the hard part about causality and why we are so easily fooled (because it makes sense and reflects what we (naively) observe).