> One could estimate exactly how much higher with some differential equations, but certainly in some cases it is possible to push things over the limit where there are now problems, everything else remaining the same.
It's obviously in the direction of higher indoor CO2 levels, but the effect just isn't that big if you're talking about your indoor levels being 2000ppm. It's not the cause of that.
I'll see if I can math up some numbers later to quantify.
> Moreover, those buildings likely now have much less air exchange than when designed now that they use AC instead of open windows, forced air heat instead of unsealed fireplaces (which turn over a lot of air), and possibly have been updated to more airtight doors and windows.
Yes, these are the causes. Well insulated homes are legitimately great, but now we're finding out that ventilation is also quite important and wasn't well enough planned for in many cases.
It's also that CO2 wasn't easy to measure decades ago. I'm sure many homes had high levels even with no door seals and leaky windows, just nobody had a great way to know or care. I'm sure ways existed, to be clear, but it wasn't like today where you can grab a monitor on amazon on a whim.
