1. Direct effects on brain physiology: When CO2 levels rise in the blood (hypercapnia), it causes vasodilation of cerebral blood vessels. While this initially increases blood flow, sustained elevation disrupts the brain's normal pH balance, affecting neural function.

2. Acid-base imbalance: Elevated CO2 in the blood forms carbonic acid, decreasing blood pH. This acidosis affects enzyme function, neurotransmitter activity, and neuronal excitability throughout the brain.

3. Oxygen displacement: While not typically reaching dangerous levels in standard indoor environments, higher CO2 concentrations can slightly reduce oxygen availability to brain tissues in enclosed spaces.

4. Inflammatory responses: Research suggests prolonged exposure to elevated CO2 may trigger low-grade neuroinflammatory responses, potentially impairing cognitive processes.

5. Disruption of neurotransmitter systems: CO2-induced acidosis appears to affect several neurotransmitter systems, particularly GABA and glutamate, which are critical for cognitive functions like attention, memory, and decision-making.

Studies have shown measurable cognitive effects at CO2 concentrations as low as 1,000 ppm, with more significant impairment at 2,500+ ppm - levels commonly found in poorly ventilated meeting rooms, classrooms, and offices.

As for indoor vs outdoor:

> Rising atmospheric CO2 levels from global warming don't pose the same cognitive risks as elevated indoor CO2. While indoor environments can reach 1,000-5,000+ ppm, causing measurable cognitive decline through mechanisms like acid-base imbalance and neurotransmitter disruption, global atmospheric CO2 is only about 420 ppm. Even with projected increases to 500-1,000 ppm by 2100 in worst-case scenarios, these levels remain below thresholds for significant cognitive impairment. Our bodies can also better adapt to gradual atmospheric changes compared to rapid indoor CO2 accumulation, making climate change impacts the primary concern rather than direct cognitive effects.