You know that CO2 concentration is at 421 ppm, (0.0421%) up from 280 ppm in 1850? That change is negligible compared to the 21% oxygen. Standing in a crowd or being inside causes a much higher variation of the oxygen concentration. Even moving up 2 meters changes the amount of oxygen molecules per volume by more than that.
With 43 kcal/100ml you need about 4.6 liters or 5 qts to satisfy your caloric needs (2000kcal/day). If you even out the intake over the whole day, alcohol levels should be low enough to keep you functioning. Beer also contains a bit of protein and low levels of sodium, potassium and magnesium.
Long term, you’ll get scurvy after a few months due to lack of vitamin C and liver cirrhosis from the sustained alcohol use.