Look at your CMP (Comprehensive Metabolic Panel) blood test results. It has a test named Carbon Dioxide. This test may have a reference range of 20-32 mmol/L. Subtract your value from the max value -- that's your leftover buffer as the atmospheric CO2 rises, although serious intermittent problems are risked at a level of 31 itself. There is a more specific blood gas test that only a hospital can perform.

Fwiw, my value reliably went down after I replaced citrate mineral supplements (calcium and magnesium) with glycinate capsules.