PCO2

pCO₂, pCO₂, or ${\displaystyle P_{{\ce {CO2}}}}$ is the partial pressure of carbon dioxide (CO₂), often used in reference to blood but also used in meteorology, climate science, oceanography, and limnology to describe the fractional pressure of CO₂ as a function of its concentration in gas or dissolved phases. The units of pCO₂ are mmHg, atm, torr, Pa, or any other standard unit of atmospheric pressure. The pCO₂ of Earth's atmosphere has risen from approximately 280 ppm (parts-per-million) to a mean 2019 value of 409.8 ppm as a result of anthropogenic release of carbon dioxide from fossil fuel burning.^{[citation needed]} This is the highest atmospheric concentration to have existed on Earth for at least the last 800,000 years.^[1]