What principle is used in the above diagram to calculate the amount of carbon dioxide that is absorbed by land?

The principle used to calculate the amount of carbon dioxide absorbed by land is typically based on the carbon cycle, which includes processes such as photosynthesis and respiration. Plants absorb CO2 during photosynthesis, converting it into organic matter. The balance between the amount of CO2 taken up by vegetation and the amount released through respiration and decomposition helps quantify the net carbon sequestration by land. This measurement can be influenced by factors like land use, vegetation type, and climate.