The airborne fraction is a scaling factor defined as the ratio of the annual increase in atmospheric to the emissions from anthropogenic sources.^[1] It represents the proportion of human emitted that remains in the atmosphere. The fraction averages about 45%, meaning that approximately half the human-emitted is absorbed by ocean and land surfaces. There is some evidence for a recent increase in airborne fraction, which would imply a faster increase in atmospheric for a given rate of human fossil-fuel burning.^[2] However, other sources suggest that the "fraction of carbon dioxide has not increased either during the past 150 years or during the most recent five decades".^[3][4]

Changes in carbon sinks can affect the airborne fraction.

References