Airborne fraction

The airborne fraction is a scaling factor defined as the ratio of the annual increase in atmospheric CO
2 to the CO
2 emissions from anthropogenic sources. It represents the proportion of human emitted CO₂ that remains in the atmosphere. The fraction averages about 45%, meaning that approximately half the human-emitted CO
2 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 CO
2 for a given rate of human fossil-fuel burning. 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".

Changes in carbon sinks can affect the airborne fraction.

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