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 human 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. Changes in carbon sinks can affect the airborne fraction.
Observations over the past six decades show that the airborne fraction has remained relatively stable at around 45%. This indicates that the land and ocean's capacity to absorb CO2 has kept up with the rise in human CO2 emissions, despite the occurrence of notable interannual and sub-decadal variability, which is predominantly driven by the land's ability to absorb CO2.
- Greenhouse gas
- Carbon dioxide in Earth's atmosphere
- Total Carbon Column Observing Network
- Atmospheric carbon cycle
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