User:Paul JCW/Airborne fraction

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The airborne fraction is a scaling factor defined as the ratio of the annual increase in atmospheric CO2 to the emissions from human sources. 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. 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.

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Anthropogenic CO2 that is released into the atmosphere is partitioned into three components: approximately 45% remains in the atmosphere (referred to as the airborne fraction), while about 24% and 31% are absorbed by the ocean s (ocean sink) and terrestrial biosphere (land sink), respectively. If the airborne fraction increases, it means that a greater proportion of the CO2 released by humans ultimately remains in the atmosphere. This has implications for future projections of atmospheric CO2 levels, which must be adjusted to account for this trend. The question of whether the airborne fraction is rising, remaining steady at approximately 45%, or declining remains a matter of debate. However, resolving this question is critical for comprehending the global carbon cycle and has relevance for policymakers and the general public.

An argument was presented that the airborne fraction of CO2 released by human activities, particularly through fossil fuel emissions, cement production, and land-use changes, is on the rise. Since 1959, the average CO2 airborne fraction has been 0.43, but it has shown an increase of approximately 0.2% per year over that period. On the other hand, the findings of another group suggest that the CO2 airborne fraction has declined by 0.014 ± 0.010 per decade since 1959. This indicates that the combined land-ocean sink has expanded at a rate that is at least as rapid as anthropogenic emissions.

The trend analyses of airborne fraction may be affected by external natural occurrences, such as the El Niño-Southern Oscillation (ENSO), volcanic eruptions, and other similar events. It is possible that the methodologies used in these studies to analyze the trend of airborne fraction are not robust, and therefore, the conclusions drawn from them are not warrented. At present, studies examining the trends in airborne fraction are producing contradictory outcomes, with emissions linked to land use and land cover change representing the most significant source of uncertainty.

The next step is to analyzing the model and formula for calculating airborne fraction.