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Bennett, Brian F.; Salawitch, Ross J.; McBride, Laura A.; Hope, Austin P.; Tribett, Walter R.

Quantification of the Airborne Fraction of Atmospheric CO2 Reveals Stability in Global Carbon Sinks Over the Past Six Decades

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  • Medientyp: E-Artikel
  • Titel: Quantification of the Airborne Fraction of Atmospheric CO2 Reveals Stability in Global Carbon Sinks Over the Past Six Decades
  • Beteiligte: Bennett, Brian F.; Salawitch, Ross J.; McBride, Laura A.; Hope, Austin P.; Tribett, Walter R.
  • Erschienen: American Geophysical Union (AGU), 2024
  • Erschienen in: Journal of Geophysical Research: Biogeosciences
  • Sprache: Englisch
  • DOI: 10.1029/2023jg007760
  • ISSN: 2169-8953; 2169-8961
  • Entstehung:
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  • Beschreibung: <jats:title>Abstract</jats:title><jats:p>The airborne fraction of atmospheric CO<jats:sub>2</jats:sub> (AF), defined as the annual global CO<jats:sub>2</jats:sub> growth rate (<jats:italic>d</jats:italic>CO<jats:sub>2</jats:sub>/<jats:italic>dt</jats:italic>) divided by the total emission of CO<jats:sub>2</jats:sub> from combustion of fossil fuels and land use change (LUC), has a long‐term average of ∼0.44 over the past six decades. When quantifying trends in AF it is important to account for inter‐annual variability in <jats:italic>d</jats:italic>CO<jats:sub>2</jats:sub>/<jats:italic>dt</jats:italic> due to natural factors such as the El Niño Southern Oscillation (ENSO) and major volcanic eruptions, as well as assumptions regarding LUC. Here, a multiple linear regression model is used to compute <jats:italic>d</jats:italic>CO<jats:sub>2</jats:sub>/<jats:italic>dt</jats:italic> as a function of anthropogenic CO<jats:sub>2</jats:sub> emissions, ENSO indices, and stratospheric aerosol optical depth (a proxy for major volcanic eruptions), for numerous time series of the emission of CO<jats:sub>2</jats:sub> due to LUC (<jats:italic>E</jats:italic><jats:sub>LUC</jats:sub>). For 20 out of 21 previously published <jats:italic>E</jats:italic><jats:sub>LUC</jats:sub> time series, the trend in AF adjusted for natural variability (AF<jats:sup>ADJ</jats:sup>) over 1959 to 2021 exhibits a trend that is statistically indistinguishable from zero and lacks statistical significance at the 95% confidence interval. Therefore, it is most likely that the relative efficacy of the combined global terrestrial biosphere and oceanic carbon sinks has been fairly constant on a global scale over the past six decades. Since the trend in AF exhibits considerable variability depending on which <jats:italic>E</jats:italic><jats:sub>LUC</jats:sub> time series is used, more precise knowledge of the actual value of the AF trend will require resolving the current large differences in various estimates of <jats:italic>E</jats:italic><jats:sub>LUC</jats:sub>.</jats:p>