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Alternate histories: synthetic large ensembles of sea-air CO2 flux

Abstract : We use a statistical emulation technique to construct synthetic ensembles of global and regional sea-air carbon dioxide (CO2) flux from four observation-based products over 1985-2014. Much like ensembles of Earth system models that are constructed by perturbing their initial conditions, our synthetic ensemble members exhibit different phasing of internal variability and a common externally forced signal. Our synthetic ensembles illustrate an important role for internal variability in the temporal evolution of global and regional CO2 flux and produce a wide range of possible trends over 1990-1999 and 2000-2009. We assume a specific externally forced signal and calculate the rank of the observed trends within the distribution of statistically modeled synthetic trends during these periods. Over the decade 1990-1999, three of four observation-based products exhibit small negative trends in globally integrated sea-air CO2 flux (i.e., enhanced ocean CO2 absorption with time) that are within one standard deviation of the mean in their respective synthetic ensembles. Over the decade 2000-2009, however, three products show large negative trends in globally integrated sea-air CO2 flux that have a low rate of occurrence in their synthetic ensembles. The largest positive trends in global and Southern Ocean flux over 1990-1999 and the largest negative trends over 2000-2009 fall nearly two standard deviations away from the mean in their ensembles. Our approach provides a new perspective on the important role of internal variability in sea-air CO2 flux trends, and furthers understanding of the role of internal and external processes in driving observed sea-air CO2 flux variability.
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https://hal-insu.archives-ouvertes.fr/insu-03721925
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Submitted on : Tuesday, August 30, 2022 - 3:57:26 PM
Last modification on : Tuesday, August 30, 2022 - 4:21:16 PM

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Holly C. Olivarez, Nicole S. Lovenduski, Riley X. Brady, Amanda R. Fay, Marion Gehlen, et al.. Alternate histories: synthetic large ensembles of sea-air CO2 flux. Global Biogeochemical Cycles, American Geophysical Union, 2022, 36 (6), pp.e2021GB007174. ⟨10.1029/2021GB007174⟩. ⟨insu-03721925⟩

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