Alternate histories: synthetic large ensembles of sea-air CO 2 flux

• Published in: Global Biogeochemical Cycles
• Main Authors: Olivarez, Holly C., Lovenduski, Nicole S., Brady, Riley X., Fay, Amanda R., Gehlen, Marion, Gregor, Luke, Landschützer, Peter, Mckinley, Galen A., Mckinnon, Karen A., Munro, David R.
• Other Authors: University of Colorado Boulder, Department of Atmospheric and Oceanic Sciences and Institute of Arctic and Alpine Research, Columbia University New York, Lamont-Doherty Earth Observatory (LDEO), Laboratoire des Sciences du Climat et de l'Environnement Gif-sur-Yvette (LSCE), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Direction de Recherche Fondamentale (CEA) (DRF (CEA)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA), Institute of Biogeochemistry and Pollutant Dynamics ETH Zürich (IBP), Department of Environmental Systems Science ETH Zürich (D-USYS), Eidgenössische Technische Hochschule - Swiss Federal Institute of Technology Zürich (ETH Zürich)-Eidgenössische Technische Hochschule - Swiss Federal Institute of Technology Zürich (ETH Zürich), Max Planck Institute for Meteorology (MPI-M), Max-Planck-Gesellschaft, Department of Statistics Los Angeles, University of California Los Angeles (UCLA), University of California (UC)-University of California (UC), National Oceanic and Atmospheric Administration (NOAA)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2022
• Subjects: global carbon cycle; air-sea CO 2 flux; ocean carbon uptake; large ensemble; Earth system modeling; decadal trends; [SDU]Sciences of the Universe [physics]; Southern Ocean
• Online Access: https://insu.hal.science/insu-03721925; https://insu.hal.science/insu-03721925/document; https://insu.hal.science/insu-03721925/file/Global%20Biogeochemical%20Cycles%20-%202022%20-%20Olivarez%20-%20Alternate%20Histories%20Synthetic%20Large%20Ensembles%20of%20Sea%25E2%2580%2590Air%20CO2%20Flux.pdf; https://doi.org/10.1029/2021GB007174

International audience We use a statistical emulation technique to construct synthetic ensembles of global and regional sea-air carbon dioxide (CO 2 ) 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 CO 2 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 CO 2 flux (i.e., enhanced ocean CO 2 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 CO 2 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 CO 2 flux trends, and furthers understanding of the role of internal and external processes in driving observed sea-air CO 2 flux variability.