15 Dec 2022
15 Dec 2022

Characteristics of Interannual Variability in Space-based XCO2 Global Observations

Yifan Guan1, Gretchen Keppel-Aleks1, Scott C. Doney2, Christof Petri3, Dave Pollard4, Debra Wunch5, Frank Hase6, Hirofumi Ohyama7, Isamu Morino7, Justus Notholt3, Kei Shiomi9, Kim Strong5, Rigel Kivi10, Matthias Buschmann3, Nicholas Deutscher12, Paul Wennberg11, Ralf Sussmann8, Voltaire A. Velazco12,13, and Yao Té14 Yifan Guan et al.
  • 1Department of Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI, 48105, USA
  • 2Department of Environmental Sciences, University of Virginia, Charlottesville, VA, 22903, USA
  • 3Institute of Environmental Physics, Physics Department, University of Bremen, Bremen, 28359, Germany
  • 4National Institute of Water and Atmospheric Research, Omakau, 9377, New Zealand
  • 5Department of Physics, University of Toronto, Toronto, M5S 1A7, Canada
  • 6Institute of Meteorology and Climate Research - Atmospheric Trace Gases and Remote Sensing, Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen, 76344, Germany
  • 7National Institute for Environmental Studies, Tsukuba, Ibaraki 305-0053, Japan
  • 8Institute of Meteorology and Climate Research - Atmospheric Environmental Research, Karlsruhe Institute of Technology, Garmisch-Partenkirchen, 82467, Germany
  • 9Earth Observation Research Center, Japan Aerospace Exploration Agency, Tsukuba, Ibaraki, 305-8505, Japan
  • 10Space and Earth Observation Centre, Finnish Meteorological Institute, Sodankylä, 99600, Finland
  • 11Divisions of Engineering and Applied Science and Geological and Planetary Science, California Institute of Technology, Pasadena, CA, 91125, USA
  • 12Centre for Atmospheric Chemistry, School of Earth, Atmospheric and Life Sciences, University of Wollongong, Wollongong, 2522, Australia
  • 13Deutscher Wetterdienst, Meteorological Observatory, Hohenpeissenberg, 82383, Germany
  • 14Laboratoire d'Etudes du Rayonnement et de la Matière en Astrophysique et Atmosphères, French National Centre for Scientific Research, Paris, 75016, France

Abstract. Atmospheric carbon dioxide (CO2) accounts for the largest radiative forcing among anthropogenic greenhouse gases. There is, therefore, a pressing need to understand the rate at which CO2 accumulates in the atmosphere, including the interannual variations (IAV) in this rate. IAV in the CO2 growth rate is a small signal relative to the long-term trend and the mean annual cycle of atmospheric CO2, and IAV is tied to climatic variations that may provide insights into long-term carbon-climate feedbacks. Observations from the Orbiting Carbon Observatory-2 (OCO-2) mission offer a new opportunity to refine our understanding of atmospheric CO2 IAV since the satellite can measure over remote terrestrial regions and the open ocean where traditional in situ CO2 monitoring is difficult. In this study, we analyze the IAV of column-averaged dry air CO2 mole fraction (XCO2) from OCO-2 between September 2014 to June 2021. The amplitude of IAV variations is up to 1.2 ppm over the continents and around 0.4 ppm over the open ocean. Across all latitudes, the OCO-2 detected XCO2 IAV shows a clear relationship with ENSO-driven variations that originate in the tropics and are transported poleward. The XCO2 IAV timeseries shows similar zonal patterns compared to ground-based in situ observations and with column observations from the Total Carbon Column Observing Network (TCCON). At lower degrees of aggregation (i.e., 5°x5° grid cells), there are larger inconsistencies with TCCON suggesting that one or both of the observing systems are affected by bias or systematic retrieval issues that are of a similar magnitude to the IAV signal. Our results suggest that OCO-2 IAV provides meaningful information about climate-driven variations in carbon fluxes and provides new opportunities to monitor climate-driven variations in CO2 over open ocean and remote regions.

Yifan Guan et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-1022', Christopher O'Dell, 04 Jan 2023
  • RC2: 'Comment on egusphere-2022-1022', Anonymous Referee #1, 05 Jan 2023

Yifan Guan et al.


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Short summary
We characterize the spatial-temporal pattern of interannual variability (IAV) in atmospheric CO2 based on NASA’s Orbiting Carbon Observatory-2 (OCO-2). CO2 variation is strongly impact by climate events, with higher anomalies during El Nino years. We show high correlation in IAV between space-based and ground-based CO2 from long-term sites. Because OCO-2 has near-global coverage, our paper provides a roadmap to study IAV where in-situ observation is sparse, such as open oceans and remote lands.