The Orbiting Carbon Observatory-2 (OCO-2) and in situ CO2 data suggest a larger seasonal amplitude of the terrestrial carbon cycle compared to many dynamic global vegetation models

• Published in: Remote sensing of environment Vol. 312; p. 114326
• Main Authors: Lei, Ruixue, Poe, Jeralyn, Huntzinger, Deborah, Liu, Junjie, Stich, Stephen, Baker, David F., Feng, Leyang, Gaeta, Dylan C., Huang, Ziting, Miller, Scot M.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.10.2024
• Subjects: Dynamic global vegetation models; Global carbon cycle; Net biome productivity; OCO-2; Seasonal-cycle amplitude; OCO-2; Dynamic global vegetation models; Seasonal-cycle amplitude; Net biome productivity; Global carbon cycle
• ISSN: 0034-4257
• DOI: 10.1016/j.rse.2024.114326

Existing, state-of-the-art vegetation models disagree by a factor of four on the seasonal amplitude of the global, terrestrial carbon cycle. This seasonal amplitude is likely increasing over time due to climate change, and disagreements among vegetation models therefore complicate efforts to quantify how climate change is impacting the carbon cycle. We evaluate the seasonal cycle of terrestrial CO2 fluxes from an ensemble of vegetation models using CO2 observations from the Orbiting Carbon Observatory-2 (OCO-2), in situ CO2 observations, and inverse models. We find that vegetation models with a larger seasonal amplitude are also more sensitive to climate change, in that they exhibit a larger increase in amplitude during the past century. Furthermore, ten of the 17 models analyzed have a seasonal amplitude smaller than an ensemble of inverse CO2 flux estimates based on OCO-2 observations; these discrepancies are largest across the Eastern US, boreal Asia, the Congo, and the Amazon. Vegetation models with larger seasonal amplitudes, when run through an atmospheric transport model (i.e. GEOS-Chem), typically exhibit a better fit compared to atmospheric CO2 observations. We also find that vegetation models produce similar seasonal amplitudes of net CO2 fluxes using very different combinations of gross primary production and respiration, making these model disagreements challenging to resolve. •Many vegetation models exhibit smaller amplitudes than inverse estimates.•Vegetation models with a larger amplitude also show a larger multi-decadal trend.•Models yield similar amplitudes with different combinations of GPP and Reco.