New global observations of the terrestrial carbon cycle from GOSAT: Patterns of plant fluorescence with gross primary productivity

TLDR

Accurately closing the Earth’s carbon budget and predicting climate feedbacks requires precise knowledge of when, where, and how land–atmosphere CO₂ exchange occurs, yet uncertainties in terrestrial gross primary production and its seasonality remain large. The study aims to use global fluorescence data with plant physiological models to revolutionize carbon cycle research and improve future predictions. The authors use spaceborne measurements of solar‑induced chlorophyll fluorescence, which correlate linearly with gross primary production, to estimate GPP. Fluorescence alone predicts GPP as well or better than traditional vegetation indices, though its correlation weakens in boreal summer due to regional discrepancies, demonstrating that chlorophyll fluorescence retrievals offer direct global constraints and a new perspective on the carbon cycle.

Abstract

Our ability to close the Earth's carbon budget and predict feedbacks in a warming climate depends critically on knowing where, when and how carbon dioxide is exchanged between the land and atmosphere. Terrestrial gross primary production (GPP) constitutes the largest flux component in the global carbon budget, however significant uncertainties remain in GPP estimates and its seasonality. Empirically, we show that global spaceborne observations of solar induced chlorophyll fluorescence – occurring during photosynthesis – exhibit a strong linear correlation with GPP. We found that the fluorescence emission even without any additional climatic or model information has the same or better predictive skill in estimating GPP as those derived from traditional remotely-sensed vegetation indices using ancillary data and model assumptions. In boreal summer the generally strong linear correlation between fluorescence and GPP models weakens, attributable to discrepancies in savannas/croplands (18–48% higher fluorescence-based GPP derived by simple linear scaling), and high-latitude needleleaf forests (28–32% lower fluorescence). Our results demonstrate that retrievals of chlorophyll fluorescence provide direct global observational constraints for GPP and open an entirely new viewpoint on the global carbon cycle. We anticipate that global fluorescence data in combination with consolidated plant physiological fluorescence models will be a step-change in carbon cycle research and enable an unprecedented robustness in the understanding of the current and future carbon cycle.