Amazon Basin as the Key Uncertainty for Terrestrial CO2 Uptake Enhancement

Abstract:

In the circumstance where increasing anthropogenic CO₂ emissions aggravate climate change, it is a major concern how long the CO₂ uptake enhancement continues to mitigate the increasing atmospheric CO₂ concentration. The net-zero emissions goal set under the Paris agreement is promising to facilitate world-wide efforts to reduce CO₂ emissions from fossil fuel burning and cement production. At the same time, the role of the natural biogeochemical cycles on current CO₂ sequestration needs to be better understood. The CO₂ uptake enhancement in both the land and ocean is well supported by evidences from observations and model experiments, but up to the decade of 2000s. Our current understanding about the continuity of the CO₂ uptake enhancement beyond the 2000s remains equivocal.

In this analysis, we assess the current status of the CO₂ uptake enhancement, including the continuity of uptake enhancement in the land and ocean, agreements and disagreements between the modelling methods, and the factors and uncertainties that influence the level of uptake enhancement. Focusing on recent trends and budget changes between decades, we investigate the multi-model simulations of net land and ocean CO₂ fluxes from atmospheric inversions, DGVMs, and GOBMs from work undertaken in the Global Carbon Project. We detail global and regional trends of net CO₂ flux through investigation of the long-term and short-term periods (1980−2017 and 2000−2017, respectively) with the aim of elaborating the status of consistency between the current atmospheric inversions and biogeochemical models. Finally, we discuss potential scenarios about projection of the global CO₂ uptake enhancement arisen from the top-down and bottom-up modelling and the cause for the different projections, which turn out to be inconsistent trend estimates for Amazon basin.