Projected High-Resolution CO2 Concentrations over the Amazon Rainforest under the SSP5-8.5 Pathway through the End of the Century

The continued degradation of the Amazon rainforest, exacerbated by rising air temperatures and increased hydric stress in recent decades, is altering its capacity to absorb carbon. However, the scarcity of local observations and the difficulty of representing the vast and diverse Amazon biome in numerical models make it challenging to accurately quantify carbon exchanges across the region. Consequently, determining whether the Amazon as a whole currently functions as a carbon source or sink remains a key priority for future research.

In this study, we conducted high-resolution simulations of CO₂ concentrations over the Amazon rainforest using the Weather Research and Forecasting Greenhouse Gas (WRF-GHG) model for April and September of selected years through the end of the century. Initial and boundary conditions for
meteorological variables and background CO₂ concentrations were derived from projections of the Intergovernmental Panel on Climate Change (IPCC) worst-case climate scenario based on the Coupled Model Intercomparison Project 6 (CMIP6) under the Shared Socioeconomic Pathway 5-8.5 (SSP5-8.5). To ensure consistency, SSP5-8.5 land-use projections from the Land-Use Harmonization version 2 (LUH2) dataset were reclassified to match WRF-GHG land-use categories. All simulations included a 15-day spin-up period, followed by a two-day rolling simulation framework for the target month.

The results indicate that by 2050, CO₂ concentrations over the Amazon are projected to reach approximately 550-650 ppm, exceeding the global, Northern Hemisphere, and Southern Hemisphere annual mean concentrations for that year, which are estimated at about 563 ppm, 567 ppm, and 558
ppm, respectively. Notably, the simulations also suggest a slight reduction in Net Ecosystem Exchange (NEE) fluxes between 2030 and 2050.