Atmospheric CO ₂ inversion reveals the Amazon as a minor carbon source caused by fire emissions, with forest uptake offsetting about half of these emissions

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Basso, Luana S. ; Wilson, Chris ; Chipperfield, Martyn P. ; Tejada, Graciela ; Cassol, Henrique L. G. ; Arai, Egidio ; Williams, Mathew ; Smallman, T. Luke ; Peters, Wouter ; Naus, Stijn ; Miller, John B. ; Gloor, Manuel

• Document type: Journal article
• Source: Atmospheric Chemistry and Physics; v. 23, n. 17, p. 39-pg., 2023-09-01.

Abstract

Tropical forests such as the Amazonian rainforests play an important role for climate, are large carbon stores and are a treasure of biodiversity. Amazonian forests are being exposed to large scale deforestation and degradation for many decades which declined between 2005 and 2012 but more recently has again increased with similar rates as in the 2007/2008. The resulting forest fragments are exposed to substantially elevated temperatures in an already warming world. These changes are expected to affect the forests and an important diagnostic of their health and sensitivity to climate variation is their carbon balance. In a recent study based on CO2 atmospheric vertical profile observations between 2010 and 2018, and an air column budgeting technique to estimate fluxes, we reported the Amazon region as a carbon source to the atmosphere, mainly due to fire emissions. Instead of an air column budgeting technique, we use here an inverse of the global atmospheric transport model, TOMCAT, to assimilate CO2 observations from Amazon vertical profiles and global flask measurements. We thus estimate inter- and intra-annual variability in the carbon fluxes, trends over time and controls for the period 2010-2018. This represents the longest Bayesian inversion of these atmospheric CO2 profile observations to date. Our analyses indicate that the Amazon is a small net source of carbon to the atmosphere (mean 2010-2018 = 0.13 +/- 0.17 PgC y(-1), where 0.17 is the 1-sigma uncertainty), with the majority of the emissions coming from the eastern region (77 % of total Amazon emission). Fire is the primary driver of the Amazonian source (0.26 +/- 0.13 PgC y(-1)), however the forest uptake likely removes around half of the fire emissions to the atmosphere (-0.13 +/- 0.20 PgC y(-1)). The largest net carbon sink was observed in the western-central Amazon region (72 % of the fire emissions). We find larger carbon emissions during the extreme drought years (such as 2010, 2015 and 2016), correlated with increases in temperature, cumulative water deficit and burned area. Despite the increase in total carbon emissions during drought years, we do not observe a significant trend over time in our carbon total, fire and net biome exchange estimates between 2010 and 2018. Our analysis thus cannot provide clear evidence for a weakening of the carbon uptake by Amazonian tropical forests. (AU)

• FAPESP's process: 08/58120-3 - Carbon tracker and water availability controls of land use and climate changes
• Grantee: Humberto Ribeiro da Rocha
• Support Opportunities: Research Program on Global Climate Change - Thematic Grants
• FAPESP's process: 18/14423-4 - Modeling a decade of carbon gross emissions from forest fires in the Amazon: Conciliating the bottom-up and top-down views of the problem
• Grantee: Henrique Luis Godinho Cassol
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 18/14006-4 - Estimation of Amazon Greenhouse Gas balances from atmospheric concentrations using inverse modelling of atmospheric transport
• Grantee: Luana Santamaria Basso
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 19/21789-8 - The use of multivariate techniques and neural network predictions to the greenhouse gases database, climate parameters and biomass burning at Amazon
• Grantee: Luciana Vanni Gatti
• Support Opportunities: Research Grants - Visiting Researcher Grant - Brazil
• FAPESP's process: 18/18493-7 - Correlation between greenhouse gases, natural processes and land use in the Amazon Basin region
• Grantee: Graciela Tejada Pinell
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 11/51841-0 - UK/Brazil research network for an Amazonian Carbon Observatory
• Grantee: Luciana Vanni Gatti
• Support Opportunities: Research Program on Global Climate Change - Regular Grants
• FAPESP's process: 19/23654-2 - Estimation of Amazon greenhouse gas balances from atmospheric concentrations using inverse modelling of atmospheric transport with TOMCAT model
• Grantee: Luana Santamaria Basso
• Support Opportunities: Scholarships abroad - Research Internship - Post-doctor
• FAPESP's process: 16/02018-2 - Interannual variation of Amazon Basin greenhouse gas balances and their controls in a warming and increasingly variable climate – Carbam: the Amazon carbon balance long-term study
• Grantee: Luciana Vanni Gatti
• Support Opportunities: Research Program on Global Climate Change - Thematic Grants
• FAPESP's process: 20/02656-4 - Net carbon exchanges in the Amazon conciliating satellite data, ground data, and atmospheric profile in a decade of observation using bottom-up approach
• Grantee: Henrique Luis Godinho Cassol
• Support Opportunities: Scholarships abroad - Research Internship - Post-doctor