Comment on egusphere-2023-19

Abstract

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-σ 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.

Authors 11

1. Luana S. Basso corresponding

   University of Leeds · Instituto Nacional de Pesquisas Espaciais

   Affiliation as printed

   General Coordination of Earth Science (CGCT), National Institute for Space Research (INPE), São José dos Campos, Brazil

   School of Geography, University of Leeds, Leeds, LS2 9JT, UK

2. Chris Wilson corresponding

   University of Leeds · National Centre for Earth Observation

   Affiliation as printed

   National Centre for Earth Observation, University of Leeds, Leeds, LS2 9JT, UK

   School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK

3. Martyn P. Chipperfield corresponding

   University of Leeds · National Centre for Earth Observation

   Affiliation as printed

   National Centre for Earth Observation, University of Leeds, Leeds, LS2 9JT, UK

   School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK

4. Graciela Tejada corresponding

   Instituto Nacional de Pesquisas Espaciais

   Affiliation as printed

   General Coordination of Earth Science (CGCT), National Institute for Space Research (INPE), São José dos Campos, Brazil

5. Henrique Cassol corresponding

   National Centre for Earth Observation · Instituto Nacional de Pesquisas Espaciais · University of Edinburgh

   Affiliation as printed

   General Coordination of Earth Science (CGCT), National Institute for Space Research (INPE), São José dos Campos, Brazil

   School of GeoSciences & National Centre for Earth Observation, University of Edinburgh, UK

6. Egídio Arai corresponding

   Instituto Nacional de Pesquisas Espaciais

   Affiliation as printed

   General Coordination of Earth Science (CGCT), National Institute for Space Research (INPE), São José dos Campos, Brazil

7. T. Luke Smallman corresponding

   National Centre for Earth Observation · University of Edinburgh

   Affiliation as printed

   School of GeoSciences & National Centre for Earth Observation, University of Edinburgh, UK

8. Wouter Peters corresponding

   University of Groningen · Wageningen University & Research

   Affiliation as printed

   University of Groningen, Centre for Isotope Research, Groningen, The Netherlands

   Wageningen University, Environmental Sciences Group, 6708PB, Wageningen, The Netherlands

9. Stijn Naus corresponding Aachen SRON Netherlands Institute for Space Research

   Space Research Organisation Netherlands · Wageningen University & Research

   Affiliation as printed

   Meteorology and Air Quality, Wageningen University and Research, The Netherlands

   SRON Netherlands Institute for Space Research, Utrecht, The Netherlands

10. John Bharat Miller corresponding

    National Oceanic and Atmospheric Administration · NOAA Global Monitoring Laboratory

    Affiliation as printed

    NOAA – Global Monitoring Laboratory, Boulder, Colorado 80305, USA

11. Manuel U. Gloor corresponding

    University of Leeds

    Affiliation as printed

    School of Geography, University of Leeds, Leeds, LS2 9JT, UK