<p>After a period where atmospheric methane (CH<sub>4</sub>) levels were nearly steady, its levels have been rapidly raising since 2007, but the main reasons remains uncertain. Increases in wetlands emissions could be one possible reason, mainly at tropical regions like Amazonia, which host some of the largest wetlands/seasonally flooded areas on the globe. Based on 590 lower troposphere vertical profiles of CH<sub>4</sub> and carbon monoxide (CO) observations over four sites at Amazon (at the northeast, southeast, northwest-central and southwest-central regions) we estimated that Amazon region contributes with 8% of global CH<sub>4</sub> emissions, and wetlands are the mainly CH<sub>4</sub> source to the atmosphere (Basso et al., 2021). Vertical profiles are sampled using light aircraft, high-precision greenhouse gas and CO analysis of flask air, fortnightly between 2010 and 2018. We observed an unexpected east-west gradient in CH<sub>4</sub> emissions, with higher emissions in northeast Amazon region. The higher emissions are mainly from wetlands and are not explained by biomass burning and anthropogenic emissions (like enteric fermentation), but its causes remains unclear. In the other three sites located further downwind along the main air-stream the CH<sub>4</sub> emissions represents approximately 24-36% of what is observed in the northeast region. Our wetlands emission estimates of each region were compared to analogous fluxes from the WetCharts wetland model ensemble (Bloom et al., 2017). The estimates were similar except for the northeast region, where WetCharts does show substantial emissions, but still just 40% of our estimates based on the lower troposphere observations (Basso et al., 2021).</p>
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.
The Amazon Forest is a major locus for carbon and water cycling in the climate system whose function has been degraded in recent decades by land use and climate change. Most studies of Amazonia’s carbon balance have been limited by sparse sampling. We measured 742 atmospheric vertical profiles of CO2 and CO over four regions of Amazonia from 2010 through 2020. We estimate that Amazon carbon emissions increased from 0.24±0.19 PgC y-1 in 2010-18 to 0.44±0.22 in 2019 and 0.52±0.22 PgC y-1 in 2020. During these years, increases were also observed in deforestation (79% and 74%) and forest burned area (14% and 42%). Field notifications for illegal deforestation and related crimes dropped by 42%, while fines paid for judgments held fell by 89%. Carbon losses during 2019 and 2020 were comparable to losses in the record warm El Nino event of 2015-16, but this time with usual to moderate Oceanic Ninõ Index. 2020 showed 12% decrease in precipitation indicating also a climate impact in carbon emissions. The changes during 2019 and 2020 were mainly due to the western Amazonia becoming also a carbon source. We hypothesize that the consequences of the collapse in enforcement led to increase in deforestation, biomass burning and degradation producing net carbon losses and enhancing drying and warming of forest regions.
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