Large and increasing methane emissions from Eastern Amazonia derived from satellite data, 2010–2018

Abstract. We use a global inverse model, satellite data and flask measurements to estimate methane (CH₄) emissions from South America, Brazil and the basin of the Amazon River for the period 2010–2018. We find that emissions from Brazil have risen during this period, most quickly in the Eastern Amazon Basin, and that this concurrent with increasing surface temperatures in this region. Brazilian CH₄ emissions rose from 49.8 ± 5.4 Tg(CH₄)/yr in 2010–2013 to 55.6 ± 5.2 Tg(CH₄)/yr in 2014–2017, with the wet season of December–March having the largest positive trend in emissions. We derive no significant trend in regional emissions from fossil fuels during this period. We find that our posterior distribution of emissions within South America is significantly and consistently changed from our prior estimates, with the strongest emission sources being in the far north of the continent and to the south and south-east of the Amazon Basin, near the mouth of the Amazon and in other wetland regions. We derive particularly large emissions during the wet season of 2013/14, when flooding was prevalent over larger regions than normal within the Amazon Basin. We compare our posterior CH₄ mole fractions, derived from posterior fluxes, to independent observations of CH₄ mole fraction taken at five lower to mid tropospheric vertical profiling sites over the Amazon and find that our posterior fluxes outperform prior fluxes at all locations. In particular the large emissions from the eastern Basin are shown to be in good agreement with independent observations made at Santarém, a location which has long displayed higher mole fractions of atmospheric CH₄ in contrast with other Basin locations. We show that a bottom-up flux model cannot match the variation in annual fluxes, nor the positive trend in emissions, produced by the inversion. Our results show that the Amazon alone was responsible for 24 ± 18 % of the total global increase in CH₄ flux during the study period, and it may contribute further in future due to its sensitivity to temperature changes.