Abstract
Since the 1960s, large-scale deforestation in the Amazon Basin has contributed to rising global CO2 concentrations and to climate change. Recent advances in satellite observations enable estimates of gross losses of above-ground biomass (AGB) stocks due to deforestation. However, because of simultaneous regrowth, the net contribution of deforestation emissions to rising atmospheric CO2 concentrations is poorly quantified. Climate change may also reduce the potential for forest regeneration in previously disturbed regions. Here, we address these points of uncertainty with a machine-learning approach that combines satellite observations of AGB with climate data across the Amazon Basin to reconstruct annual maps of potential AGB during 1993–2012, the above-ground C storage potential of the undisturbed landscape. We derive a 2.2 Pg C loss of AGB over the study period, and, for the regions where these losses occur, we estimate a 0.7 Pg C reduction in potential AGB. Thus, climate change has led to a decline of ~1/3 in the capacity of these disturbed forests to recover and recapture the C lost in disturbances during 1993–2012. Our approach further shows that annual variations in land use change mask the natural relationship between the El Niño/Southern Oscillation and AGB stocks in disturbed regions.
Highlights
The terrestrial carbon sink helps offset about 25% of anthropogenic emissions of fossil-fuel responsible for climate change[1,2]
AGBdef continuously evolves through time as it is the difference between AGBpot, which is only driven by climate and atmospheric CO2 concentrations, and AGBobs which is driven by land use activities as well as climate and atmospheric CO2 concentrations
The stabilisation of AGBdef after 2005 is associated to a reduction of AGBobs loss rate from 0.17 Pg C y−1 to 0.04 Pg C y−1 before and after 2005 respectively (Fig. 2). It corresponds to a reduction in deforestation rates over the Brazilian Amazon seen in data from INPE (Figure S1 in the Supplementary Information; r = 0.97; p ≪ 0.001) while the smooth decreases of AGBpot throughout the study period indicates a long-term negative impact of climate on the regeneration potential of disturbed regions (Fig. 2)
Summary
The terrestrial carbon sink helps offset about 25% of anthropogenic emissions of fossil-fuel responsible for climate change[1,2]. The extent of land cover change in the Amazon Basin can be quantified with some degrees of confidence using satellite-based observations[3] Merging these observations with maps[4,5] of Aboveground Biomass Carbon (AGB) provides a baseline estimation of gross losses from deforestation[6]. A way to address these problems is to study the deviation of current AGB stocks from potential stocks, to determine and separate the human-induced and climate-induced biomass deficits These potential stocks are those that would exist under current climate if previous large-scale deforestation and degradation had not occurred (potential AGB further noted as AGBpot[8]; see Methods). We aim to answer the following questions:
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