Abstract
Abstract. We summarise the contemporary carbon budget of South America and relate it to its dominant controls: population and economic growth, changes in land use practices and a changing atmospheric environment and climate. Component flux estimate methods we consider sufficiently reliable for this purpose encompass fossil fuel emission inventories, biometric analysis of old-growth rainforests, estimation of carbon release associated with deforestation based on remote sensing and inventories, and agricultural export data. Alternative methods for the estimation of the continental-scale net land to atmosphere CO2 flux, such as atmospheric transport inverse modelling and terrestrial biosphere model predictions, are, we find, hampered by the data paucity, and improved parameterisation and validation exercises are required before reliable estimates can be obtained. From our analysis of available data, we suggest that South America was a net source to the atmosphere during the 1980s (~ 0.3–0.4 Pg C a−1) and close to neutral (~ 0.1 Pg C a−1) in the 1990s. During the latter period, carbon uptake in old-growth forests nearly compensated for the carbon release associated with fossil fuel burning and deforestation. Annual mean precipitation over tropical South America as inferred from Amazon River discharge shows a long-term upward trend. Although, over the last decade dry seasons have tended to be drier, with the years 2005 and 2010 in particular experiencing strong droughts. On the other hand, precipitation during the wet seasons also shows an increasing trend. Air temperatures have also increased slightly. Also with increases in atmospheric CO2 concentrations, it is currently unclear what effect these climate changes are having on the forest carbon balance of the region. Current indications are that the forests of the Amazon Basin have acted as a substantial long-term carbon sink, but with the most recent measurements suggesting that this sink may be weakening. Economic development of the tropical regions of the continent is advancing steadily, with exports of agricultural products being an important driver and witnessing a strong upturn over the last decade.
Highlights
This review of the carbon balance of South America, with an emphasis on trends over the last few decades and their determinants, forms part of a catalogue of similar regional syntheses covering the globe as part of the RECCAP (REgional Carbon Cycle Assessment and Processes) effort
Component flux estimate methods we consider sufficiently reliable for this purpose encompass fossil fuel emission inventories, biometric analysis of old-growth rainforests, estimation of carbon release associated with deforestation based on remote sensing and inventories, and agricultural export data
The scope of our analyses encompasses all methodologies as prescribed by RECCAP, including a “bottom-up” estimation of the net carbon balance through the assimilation of component flux measurements, simulations with Dynamic Global Vegetation Models (DGVMs) and atmospheric transport inversions
Summary
This review of the carbon balance of South America, with an emphasis on trends over the last few decades and their determinants, forms part of a catalogue of similar regional syntheses covering the globe as part of the RECCAP (REgional Carbon Cycle Assessment and Processes) effort. Drought induced forest loss may be further amplified by fire (White et al, 1999; Cox et al, 2000; Poulter et al, 2010; Nepstad et al, 1999; Aragao and Shimabukuro, 2010) It is the interplay between the very large area covered by high carbon density and relatively undisturbed forests with the very fast economic and demographic development, and these interacting with a changing climate, which makes South America of particular interest for its role in the contemporary carbon cycle and, in turn, to the climate of the planet over the decades to come. Improved access to global markets has played an important role in this development, especially over recent years (e.g. Nepstad et al, 2006a; DeFries, 2010, Butler and Laurance, 2008; Finer and Orta-Martinez, 2010)
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