The carbon balance of South America: a review of the status, decadal trends and main determinants

[摘要] We summarise the contemporary carbon budget of South America and relate itto its dominant controls: population and economic growth, changes in landuse practices and a changing atmospheric environment and climate. Componentflux estimate methods we consider sufficiently reliable for this purposeencompass fossil fuel emission inventories, biometric analysis of old-growthrainforests, estimation of carbon release associated with deforestationbased 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 modellingand terrestrial biosphere model predictions, are, we find, hampered by the datapaucity, and improved parameterisation and validation exercises are requiredbefore reliable estimates can be obtained. From our analysis of availabledata, we suggest that South America was a net source to the atmosphere duringthe 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 carbonrelease associated with fossil fuel burning and deforestation.

Annual mean precipitation over tropical South America as inferred fromAmazon River discharge shows a long-term upward trend. Although, over thelast decade dry seasons have tended to be drier, with the years 2005 and2010 in particular experiencing strong droughts. On the other hand,precipitation during the wet seasons also shows an increasing trend. Airtemperatures have also increased slightly. Also with increases inatmospheric CO₂ concentrations, it is currently unclear what effectthese 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 asubstantial long-term carbon sink, but with the most recent measurementssuggesting that this sink may be weakening. Economic development of thetropical regions of the continent is advancing steadily, with exports ofagricultural products being an important driver and witnessing a strongupturn over the last decade.

[学科分类] 地球化学与岩石