Brazil’s climate targets impaired by the potential cessation of the Amazon carbon sink

David M. Lapola, Jean P. Ometto, Giacomo Grassi, Ricardo V. Araújo, Marcio R. da Cruz, Adriane Esquivel-Muelbert, Marko S. Monteiro, Maíra C. G. Padgurschi

In accordance with the recommendations of the Intergovernmental Panel on Climate Change (IPCC), countries utilize the "managed land" proxy for their national greenhouse gas (GHG) emission inventories. This implies deducting “passive” carbon removals from countrywide gross GHG emissions. Long-term forest plots indicate that the carbon sink in structurally intact Amazon forest has weakened by roughly 30% since the 1990s, as CO₂-driven growth is increasingly offset by warming. This matters for accounting, given that the majority of the carbon removal reported by countries such as Brazil is passive uptake on managed land. That carbon sink is now being eroded by the same warming it is expected to help limit. Statistical extrapolation of that observational evidence indicate the Amazon carbon sink may cease by mid-2030s. Here we evaluate the impact of this potential cessation of the Amazon carbon sink in the mid-2030s on Brazil's future emissions, in the context of its Nationally Determined Contribution (NDC) to the Paris Agreement. This is achieved by rescaling the forest carbon removal term embedded within Brazil’s NDC target, which was determined with the support of an integrated-assessment model scenario. Our results indicate that the potential cessation of carbon removals by structurally intact Amazon forests will imply in an increase of 21% to 26% in Brazil's total (economy-wide) net emissions in 2035, in comparison with its NDC pledge. This finding may be relevant also for other regions, e.g. Africa, where comparable reductions in the carbon sink of their forests are also predicted to occur in the subsequent decades. It is crucial that Brazil and other forest nations that rely on currently strong passive sinks adjust their climate targets, for example by anticipating the timing of their net-zero pledge (currently set to 2050 in Brazil), and increasing its GHG emission cuts in sectors such as energy and transport.