Brazil is experiencing a sharp decline in environmental protection policies since its change of government in 2019. However, no study has yet quantified the impact of this event on the country's carbon stocks.

The Amazonian rainforest, of which more than 60% is located in Brazil, is undergoing multiple degradations due to human activities and climatic hazards. Consequently, areas located on the edge of deforested regions are weakened while others are affected by occasional tree felling or fires. Moreover, drought increases tree mortality and promotes the loss of branches and leaves.

While deforestation can be monitored using satellite images, other forest degradations are much more difficult to observe. Nevertheless, it is possible to assess their impact on forest biomass with the L-VOD satellite vegetation index, developed by researchers from the INRAE, the CEA and the CNRS. Using this index, as well as a new deforestation monitoring technique developed by the University of Oklahoma, the collaboration was able to determine the evolution in the Brazilian Amazon rainforest's carbon stock between 2010 and 2019.

The study highlights a clear increase in deforestation in 2019 (3.9 million hectares). This is 30% higher than what was observed in 2015 during the extreme El Niño drought (3 million hectares), and represents a fourfold increase compared to 2017 and 2018 (1 million hectares).

However, when other forest degradations are taken into account, it turns out that forest carbon losses were three times higher in 2015 than in 2019! This result underlines the crucial role of climate, which during the 2015 El Niño dry event affected the forest very strongly with increased tree mortality and degradation caused by fires.

Overall, the researchers observed a reversal of the historical trend in the Brazilian rainforest's carbon storage role. Indeed, from 2010 to 2019, the Brazilian Amazon rainforest lost 1% of its carbon stock, mainly due to forest degradation (excluding deforestation) – the impact of which is three times greater than that of deforestation.

Environmental protection policies should therefore take into account the degradation of forests as a whole (and not just deforestation), in order to preserve the carbon storage capacity of forests, a crucial component of climate change mitigation.