A changing Amazon rainforest: Historical trends and future projections under post-Paris climate scenarios

摘要

Despite the progress in sustainable development strategies, the role of the Amazon rainforest as a carbon sink faces increasing disturbances that may have a critical impact on global climate. Understanding the vulnerability of the Amazon rainforest to climate change is a major challenge, considering the complex interaction between human and natural systems. This paper aims, via an interdisciplinary approach, to assess the observed evolution and possible future of the Amazon rainforest, considering different global climate and socioeconomic scenarios. By comparing historical with plausible future developments, we present key knowledge to inform mitigation and regional adaptation policy considerations. As an entry point, historical trends of annual mean temperature and precipitation were analysed. In a second step, the same assessment was made for the mean annual NDVI sum (a proxy of yearly plant productivity), representing vegetation strength. For these purposes, a 34-year period (1982-2015) was considered. Trends were analysed based on non-parametric Mann-Kendall and Sen's methods. With this representation of the past, the next step focused on future scenarios. The most plausible global emission pathways were evaluated via the comparison of ten assessments of the possible effects of the mitigation action plans of national governments, as stated in the National Determined Contributions (NDCs). Results indicate a strong consensus that if either current policies, unconditional or conditional NDCs are fulfilled, the limit of global warming by "well below 2 degrees C" will be exceeded. In this context, climate projections for the Amazon suggest, among other results, an increase in the range of 1.3 degrees C (lower limit under SSP1-2.6) to 6.5 degrees C (upper limit under SSP5-8.5). Unlike temperature, positive and negative anomalies are expected for precipitation depending on location. Despite the uncertainty regarding the projections, possible changes such as forest diebacks and sav-annization may take place, namely in southeastern Amazon, by the end of the century. Overall, this study highlights the importance of carefully considering the combination of different factors, such as deforestation, to guarantee rainforest resilience under climate-driven changes.