Center for Meteorological and Climatic Research Applied to Agriculture, University of Campinas, 13083-886 Campinas, SP, Brazil;
Stockholm Resilience Center, Stockholm University, 11419 Stockholm, Sweden.
Proc Natl Acad Sci U S A. 2018 Nov 13;115(46):11671-11679. doi: 10.1073/pnas.1721770115. Epub 2018 Nov 5.
Large uncertainties still dominate the hypothesis of an abrupt large-scale shift of the Amazon forest caused by climate change [Amazonian forest dieback (AFD)] even though observational evidence shows the forest and regional climate changing. Here, we assess whether mitigation or adaptation action should be taken now, later, or not at all in light of such uncertainties. No action/later action would result in major social impacts that may influence migration to large Amazonian cities through a causal chain of climate change and forest degradation leading to lower river-water levels that affect transportation, food security, and health. Net-present value socioeconomic damage over a 30-year period after AFD is estimated between US dollar (USD) $957 billion (×10) and $3,589 billion (compared with Gross Brazilian Amazon Product of USD $150 billion per year), arising primarily from changes in the provision of ecosystem services. Costs of acting now would be one to two orders of magnitude lower than economic damages. However, while AFD mitigation alternatives-e.g., curbing deforestation-are attainable (USD $64 billion), their efficacy in achieving a forest resilience that prevents AFD is uncertain. Concurrently, a proposed set of 20 adaptation measures is also attainable (USD $122 billion) and could bring benefits even if AFD never occurs. An interdisciplinary research agenda to fill lingering knowledge gaps and constrain the risk of AFD should focus on developing sound experimental and modeling evidence regarding its likelihood, integrated with socioeconomic assessments to anticipate its impacts and evaluate the feasibility and efficacy of mitigation/adaptation options.
尽管观测证据表明森林和区域气候正在发生变化，但由于存在很大的不确定性，亚马逊森林大面积死亡（AFD）这一假说仍难以确定，即气候变化是否会导致亚马逊森林发生大规模突然转变。本文旨在评估在这种不确定性下，现在、以后或根本不采取缓解或适应措施的情况下会产生何种后果。不采取行动/以后采取行动会导致重大的社会影响，可能会通过气候变化和森林退化导致的河水水位下降影响交通、粮食安全和健康，从而引发向大型亚马逊城市的移民，从而产生因果链。AFD 后 30 年内的社会经济净现值损害估计在 9570 亿美元（×10）至 35890 亿美元（与巴西亚马逊每年 1500 亿美元的总生产总值相比）之间，主要源于生态系统服务提供的变化。现在采取行动的成本要低一到两个数量级，而经济损失则要高得多。然而，虽然实现 AFD 缓解的替代方案（例如，遏制森林砍伐）是可行的（640 亿美元），但它们在实现防止 AFD 的森林恢复能力方面的效果尚不确定。同时，还可以采取一整套 20 项适应措施（1220 亿美元），即使 AFD 从未发生，也能带来好处。一个跨学科的研究议程，以填补尚存的知识空白并限制 AFD 的风险，应侧重于开发有关其可能性的可靠实验和建模证据，同时与社会经济评估相结合，以预测其影响，并评估缓解/适应方案的可行性和效果。
