Carbon budgets for 1.5 and 2 °C targets lowered by natural wetland and permafrost feedbacks
Carbon budgets for 1.5 and 2 °C targets lowered by natural wetland and permafrost feedbacks
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DOI：
10.1038/s41561-018-0174-9
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发表时间：
2018-08-01
影响因子：
18.3
通讯作者：
Sitch, Stephen
中科院分区：
文献类型：
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作者：
Comyn-Platt, Edward;Hayman, Garry;Sitch, Stephen
全球天然湿地的甲烷排放和永久冻土融化的碳释放对气候有积极的反馈作用，但大多数最先进的气候模型都没有反映出来。此外，一部分融化的永久冻土碳以甲烷的形式释放，增强了综合反馈强度。我们提出了一个倒置的中间复杂性气候模型，它遵循规定的全球变暖途径，到2100年稳定在工业化前水平以上1.5或2.0摄氏度，并采用了最先进的全球陆地表面模型，更新了湿地和永久冻土碳释放的描述。我们证明了这两个过程的气候反馈是巨大的。具体而言，允许的人为化石燃料CO2排放预算在稳定在1.5摄氏度时减少17-23%（47-56 GtC），在稳定在2.0摄氏度时减少9-13%（52-57 GtC）。在我们的模拟中，这些反馈过程在低于1.5摄氏度的温度下响应更快，而1.5摄氏度和2摄氏度目标之间的差异不成比例地小。这一关键发现适用于到2100年的瞬态排放途径，并不能解释这些反馈过程的长期影响。我们的结论是，从湿地和永久冻土的自然反馈过程中必须考虑到瞬态排放途径的评估，以限制全球变暖。
Global methane emissions from natural wetlands and carbon release from permafrost thaw have a positive feedback on climate, yet are not represented in most state-of-the-art climate models. Furthermore, a fraction of the thawed permafrost carbon is released as methane, enhancing the combined feedback strength. We present simulations with an inverted intermediate complexity climate model, which follows prescribed global warming pathways to stabilization at 1.5 or 2.0 degrees C above pre-industrial levels by the year 2100, and which incorporates a state-of-the-art global land surface model with updated descriptions of wet-land and permafrost carbon release. We demonstrate that the climate feedbacks from those two processes are substantial. Specifically, permissible anthropogenic fossil fuel CO2 emission budgets are reduced by 17-23% (47-56 GtC) for stabilization at 1.5 degrees C, and 9-13% (52-57 GtC) for 2.0 degrees C stabilization. In our simulations these feedback processes respond more quickly at temperatures below 1.5 degrees C, and the differences between the 1.5 and 2 degrees C targets are disproportionately small. This key finding holds for transient emission pathways to 2100 and does not account for longer-term implications of these feedback processes. We conclude that natural feedback processes from wetlands and permafrost must be considered in assessments of transient emission pathways to limit global warming.