The limits to global-warming mitigation by terrestrial carbon removal
The limits to global-warming mitigation by terrestrial carbon removal
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DOI：
10.1002/2016ef000469
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发表时间：
2017-05-01
期刊：
影响因子：
8.2
通讯作者：
Schellnhuber, Hans Joachim
中科院分区：
文献类型：
--
作者：
Boysen, Lena R.;Lucht, Wolfgang;Schellnhuber, Hans Joachim
大规模的近期温室气体减排是《巴黎协定》所设想的将全球变暖保持在“远低于2摄氏度”的前提条件。此外，需要通过有管理的生物量增长以及随后的碳捕获和储存，广泛清除陆地二氧化碳，以避免在大多数相关情景中出现温度“超调”。在此，我们要解决两个主要问题：第一，我们要计算“修复”延迟或不充分的减排政策所需的tCDR的程度，这些政策无法防止全球平均气温比工业化前水平上升2.5摄氏度甚至4.5摄氏度。我们的研究结果表明，这些tCDR措施是无法抵消“一切照旧”的排放，而不消除几乎所有的自然生态系统。即使假设有相当大的减排量（代表性浓度途径4.5 [RCP 4.5]），50%储存效率的tCDR需要>1.1 Gha的最具生产力的农业区或消除> 50%的天然林。此外，在这些情景中，预计需要超过100 MtN/年的化肥才能去除大约320 GtC。这种干预将严重损害粮食生产和/或生物圈的功能。其次，我们重新分析了实现160-190 GtC tCDR的要求，这将补充强有力的减缓行动（RCP2.6），以避免任何时候2摄氏度的超调。我们发现，高灌溉水输入和/或更有效地转换为储存的碳的组合是必要的。面对社会和生物圈的严重权衡，我们得出结论，大规模tCDR不是积极减排的可行替代方案。然而，我们认为，如果立即建立可持续的计划，tCDR可能会成为强有力缓解的有价值的“支持者”。简明扼要的语言摘要2015年，缔约方同意将全球变暖限制在比工业化前水平高出“远低于”2摄氏度。然而，这不仅需要在近期大量减少温室气体排放，而且还需要应用“负排放”技术，从大气中提取已经排放的二氧化碳。具体而言，这可以指建立大面积种植速生树种和草种的种植园，同时将生物量转化为节碳产品。虽然这种部署被认为是有前途的，但其固碳潜力和可能的副作用仍有待深入研究。在这项研究中，我们分析了两个方面的可行性，这种负排放的方法，使用生物质种植园和碳利用途径。首先，我们表明，生物质种植园与随后的碳固定可能无法“修复”不充分的减排政策，而不损害粮食生产和生物圈功能，由于其空间消耗特性。其次，保持在2摄氏度目标以下的强缓解情景的要求将需要高灌溉水投入和开发高效的碳过程链相结合。虽然我们发现，这种固碳战略不是积极减排的可行替代方案，但如果可持续管理，它仍然可以支持减缓努力。
Massive near-term greenhouse gas emissions reduction is a precondition for staying "well below 2 degrees C" global warming as envisaged by the Paris Agreement. Furthermore, extensive terrestrial carbon dioxide removal (tCDR) through managed biomass growth and subsequent carbon capture and storage is required to avoid temperature "overshoot" in most pertinent scenarios. Here, we address two major issues: First, we calculate the extent of tCDR required to "repair" delayed or insufficient emissions reduction policies unable to prevent global mean temperature rise of 2.5 degrees C or even 4.5 degrees C above pre-industrial level. Our results show that those tCDR measures are unable to counteract "business-as-usual" emissions without eliminating virtually all natural ecosystems. Even if considerable (Representative Concentration Pathway 4.5 [RCP4.5]) emissions reductions are assumed, tCDR with 50% storage efficiency requires >1.1 Gha of the most productive agricultural areas or the elimination of > 50% of natural forests. In addition, > 100 MtN/yr fertilizers would be needed to remove the roughly 320 GtC foreseen in these scenarios. Such interventions would severely compromise food production and/or biosphere functioning. Second, we reanalyze the requirements for achieving the 160-190 GtC tCDR that would complement strong mitigation action (RCP2.6) in order to avoid 2 degrees C overshoot anytime. We find that a combination of high irrigation water input and/or more efficient conversion to stored carbon is necessary. In the face of severe trade-offs with society and the biosphere, we conclude that large-scale tCDR is not a viable alternative to aggressive emissions reduction. However, we argue that tCDR might serve as a valuable " supporting actor" for strong mitigation if sustainable schemes are established immediately.Plain Language Summary In 2015, parties agreed to limit global warming to " well below" 2 degrees C above pre-industrial levels. However, this requires not only massive near-term greenhouse gas emissions reductions but also the application of " negative emission" techniques that extract already emitted carbon dioxide from the atmosphere. Specifically, this could refer to the establishment of extensive plantations of fast-growing tree and grass species in combination with biomass conversion to carbon-saving products. Although such deployment is seen as promising, its carbon sequestration potentials and possible side-effects still remain to be studied in depth. In this study, we analyzed two feasibility aspects of such a negative emissions approach using biomass plantations and carbon utilization pathways. First, we show that biomass plantations with subsequent carbon immobilization are likely unable to "repair" insufficient emission reduction policies without compromising food production and biosphere functioning due to its space-consuming properties. Second, the requirements for a strong mitigation scenario staying below the 2 degrees C target would require a combination of high irrigation water input and development of highly effective carbon process chains. Although we find that this strategy of sequestering carbon is not a viable alternative to aggressive emission reductions, it could still support mitigation efforts if sustainably managed.