Holocene peatland and ice-core data constraints on the timing and magnitude of CO2 emissions from past land use
Holocene peatland and ice-core data constraints on the timing and magnitude of CO2 emissions from past land use
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DOI：
10.1073/pnas.1613889114
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发表时间：
2017-01
期刊：
影响因子：
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通讯作者：
B. Stocker;Zicheng Yu;C. Massa;F. Joos
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文献类型：
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作者：
B. Stocker;Zicheng Yu;C. Massa;F. Joos
意义 工业化前农业扩张的时间、范围和影响尚不确定，但对于理解人类在地球环境历史中的作用至关重要。冰河时代之后开始的北部泥炭地的形成是一个主要的碳汇，如果时间匹配的话，可以补偿土地利用带来的大量二氧化碳排放。我们根据所有已发布的情景，对过去的泥炭地碳和土地利用二氧化碳排放量进行了基于观测和模型的重建。我们对陆地碳平衡的分析揭示了在全新世中期气候最适期之后存在大量非泥炭地碳源，这不能用土地利用来解释，而且我们发现先前提出的二氧化碳与人口和土地利用历史之间的联系并不得到支持。工业化前土地利用变化（LUC）造成的二氧化碳排放存在很大的不确定性。尽管大气二氧化碳记录表明自 5000 年前 (5 kyBP) 以来只有少量陆地碳 (C) 来源，但泥炭堆积造成的并发碳汇可能掩盖大量早期 LUC 排放。在这里，我们将更新的连续泥炭碳重建与不同时间尺度的大气 CO2 和 δ13C 的双重反褶积分析推断出的土地碳平衡相结合，以研究全新世和上千年的陆地碳收支并限制 LUC 排放。 LUC 排放量是通过瞬态模型模拟估算的，针对不同已发布的土地利用面积变化和轮耕情景。我们的结果揭示了全新世中期之后存在大量陆地非泥炭地碳源（7-5 kyBP 时为 66 ± 25 PgC，5-3 kyBP 时为 115 ± 27 PgC）。尽管在农业发展的早期阶段，土地利用和土地利用的模拟人均二氧化碳排放量很高，但人类只是在最近三千年才成为对全球碳循环产生主导影响的驱动因素。不支持 CO2 记录中特定变化的唯一人为原因（7 kyBP 后上升约 20 ppm，公元 1500 年至 1600 年期间下降约 10 ppm）。该分析对工业前与工业时代的 LUC 排放进行了严格限制，并表明公元 1850 年之前农业扩张程度的高端情景与此后的碳预算不兼容。
Significance Timing, extent, and impacts of preindustrial agricultural expansion are uncertain, yet crucial for understanding the role of humans in the Earth’s environmental history. The buildup of northern peatlands, initiated after ice-age conditions, was a major carbon sink and could have compensated large CO2 emissions from land use, given timing matches. We present observation- and model-based reconstructions of past peatland carbon and land-use CO2 emission estimates based on all published scenarios. Our analyses of the terrestrial carbon balance reveal a large nonpeatland land carbon source after the Mid-Holocene climate optimum, not explained by land use, and we find that previously suggested links between CO2 and population and land-use history are not supported. CO2 emissions from preindustrial land-use change (LUC) are subject to large uncertainties. Although atmospheric CO2 records suggest only a small land carbon (C) source since 5,000 y before present (5 kyBP), the concurrent C sink by peat buildup could mask large early LUC emissions. Here, we combine updated continuous peat C reconstructions with the land C balance inferred from double deconvolution analyses of atmospheric CO2 and δ13C at different temporal scales to investigate the terrestrial C budget of the Holocene and the last millennium and constrain LUC emissions. LUC emissions are estimated with transient model simulations for diverging published scenarios of LU area change and shifting cultivation. Our results reveal a large terrestrial nonpeatland C source after the Mid-Holocene (66 ± 25 PgC at 7–5 kyBP and 115 ± 27 PgC at 5–3 kyBP). Despite high simulated per-capita CO2 emissions from LUC in early phases of agricultural development, humans emerge as a driver with dominant global C cycle impacts only in the most recent three millennia. Sole anthropogenic causes for particular variations in the CO2 record (∼20 ppm rise after 7 kyBP and ∼10 ppm fall between 1500 CE and 1600 CE) are not supported. This analysis puts a strong constraint on preindustrial vs. industrial-era LUC emissions and suggests that upper-end scenarios for the extent of agricultural expansion before 1850 CE are not compatible with the C budget thereafter.