Iordan Cristina-Maria, Hu Xiangping, Arvesen Anders, Kauppi Pekka, Cherubini Francesco
Industrial Ecology Programme, Department of Energy and Process Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.
Department of Environmental Sciences, University of Helsinki, Helsinki, Finland.
Carbon Balance Manag. 2018 Sep 4;13(1):12. doi: 10.1186/s13021-018-0101-9.
Forests and forest products can significantly contribute to climate change mitigation by stabilizing and even potentially decreasing the concentration of carbon dioxide (CO) in the atmosphere. Harvested wood products (HWP) represent a common widespread and cost-efficient opportunity for negative emissions. After harvest, a significant fraction of the wood remains stored in HWPs for a period that can vary from some months to many decades, whereas atmospheric carbon (C) is immediately sequestered by vegetation re-growth. This temporal mismatch between oxidation of HWPs and C uptake by vegetation generates a net sink that lasts over time. The role of temporary carbon storage in forest products has been analysed and debated in the scientific literature, but detailed bottom-up studies mapping the fate of harvested materials and quantifying the associated emission profiles at national scales are rare. In this work, we quantify the net CO emissions and the temporary carbon storage in forest products in Norway, Sweden and Finland for the period 1960-2015, and investigate their correlation. We use a Chi square probability distribution to model the oxidation rate of C over time in HWPs, taking into consideration specific half-lives of each category of products. We model the forest regrowth and estimate the time-distributed C removal. We also integrate the specific HWP flows with an emission inventory database to quantify the associated life-cycle emissions of fossil CO, CH and NO.
We find that assuming an instantaneous oxidation of HWPs would overestimate emissions of about 1.18 billion t CO (cumulative values for the three countries over the period 1960-2015).We also find that about 40 years after 1960, the starting year of our analysis, are sufficient to detect signs of negative emissions. The total amount of net CO emissions achieved in 2015 are about - 3.8 million t CO, - 27.9 t CO and - 43.6 t CO in Norway, Sweden, and Finland, respectively.
We argue for a more explicit accounting of the actual emission rates from HWPs in carbon balance studies and climate impact analysis of forestry systems and products, and a more transparent inclusion of the potential of HWP as negative emissions in perspective studies and scenarios. Simply assuming that all harvested carbon is instantaneously oxidized can lead to large biases and ultimately overlook the benefits of negative emissions of HWPs.
森林和林产品可通过稳定甚至潜在降低大气中二氧化碳（CO₂）浓度，对缓解气候变化做出重大贡献。采伐木制品（HWP）是实现负排放的常见、广泛且具有成本效益的机会。采伐后，很大一部分木材会在HWP中储存一段时间，储存期从几个月到几十年不等，而大气中的碳（C）会立即被植被再生长所固存。HWP氧化与植被碳吸收之间的这种时间错配产生了一个随时间持续的净碳汇。林产品中临时碳储存的作用已在科学文献中得到分析和讨论，但在国家层面详细的自下而上研究，绘制采伐材料的去向并量化相关排放概况的研究很少。在这项工作中，我们量化了1960 - 2015年期间挪威、瑞典和芬兰林产品中的净CO₂排放和临时碳储存，并研究它们之间的相关性。我们使用卡方概率分布来模拟HWP中碳随时间的氧化速率，同时考虑各类产品的特定半衰期。我们对森林再生长进行建模并估计随时间分布的碳清除量。我们还将特定的HWP流与排放清单数据库相结合，以量化化石CO₂、CH₄和NOₓ的相关生命周期排放。
我们发现，假设HWP瞬间氧化会高估约11.8亿吨CO₂的排放量（1960 - 2015年期间三个国家的累计值）。我们还发现，在我们分析的起始年份1960年后约40年，足以检测到负排放的迹象。2015年挪威、瑞典和芬兰实现的净CO₂排放总量分别约为 - 380万吨CO₂、 - 2790万吨CO₂和 - 4360万吨CO₂。
我们主张在林业系统和产品的碳平衡研究及气候影响分析中，更明确地核算HWP的实际排放率，并在远景研究和情景中更透明地纳入HWP作为负排放的潜力。简单地假设所有采伐的碳都瞬间氧化会导致巨大偏差，并最终忽视HWP负排放的益处。
