Department of Energy and Process Engineering, Norwegian University of Science and Technology (NTNU), 7491 Trondheim, Norway.
J Environ Manage. 2013 Nov 15;129:292-301. doi: 10.1016/j.jenvman.2013.07.021. Epub 2013 Aug 23.
Analyses of global warming impacts from forest bioenergy systems are usually conducted either at a single stand level or at a landscape level, yielding findings that are sometimes interpreted as contrasting. In this paper, we investigate and reconcile the scales at which environmental impact analyses of forest bioenergy systems are undertaken. Focusing on the changes caused in atmospheric CO2 concentration of forest bioenergy systems characterized by different initial states of the forest, we show the features of the analyses at different scales and depict the connections between them. Impacts on atmospheric CO2 concentration at a single stand level are computed through impulse response functions (IRF). Results at a landscape level are elaborated through direct application of IRFs to the emission profile, so to account for the fluxes from all the stands across time and space. Impacts from fossil CO2 emissions are used as a benchmark. At a landscape level, forest bioenergy causes an increase in atmospheric CO2 concentration for the first decades that is similar to the impact from fossil CO2, but then the dynamics clearly diverge because while the impact from fossil CO2 continues to rise that from bioenergy stabilizes at a certain level. These results perfectly align with those obtained at a single stand for which characterization factors have been developed. In the hypothetical case of a sudden cessation of emissions, the change caused in atmospheric CO2 concentration from biogenic CO2 emissions reverses within a couple of decades, while that caused by fossil CO2 emissions remains considerably higher for centuries. When counterfactual aspects like the additional sequestration that would have occurred in the forest if not harvested and the theoretical displacement of fossil CO2 are included in the analysis, results can widely differ, as the CO2 debt at a landscape level ranges from a few years to several centuries (depending on the underlying assumptions considered).
对森林生物能源系统的全球变暖影响的分析通常在单个林分水平或景观水平上进行，得出的结论有时被解释为相互矛盾的。在本文中，我们研究并协调了森林生物能源系统环境影响分析所采用的尺度。我们关注不同初始森林状态特征的森林生物能源系统中大气 CO2 浓度变化，展示了不同尺度分析的特点，并描绘了它们之间的联系。通过脉冲响应函数 (IRF) 计算单个林分水平上对大气 CO2 浓度的影响。通过直接将 IRF 应用于排放廓线来阐述景观水平上的结果，以便考虑跨越时间和空间的所有林分的通量。将化石 CO2 排放的影响作为基准。在景观水平上，森林生物能源在最初几十年会导致大气 CO2 浓度增加，这与化石 CO2 的影响相似，但随后动态明显分歧，因为虽然化石 CO2 的影响持续上升，但生物能源的影响稳定在一定水平。这些结果与为其开发特征因子的单个林分的结果完全一致。在假设的排放突然停止的情况下，由生物源 CO2 排放引起的大气 CO2 浓度变化在几十年内逆转，而由化石 CO2 排放引起的变化在几个世纪内仍保持较高水平。当包括额外的封存（如果不进行采伐，森林中可能会发生这种封存）和对化石 CO2 的理论替代等反事实方面时，结果可能会有很大差异，因为在景观水平上的 CO2 债务范围从几年到几百年（取决于所考虑的基本假设）。
