Does replacing coal with wood lower CO 2 emissions? Dynamic lifecycle analysis of wood bioenergy
Does replacing coal with wood lower CO 2 emissions? Dynamic lifecycle analysis of wood bioenergy
复制标题
用木材代替煤炭会降低 CO 2 排放吗？
DOI：
10.1088/1748-9326/aaa512
复制
发表时间：
2017
影响因子：
6.7
通讯作者：
Rooney-Varga, Juliette N
中科院分区：
文献类型：
--
作者：
Sterman, John D;Siegel, Lori;Rooney-Varga, Juliette N
随着各国寻求减少温室气体排放，生物能源正在蓬勃发展。欧盟宣布生物燃料是碳中性的，引发了木材使用的激增。但生物燃料真的能减少排放吗？今天排放的一个二氧化碳分子对辐射强迫的影响是相同的，无论它来自煤炭还是生物质。随着时间的推移，生物燃料只能通过收获后净初级生产（NPP）的增加来减少大气中的CO2。因此，生物燃料对气候的影响取决于生物燃料与化石燃料燃烧产生的二氧化碳排放量、收获土地的命运和NPP的动态。在这里，我们开发了一个动态的生物能源生命周期分析模型。该模型跟踪大气、生物量和土壤之间的碳储量和通量，可扩展到多种土地类型和地区，运行时间为100秒，能够进行快速、互动的政策设计和敏感性测试。我们模拟替代煤炭发电的木材，估计NPP和其他通量使用的数据在美国东部的森林和使用已公布的估计供应链排放的参数。由于木材的燃烧和加工效率低于煤炭，以木材替代煤炭的直接影响是大气中二氧化碳相对于煤炭的增加。这种碳债务的偿还期在砍伐后的44-104年之间，这取决于森林类型假设土地仍然是森林。令人惊讶的是，用快速生长的松树种植园重新种植硬木林会增加木材的二氧化碳影响，因为种植园的平衡碳密度低于天然林。此外，由于新的碳债务不断超过NPP，预计生物能源木材采伐量的增长将增加大气中的CO 2至少世纪。假设生物燃料是碳中和的，可能会在利益积累之前加剧气候变化的不可逆转的影响。相反，应该使用明确的动态模型来评估生物燃料的气候影响。
Bioenergy is booming as nations seek to cut their greenhouse gas emissions. The European Union declared biofuels to be carbon-neutral, triggering a surge in wood use. But do biofuels actually reduce emissions? A molecule of CO 2 emitted today has the same impact on radiative forcing whether it comes from coal or biomass. Biofuels can only reduce atmospheric CO 2 over time through post-harvest increases in net primary production (NPP). The climate impact of biofuels therefore depends on CO 2 emissions from combustion of biofuels versus fossil fuels, the fate of the harvested land and dynamics of NPP. Here we develop a model for dynamic bioenergy lifecycle analysis. The model tracks carbon stocks and fluxes among the atmosphere, biomass, and soils, is extensible to multiple land types and regions, and runs in≈ 1s, enabling rapid, interactive policy design and sensitivity testing. We simulate substitution of wood for coal in power generation, estimating the parameters governing NPP and other fluxes using data for forests in the eastern US and using published estimates for supply chain emissions. Because combustion and processing efficiencies for wood are less than coal, the immediate impact of substituting wood for coal is an increase in atmospheric CO 2 relative to coal. The payback time for this carbon debt ranges from 44–104 years after clearcut, depending on forest type—assuming the land remains forest. Surprisingly, replanting hardwood forests with fast-growing pine plantations raises the CO 2 impact of wood because the equilibrium carbon density of plantations is lower than natural forests. Further, projected growth in wood harvest for bioenergy would increase atmospheric CO 2 for at least a century because new carbon debt continuously exceeds NPP. Assuming biofuels are carbon neutral may worsen irreversible impacts of climate change before benefits accrue. Instead, explicit dynamic models should be used to assess the climate impacts of biofuels.