长期生物碳储存

请注意，这是一个相当高级的主题. 有关生物碳的介绍，请从以下文章开始: 计算木制品中的碳储量, 何时在LCA中加入生物碳, 如何将生物碳纳入LCA , WBLCA工具中的生物碳核算.

在它们的生命周期中, wood products store biogenic carbon that was sequestered from the atmosp在这里 by trees during their growth. 在建筑物使用寿命结束时, 木制品有许多使用寿命结束的情况, 它们储存的生物碳的命运各不相同:

• 当材料被重复使用或回收时, the biogenic carbon leaves the current product system and is transferred to the next product or building.
• 用于能量回收的焚烧产生脉冲发射.
• Landfilling results in the slow release of emissions over time (due to partial decomposition), 而一部分生物碳则永久储存在地下.

在所有情况下, 在木制品的生命周期开始时，有一个生物碳去除过程, t在这里 might be a partial or complete biogenic carbon emission at the end of the life cycle. T在这里 might also be biogenic carbon removals and emissions throughout the life cycle, 这些都在 第2部分, but the majority of biogenic carbon flows occur near the beginning and the end of the product’s life.

第1部分 本系列讨论了如何报道生物碳流, 使用“-1输入/+1输出”的方法, 符合ISO 21390标准. This is a static approach to including biogenic carbon in a life cycle assessment (LCA) and assumes biogenic carbon removals (carbon uptake in the forest) occur at the same point in time as carbon emissions. 作为一个简化的例子, 假设你有一个可以储存1,在其木制品中减少了000公斤的生物碳. 100年后, 在这栋楼的寿命结束时, 假设所有储存的生物碳都被释放回大气. 在这种情况下，你的 网 biogenic carbon flows are zero (-1,000 kg into the system, +1,000 kg out of the system).¹

然而，这种方法忽略了这些清除和排放的时间. 我们知道CO₂ 寿命长(i.e., residence time) in the atmosp在这里; once it is emitted, 它存在于大气中，从300到1,000年.² 每年CO₂ 存在于大气中，它具有变暖效应，称为 辐射强迫. 图1显示了脉冲输入1000kg CO时的辐射强迫曲线₂ 在时刻0发射. 这种排放最初具有很大的年变暖影响(例如.e.，辐射强迫). 随着时间的推移，一些CO₂ is absorbed by the biosp在这里—oceans and plant life on Earth—which decreases its annual warming impact. 然而, 即使在100年, the portion of the original emission that remains in the atmosp在这里 continues to have a significant warming effect.

图1:每年1,000公斤二氧化碳的变暖影响₂

在大气层中停留的时间 总计 CO增温效应₂ 被称为 累积辐射强迫. When calculating potential global warming impacts over an assumed period of time (e.g.， 100年)，累积辐射强迫表明1000 kg CO₂ emitted to the atmosp在这里 today has a higher 总计 global warming potential (GWP) than 1,000公斤一氧化碳₂ 50年排放量. This is demonstrated in Figure 2 w在这里 the 辐射强迫 curve from Figure 1 (blue) is overlaid with the 辐射强迫 curve for 1,000公斤一氧化碳₂ 在第50年发出(橙色). 阴影区域表示 累积辐射强迫 (或总变暖效应). The difference between these two areas is the 总计 warming impact that can be avoided by delaying the emission by 50 years. (在这种情况下, the area in blue is about 73% larger than the area in orange indicating that over a 100-year timeframe, 一个公司₂ emission now will have 73% more warming impact than an emission that’s delayed by 50 years.)

图2:1,000公斤二氧化碳的累积变暖影响₂ 在不同的时间

In the context of whole building life cycle assessment (WBLCA) w在这里 we typically look at a building life of 60 to 100 years, 很明显，在生产阶段发生的排放(A1-A3), 接近生命周期的开始, can have much greater impacts than emissions that happen at the end-of-life stage (C1-C4).³

同样，去除1000公斤的一氧化碳₂ from the atmosp在这里 today has climate change mitigation benefits over removing 1,000公斤一氧化碳₂ 50年后. 换句话说, 由于早期的碳去除，木材具有额外的气候效益, long-term carbon storage and delayed carbon emissions that are typically excluded from a traditional static LCA approach.

This has been an area of study among scientists for some time—and several methods have been proposed that consider the timing of removals and emissions, 以及相关的气候影响. 由于在标准化计算方法上缺乏国际共识, ISO 21930 does not currently allow for the climate impacts associated with long-term carbon storage and delayed emissions to be quantified and reported as part of the GWP impact indicator. 然而, it does permit this quantitative or qualitative information to be reported under a category called, "非来自LCA的额外环境信息.” ⁴

To maintain alignment with current ISO standards, we recommend reporting the amount of 储存在木制品中的生物碳 分别. Keeping a record of this carbon storage allows us to quantify the potential future benefits—for example, biogenic carbon that will continue to be stored if the building’s life is extended or the wood products are reused. It is important to understand and document the amount of carbon that will be withheld from the atmosp在这里 for the life of the building or longer. It is possible that future versions of international standards might include updated quantification methods that will allow for designers to account for the climate benefits associated with long-term carbon storage and delayed emission in the reporting of GWP for wood buildings.

额外的资源:

CIRAIG. 5月(2010). dynCO2:动态碳足迹.

国际标准化组织. (2017). ISO 21930:2017 可持续性 in buildings and civil engineering works – Core rules for environmental product declarations of construction products and services.

Levasseur,.等。. (2010). Considering Time in LCA: Dynamic LCA and Its Application to Global Warming Impact Assessments. 环境科学 & 技术.

斯鲁巴三世，W.等。. (2021). Aureus Earth公司. 基于建筑的隐含碳补偿方法.

莫拉·科斯塔，医学博士.威尔逊，C. (1999). CO之间的等效系数₂ 避免排放和封存-描述及其在林业中的应用. 减缓和适应全球变化战略.

¹ 为简单起见, this example ignores any biogenic carbon flows that might happen during the operational stage of the building’s life and realistic end-of-life scenarios like permanent sequestration in a landfill or reuse/recycling w在这里 some or all of the carbon may never return to the atmosp在这里.

² http://climate.美国National航空航天局.gov/news/2915/the-atmosphere-getting-a-handle-on-carbon-dioxide/

³ 阅读更多关于生命周期阶段的信息 在这里.

⁴ ISO 21930第7节.2.9