The greenhouse gas emissions associated with bioenergy are often temporally dispersed and can be a mixture of long-term forcers (such as carbon dioxide) and short-term forcers (such as methane). These factors affect the timing and magnitude of climate-change impacts associated with bioenergy in ways that cannot be clearly communicated with a single metric. This is critical as key comparisons that determine incentives and policy for bioenergy are based upon climate-change impacts expressed as carbon dioxide equivalent calculated with GWP100. This paper explores these issues further and presents a spreadsheet tool to facilitate quick assessment of these temporal effects. The potential effect of (i) a mix of GHGs and (ii) emissions that change with time are illustrated through two case studies. In case study 1, variations in the mix of greenhouse gases mean that apparently similar impacts after 100-years, mask radically different impacts before then. In case study 2, variations in the timing of emissions cause their climate-change impacts (integrated radiative-forcing and temperature change) to differ from the impacts that an emissions-balance would suggest. The effect of taking alternative approaches to considering “CO₂-equivalence” are also assessed. In both cases, a single metric for climate-change effects was found to be wanting. A simple tool has been produced to help practitioners evaluate whether this is the case for any given system. If complex dynamics are apparent, it is recommended that additional metrics, more detailed inventory, or full time-series impact results are used in order to accurately communicate these climate-change effects.

与生物能源相关的温室气体排放通常在时间上是分散的，并且可以是长期压力源（例如二氧化碳）和短期压力源（例如甲烷）的混合物。这些因素以无法用单一指标清晰传达的方式影响与生物能源相关的气候变化影响的时间和程度。这是至关重要的，因为确定生物能源奖励措施和政策的关键比较是基于气候变化影响，以GWP100计算的二氧化碳当量表示。本文将进一步探讨这些问题，并提出一种电子表格工具，以帮助快速评估这些时间效应。通过两个案例研究说明了（i）温室气体混合和（ii）随时间变化的潜在影响。在案例研究1中，温室气体混合的变化意味着100年后的影响显然相似，但此后掩盖了根本不同的影响。在案例研究2中，排放时间的变化导致其气候变化影响（综合辐射强迫和温度变化）与排放平衡所暗示的影响不同。采取替代方法考虑“ CO”的影响还评估了“ _2-等价性”。在这两种情况下，都需要一个衡量气候变化影响的指标。已经产生了一个简单的工具来帮助从业者评估任何给定系统是否属于这种情况。如果复杂的动态显而易见，建议使用其他指标，更详细的清单或完整的时间序列影响结果，以准确传达这些气候变化影响。