When assessing greenhouse gas emissions in EIA, what emissions 'scope' is often the most challenging to quantify accurately?

When assessing greenhouse gas (GHG) emissions in EIA, Scope 3 emissions are often the most challenging to quantify accurately. GHG emissions are typically categorized into three scopes: Scope 1, Scope 2, and Scope 3. Scope 1 emissions are direct GHG emissions from sources that are owned or controlled by the reporting entity (e.g., emissions from burning fuel in on-site equipment). Scope 2 emissions are indirect GHG emissions from the generation of purchased electricity, heat, or steam consumed by the reporting entity. Scope 3 emissions encompass all other indirect GHG emissions that occur in the value chain of the reporting entity, both upstream and downstream. These can include emissions from the extraction and production of purchased materials, transportation of goods, employee commuting, and the use and disposal of products. Scope 3 emissions are often difficult to quantify because they involve a wide range of activities and sources that are outside the direct control of the reporting entity, requiring data collection and analysis from multiple sources across the value chain. For example, accurately estimating the emissions associated with the use of a product by consumers over its entire lifespan can be complex and uncertain.