For most Australian businesses, Scope 3 emissions represent the largest share of their carbon footprint… and the most difficult to measure, categorise and report. 

When Australian businesses begin their climate disclosure journey under AASB S2, they quickly discover that Scope 1 and Scope 2 emissions, while not trivial, are the manageable part. Scope 1 covers what you burn on site. Scope 2 covers the electricity you buy. The data is largely within your control and comes from your own operations. 

Scope 3 is a different story entirely. It captures everything else: the emissions generated across your entire value chain, from the suppliers who make your inputs to the customers who use and dispose of your products. For many organisations, Scope 3 can account for more than 70 per cent of total emissions. And yet it is the category that businesses are least prepared to report on. 

Scope 3 emissions are defined under the Greenhouse Gas Protocol and incorporated into Australia’s mandatory reporting framework through AASB S2. They are divided into 15 categories, split between upstream activities (what happens before a product or service reaches your business) and downstream activities (what happens after it leaves). 

Understanding which categories apply to your business is the essential first step. Not all 15 will be relevant, but identifying which ones are, and which are material enough to require disclosure, is itself a significant undertaking. 

The core challenge with Scope 3 is that most of the emissions sit outside your direct control and therefore, outside your direct line of sight. To report accurately, you need data from suppliers, logistics providers, customers and sometimes their suppliers in turn. That data is rarely sitting in one place, rarely in a consistent format and rarely collected with your reporting needs in mind. 

For upstream emissions, the difficulty lies in supplier engagement. Category 1 (Purchased goods and services) is typically the largest Scope 3 category for most businesses. Accurately measuring it requires emissions data from every significant supplier in your procurement chain. In practice, many suppliers, particularly smaller ones, do not yet measure or report their own emissions. You are often left relying on industry averages and emission factor databases, which introduce uncertainty into your figures. 

Downstream emissions bring a different set of challenges. You may have limited visibility into how your customers use your products, how they transport them or how they dispose of them at end of life. For a manufacturer selling into diverse markets, Category 11 (Use of sold products) can be enormous and genuinely difficult to estimate with precision. 

Scope 3 asks businesses to account for emissions they did not directly produce, using data they do not directly hold, from activities they do not directly control. 

Australian businesses in mining, agriculture and manufacturing face particular complexity here. Long and often international supply chains, diverse customer bases and limited supplier reporting maturity all compound the data challenge. There is no quick fix, but there are structured approaches that make the process manageable. 

Even once a business has gathered emissions data, a common stumbling block is working out which of the 15 categories it belongs in. The boundaries between categories are not always obvious, and misclassification can lead to double-counting or gaps in disclosure. 

Consider a mining company that contracts a third-party haulage provider to transport ore from the mine to port. Does that fall under Category 4 (Ppstream transportation and distribution) or is it better classified elsewhere? Or a financial institution with a large lending portfolio. Its most significant Scope 3 exposure likely sits in Category 15 (Investments) in the form of financed emissions, a category that requires an entirely different measurement methodology to most others. 

The GHG Protocol guidance and AASB S2 provide frameworks for making these determinations, but applying them to specific business activities requires judgment, sector knowledge and, in many cases, specialist advice. Getting the categorisation wrong does not just affect the accuracy of the numbers. It affects what gets disclosed, what gets managed and what regulators and investors can rely on

AASB S2 does not require businesses to report on every single Scope 3 category. What it requires is that all material categories are identified and disclosed. The question of materiality and which categories are significant enough to warrant reporting  is therefore central to the entire Scope 3 exercise. 

A category is generally considered material if it represents a significant share of total emissions, if it carries meaningful financial or reputational risk or if it is likely to be of interest to investors and lenders. For most businesses, a small number of categories will account for the vast majority of Scope 3 emissions. Category 1 (Purchased goods and services) and Category 11 (Use of sold products) are among the most commonly material, but this varies significantly by industry. 

The materiality assessment process should begin with a screening exercise (a high-level estimation of which categories are likely to be significant) before investing in the more detailed data collection and quantification work that material categories require. This sequencing saves time and resources and ensures effort is directed to where it matters most