Part 1: From data to disclosure: GHG inventory basics for business

Executive summary 

Regulators, investors, customers, and insurers now expect decision‑grade emissions data. A robust greenhouse gas (GHG) inventory is a core business capability that enables compliance, lowers operating costs, and protects access to capital. 

Why it matters: Inventories underpin regulatory readiness, improve financing and insurance terms, and reveal margin opportunities in energy, fleet, and supply chains. 

What’s inside: Clear guidance on scopes 1, 2, and 3, organizational boundaries, calculation methods, data sources, and emission factor selection. 

How to start: Define boundaries, prioritize energy and fuel data, apply a repeatable methodology, and build documentation and governance alongside calculations. 

What “good” looks like: Audit‑ready disclosures, both location‑ and market‑based scope 2 reporting, prioritized scope 3 categories, strong controls, and a recalculation policy for structural changes. 

Introduction 

As climate disclosure expectations grow and sustainability goals become more ambitious, many organizations are asking the same question: where do we begin?  

For every organization, the answer begins with compiling a greenhouse gas (GHG) inventory. Just as financial accounting provides an annual, auditable view of a company’s financial performance, carbon accounting delivers a consistent picture of an organization’s emissions footprint year over year. 

In 2026, many business leaders no longer regard their greenhouse gas inventory as a sustainability add-on, but as a core business capability. Regulatory developments such as California’s Climate Corporate Data Accountability Act (SB 253), alongside global disclosure frameworks like CSRD and ISSB, are raising expectations for accurate, decision-ready emissions data — even as requirements continue to evolve.  

At the same time, investors, customers, insurers, and lenders increasingly expect robust emissions data.  

Done well, a GHG inventory underpins risk management, cost control, and regulatory readiness. It strengthens access to capital and insurance, supports credible disclosures, and protects margins by surfacing energy, fleet, and supply‑chain efficiency opportunities that might otherwise remain hidden. 

What is a GHG inventory and why does it matter?  

A GHG inventory is an accounting of all the greenhouse gas emissions associated with an organization’s activities over a defined period, typically one year. Emissions are quantified in carbon dioxide equivalents (CO₂e) enabling different greenhouse gases to be measured and compared on a consistent basis. A well-constructed GHG inventory serves as the foundation for:  

• Corporate climate targets and decarbonization strategies  
• Risk management and climate-related scenario planning  
• Regulatory and voluntary disclosures  
• Investor, lender, and insurer confidence  

Most importantly, a GHG inventory establishes a credible baseline. Without it, targets lack context, progress cannot be measured reliably, and disclosures are difficult to defend. With a strong baseline in place, organizations can move beyond reporting to informed decision-making: strategy development, target setting, prioritizing actions, allocating capital, and tracking performance over time.  

In this way, a GHG inventory is not simply a compliance exercise. It is a management tool that connects sustainability objectives with operational and financial outcomes. 

The GHG Protocol: the guiding framework  

The GHG Protocol is the globally accepted standard for corporate GHG accounting. Developed by the World Resources Institute (WRI) and the World Business Council for Sustainable Development (WBCSD), it provides clean guidance on what to measure, how to calculate emissions, and how to maintain consistency and transparency over time. The GHG Protocol is built around five core principles:  

• Relevance: Include emission sources that materially affect business decisions and stakeholder understanding 
• Completeness: Cover all significant emissions within the defined boundary and reporting period 
• Consistency: Apply stable methodologies and boundaries over time; disclose and justify any changes 
• Transparency: Document data sources, assumptions, calculation methods, and uncertainties in a clear and traceable way 
• Accuracy: Use high-quality data and appropriate emission factors to minimize error and bias 

GHG emissions are categorized into three scopes under the GHG Protocol based on where they occur and how directly they are controlled:  

• Scope 1: Direct emissions from sources owned or controlled by the company, such as onsite fuel combustion, or fuel for company vehicles. 
• Scope 2: Indirect emissions from purchased electricity, steam, heating, and cooling consumed by the organization. 
• Scope 3: Indirect emissions that occur across the value chain, both upstream and downstream from your operations, including transportation and distribution, employee commuting and business travel, purchased goods and services, and the use of sold products.  

For organizations beginning their GHG accounting journey, scope 1 and 2 emissions are the logical starting point. Luckily, these operational emissions are generally more straightforward to account for, as they rely on data many companies already track, such as utility bills, fuel invoices, metered energy consumption, and fleet records. 

In fact, for many organizations, this is data that Trio already manages or has access to through energy procurement, bill validation, and fleet-related services. Leveraging existing energy data not only accelerates inventory development but also improves accuracy and audit readiness by building calculations using primary sources.  

Scope 3 emissions, by contrast, tend to be more complex to estimate due to limited direct data: for most organizations, scope 3 makes up the bulk of their GHG footprint, often representing 90% or more of total emissions. When first starting out with scope 3, it is okay to start small. Focus on a few key scope 3 categories such as purchased goods and services, business travel, and employee commuting, which can be estimated using spend data. As your data collection and management processes become more refined over time, your calculations will become more precise. Scope 3 GHG accounting is a journey: instead of chasing perfection, focus on making small improvements year over year.  

Setting boundaries, crunching the numbers 

Before calculations begin, companies must define their organizational boundary, which defines which operations, subsidiaries, and locations should be included in the inventory. The GHG Protocol allows organizations to define their boundary under a few different approaches, but most firms opt for an operational control approach, under which a company accounts for 100% of emissions from its own operations, or operations over which it has full authority to introduce and implement operating policies. 

Then it’s time for the emissions calculation methodology. At its core, GHG accounting follows a straightforward formula:  

• Activity Data × Emission Factor = Emissions  

The challenge here lies not in the math, but in the quality, completeness, and traceability of the inputs.  

A strong inventory starts with strong data. Activity data are quantitative measures of actions that cause GHG emissions: think kWh of electricity consumed, gallons of diesel used, or kg of waste generated.  

Where do these come from? Common activity data inputs include:  

• Utility bills (electricity, natural gas)  
• Fuel purchase records and invoices  
• Metered energy data  
• Fleet and equipment fuel use  
• Operational and production data  

Remember: a company’s GHG inventory is only as good as its data, and where possible, primary data is always preferable. While it is likely that you will need to develop assumptions where there are challenges to data availability, incomplete, inconsistent, or poorly documented data can undermine your inventory. This requires developing, documenting, and implementing consistent methodologies for missing data or for gap-filling.  

But don’t be discouraged: your data gathering processes will improve over time.    

Emission factors 

Getting reliable emissions figures involves using emission factors, which convert activity data (such as kWh of electricity or therms of natural gas) into a carbon dioxide-equivalent (CO₂e) value. These values vary by emission source, location, year, and other considerations. Many governments publish emission factor datasets for this purpose: see, for example, the U.S. EPA GHG Emission Factors Hub, or the U.K. DEFRA GHG Conversion Factors.   

Applying the right emission factor and documenting its source is essential for accuracy and credibility. This is where expertise matters, because identifying the appropriate factors isn’t always straightforward. Here, the GHG Protocol Corporate Standard is a lifeline for understanding calculation methodologies and best practices based on your best available data.  

How to get started 

To recap, kicking off your GHG inventory doesn’t require perfection, but it does require structure, good data, and the right expertise. Practical first steps include:  

• Defining organizational boundaries  
• Prioritizing energy and fuel data collection  
• Establishing a repeatable methodology based on best practice  
• Developing documentation and governance alongside calculations  

Whether you’re building your first GHG inventory or strengthening an existing one, the path from data to disclosure starts with the fundamentals, and the right partner. Trio helps companies bridge the gap between raw energy data and meaningful climate disclosures. Trio’s deep energy expertise ensures inventories are not only accurate but actionable, supporting smarter decisions, stronger strategies, and credible progress.  

Next steps: 

• Join our GHG Inventory Office Hours for a discussion on boundary setting, methodology, controls, and what “assurance-ready” looks like in practice. 
• Alternatively, share a few details or questions about your GHG inventory, and our team will follow up to provide initial guidance. 

Partner with Trio today to start converting emissions data into margin, resilience, and growth.