What the three scopes mean
The Greenhouse Gas Protocol — the global standard for corporate and national emissions accounting, first published in 2001 — divides emissions into three categories based on where they originate relative to the entity being measured. The framework was designed for organisations, but the underlying logic applies equally to individuals. Understanding which scope an emission falls into determines who is responsible for reporting it and where action is most effective.
Scope 1 — direct emissions are produced by sources that an entity owns or directly controls. For a company, this means its furnaces, boilers, company-owned vehicles, and any on-site industrial processes. For an individual, Scope 1 emissions come from burning fuel at home — a gas boiler, an oil furnace, a propane stove — or from driving a petrol or diesel vehicle. The carbon dioxide and methane released during combustion happen directly, with no intermediary.
Scope 2 — indirect emissions from energy arise from electricity, steam, heat, or cooling that an entity purchases rather than produces itself. When you run a dishwasher or charge a laptop, the emissions occur at the power plant generating the electricity — not in your home. Those emissions are still attributed to you as the consumer of that energy. The US Environmental Protection Agency’s eGRID database (2023 release) puts the national average grid emission factor at 0.350 kg CO₂e per kilowatt-hour, though it varies substantially by region and energy mix.
Scope 3 — all other indirect emissions capture everything outside Scopes 1 and 2 — the full upstream and downstream value chain. For a company, this includes supplier emissions, employee commuting, business travel, the use and disposal of products sold, and financed activities. For individuals, Scope 3 is the largest category: the estimated emissions embedded in the food supply chain, manufactured goods, financial investments, and the infrastructure and services used daily. According to research published in the journal Science by Poore and Nemecek (2018), food system emissions alone — from land use through to retail — can range from under 1 ton CO₂e per year to over 4 tons CO₂e per year depending on diet, with beef and dairy the dominant drivers.
~70%
For most US households, Scope 3 emissions — goods, food, finance, and services — represent the majority of total estimated carbon footprint. Source: Exiobase 3.8.2 consumption-based accounting data.
Real examples by scope
Concrete examples make the framework easier to apply. The table below maps common individual activities to their scope category and provides indicative emission magnitudes based on published emission factors.
| Activity | Scope | Example magnitude | Source |
|---|---|---|---|
| Driving a petrol car | Scope 1 | ~0.21 kg CO₂e/km (avg US car) | EPA GHG Hub 2025 |
| Gas home heating | Scope 1 | ~2.0 tons CO₂e/yr (avg US home) | EPA GHG Hub 2025 |
| Home electricity use | Scope 2 | ~1.2 tons CO₂e/yr (avg US household) | EPA eGRID 2023 |
| Charging an EV | Scope 2 | 0.05–0.35 kg CO₂e/km (grid-dependent) | EPA eGRID 2023 |
| Transatlantic flight (economy) | Scope 3 | ~0.9–1.2 tons CO₂e per passenger | ICAO ICEC methodology |
| Diet (average omnivore, US) | Scope 3 | ~2.5 tons CO₂e/yr | Poore & Nemecek 2018 |
| Financed emissions (savings/investments) | Scope 3 | ~0.5–3.0 tons CO₂e/yr (portfolio-dependent) | PCAF Standard v3 |
Why Scope 3 is the hardest to measure — and the most important
The data problem
Scope 1 and Scope 2 emissions can usually be calculated from utility bills, fuel receipts, and meter readings — all of which carry documented emission factors. Scope 3 is harder because the data sits outside your direct control. The emissions embedded in a kilogram of beef depend on the farming method, feed supply chain, land use history, and transport distance — none of which appear on a supermarket receipt. Methodologies such as Exiobase 3.8.2 (a global multi-regional input-output database) and Poore and Nemecek’s 2018 lifecycle analysis of food systems provide the best available estimates for consumption-based footprinting, but they remain estimates with meaningful uncertainty ranges.
Why it cannot be ignored
Despite this uncertainty, Scope 3 cannot be ignored. For most individuals in high-income countries, it represents the majority of total estimated emissions. The IPCC Sixth Assessment Report (2022, Working Group III) highlights consumption-based accounting — which captures Scope 3 — as essential for understanding where mitigation opportunities are largest. Focusing only on Scopes 1 and 2 while ignoring diet, travel, goods, and finance would systematically undercount individual footprints by a large margin.
Note on double-counting
One reason the GHG Protocol separates scopes is to avoid double-counting when aggregating across organisations. A company’s Scope 3 business travel emissions are also an airline’s Scope 1 emissions. At the individual level this is less of a concern — personal carbon footprinting is consumer-side accounting, not producer-side — but it is worth understanding that Scope 3 estimates depend on supply-chain data that belongs to other entities.
How the scopes apply to personal carbon footprinting
Most personal carbon footprint calculators — including the Decarb calculator — cover all three scopes. The energy section captures Scopes 1 and 2. The transport, food, shopping, and finance sections are all Scope 3. A calculator that only covers home energy and personal vehicle use would miss the majority of most people’s estimated footprint.
For individuals, the most actionable insight from scope categorisation is that Scope 3 reductions — particularly in diet, flights, and financed emissions — tend to offer the largest absolute reduction potential. A shift from an average omnivore diet to a plant-rich one can reduce food-related estimated emissions by 1.0–1.5 tons CO₂e per year, according to Poore and Nemecek (2018). A single avoided long-haul flight can save more than an entire year of home electricity use in many US grid regions.
Where to focus your reduction effort
A scope-aware approach to reducing your personal footprint starts with identifying which category has the most room to move. For most people in the US, that means Scope 3. The steps below reflect the general priority order supported by published lifecycle and consumption-based accounting literature.
Estimate your full footprint across all three scopes. Without a baseline that covers Scopes 1, 2, and 3, it is impossible to identify where the largest reductions are available. A calculator that stops at energy and transport is incomplete.
Prioritise the highest-magnitude Scope 3 categories first. For most US households, flights, diet, and financed emissions (banking and investments) are the three largest Scope 3 line items. Addressing these before optimising, say, home appliance efficiency will typically deliver larger absolute reductions.
Then tackle Scopes 1 and 2 through electrification. Switching from gas heating to a heat pump and moving to an EV (or car-free transport) converts high-emission Scope 1 activities into Scope 2 — and Scope 2 emissions will decline as the electricity grid decarbonises, providing ongoing reductions without further individual action.
Address remaining emissions through high-quality removal. Once reduction options are exhausted or constrained by circumstance, verified carbon dioxide removal aligned with the Oxford Net Zero Principles (T2 and T3 removal methods) can address the residual footprint.
The Decarb methodology page documents the specific emission factors used to calculate Scope 1, 2, and 3 emissions across all categories: decarb.co/methodology. For a worked breakdown of how scope accounting applies to the average US footprint, see the post what is the average carbon footprint per American.
Frequently asked questions
What is the difference between Scope 1, 2, and 3 emissions?
Scope 1 emissions are direct — they come from sources you own or control, such as a gas boiler or petrol car. Scope 2 emissions are indirect and come from purchased electricity or heat: the emissions occur at the power plant, not at your home. Scope 3 covers all other indirect emissions across your full value chain, including the food you eat, the goods you buy, the flights you take, and the estimated emissions embedded in your financial holdings.
Does Scope 3 apply to individuals or just companies?
The GHG Protocol scope framework was originally designed for corporate emissions reporting, but the categories apply directly to individuals. For most people in high-income countries, Scope 3 — diet, flights, goods, and financed emissions — represents the largest portion of their total estimated carbon footprint. Personal carbon calculators that cover only energy and driving miss this majority share.
Why is Scope 3 so difficult to calculate accurately?
Scope 3 requires data from supply chains outside your direct control. The emissions embedded in food, manufactured goods, or investment portfolios depend on factors — land use, energy sources, logistics routes — that are not visible on a receipt or bank statement. Tools like Exiobase (a global input-output database) and the PCAF Standard for financed emissions provide the best available proxy estimates, but all Scope 3 figures carry more uncertainty than Scopes 1 and 2.
Which scope offers the biggest reduction opportunity for individuals?
For most individuals, Scope 3 offers the largest absolute reduction potential. A shift from an omnivore to a plant-rich diet can reduce estimated food-related emissions by 1.0–1.5 tons CO₂e per year, according to Poore and Nemecek (2018). Avoiding a single long-haul flight can save more estimated emissions than an entire year of average home electricity consumption in many US grid regions. Financed emissions — through bank and investment portfolio choices — are also material but harder to act on directly.
How does electrification affect scope categorisation?
Electrification converts Scope 1 emissions (direct combustion) into Scope 2 emissions (purchased electricity). Replacing a gas boiler with a heat pump or a petrol car with an EV moves those emissions from Scope 1 into Scope 2. This is strategically valuable because Scope 2 emissions fall automatically as the electricity grid decarbonises, delivering ongoing reductions without further individual action. In grid regions with high renewable penetration, this shift can be dramatic.
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Sources
- Greenhouse Gas Protocol. A Corporate Accounting and Reporting Standard. World Resources Institute / World Business Council for Sustainable Development, 2001 (revised 2015). ghgprotocol.org
- US EPA. Emissions & Generation Resource Integrated Database (eGRID) 2023. US Environmental Protection Agency, 2024. epa.gov/egrid
- US EPA. GHG Emission Factors Hub 2025. US Environmental Protection Agency, 2025.
- Poore, J. & Nemecek, T. “Reducing food’s environmental impacts through producers and consumers.” Science 360(6392), 987–992. 2018. DOI: 10.1126/science.aaq0216
- IPCC. Sixth Assessment Report, Working Group III: Mitigation of Climate Change. Intergovernmental Panel on Climate Change, 2022. ipcc.ch
- ICAO. ICAO Carbon Emissions Calculator (ICEC) Methodology. International Civil Aviation Organization, 2023.
- Stadler, K. et al. “Exiobase 3: Developing a Time Series of Detailed Environmentally Extended Multi-Regional Input-Output Tables.” Journal of Industrial Ecology 22(3), 502–515. 2018.
- Partnership for Carbon Accounting Financials (PCAF). The Global GHG Accounting and Reporting Standard for the Financial Industry, 2nd edition (v3). 2022. carbonaccountingfinancials.com
