"Our model emphasises clarity over complexity — using accessible inputs and internally validated factors. Wherever possible, we prioritise consistency, avoid false precision, and align with Decarb's mission to make carbon reduction measurable and continuous."
01 — Flights
Flight emissions are calculated using ICAO-based fixed factors per flight type. Decarb uses flight duration as the input — simpler for users than distance-based entry. For detailed single-flight calculations, we recommend the ICAO Carbon Emissions Calculator.
| Flight type | Reference route | Duration | Estimated emissions (tons CO₂e) |
|---|---|---|---|
| Short-haul | NYC → Chicago | 2h 33m | 0.296 |
| Medium-haul | NYC → Los Angeles | 5h 18m | 0.608 |
| Long-haul | NYC → Rome | 8h 08m | 0.775 |
Source: ICAO Carbon Emissions Calculator. Values per one-way flight.
Only CO₂ is included in v2.2. Aviation's non-CO₂ climate effects — contrails, NOx, induced cloudiness — can roughly double the climate impact of a flight (Radiative Forcing Index of 1.9–2.7). These are excluded in this version to maintain comparability with EPA and ICAO baselines and avoid user confusion. Inclusion of non-CO₂ effects is under consideration for future updates.
02 — Home energy
Emissions are calculated from housing type combined with energy source. Scope covers operational emissions only (Scope 1 and 2). Based on US EIA average electricity use of 10,500 kWh/year, eGRID intensity of 0.42 kg CO₂/kWh, and EPA gas factor of 5.3 kg CO₂/therm.
| Housing type | Renewable only (tons CO₂e) | Electricity only (tons CO₂e) | Electricity + gas (tons CO₂e) |
|---|---|---|---|
| Shared flat | 0 | 0.6 | 1.1 |
| Flat / condo | 0 | 1.0 | 1.6 |
| Semi-detached home | 0 | 1.3 | 2.0 |
| Detached home | 0 | 1.7 | 2.5 |
Sources: US EIA, eGRID, EPA. Values in tons CO₂e per person per year.
Emission factors vary by housing type due to differences in average size, energy intensity, and occupancy. Shared flats have lower per capita emissions due to smaller living space and shared walls. Detached homes average around 2,500 ft² with higher HVAC loads; apartments average 1,000–1,200 ft². Occupancy is assumed at 2.5 persons per household.
Fuel oil and propane are excluded from this version. Upstream methane leakage is not included in operational totals.
03 — Food
Food emissions are estimated from dietary pattern using lifecycle emission factors from US-based sources. Scope covers farm to retail. Cooking and food waste are modelled separately.
| Diet type | Used value (tons CO₂e) | Reference range (tons CO₂e) | Main source |
|---|---|---|---|
| Vegan | 0.4 | 0.3 – 0.5 | Poore & Nemecek; GreenFi |
| Vegetarian | 1.2 | 1.0 – 1.4 | Heller & Keoleian (US LCA) |
| Flexitarian (limited meat and dairy) | 1.7 | 1.5 – 2.0 | USDA dietary modelling |
| Omnivore (daily meat and dairy) | 2.3 | 2.0 – 2.5 | USDA, CoolClimate |
No regional dietary variance applied. Results are indicative averages.
04 — Waste
Net waste footprint = emissions from landfilled waste minus avoided emissions from recycling and composting. Based on US EPA WARM Model with average waste generation of approximately 0.8 tons per person per year.
| Waste behaviour | Estimated emissions (tons CO₂e/year) |
|---|---|
| I do not recycle | 0.42 |
| I recycle | 0.27 |
| Minimalist (reduce, reuse, recycle) | 0.15 |
Source: US EPA WARM Model. Mixed MSW landfill factor ~0.59 tons CO₂e/ton. Credits applied for diverted materials. Composting included in minimalist scenario.
05 — Goods and services
Emissions are estimated from monthly spending bracket multiplied by an emission-weighted basket of categories using EEIO-based factors. Calibrated to US Consumer Expenditure Survey averages.
| Monthly spending bracket | Annual spend (USD) | Estimated emissions (tons CO₂e) |
|---|---|---|
| Less than $150 | $1,200 | 0.65 |
| $150 – $300 | $2,700 | 1.45 |
| $300 – $500 | $4,800 | 2.55 |
| More than $500 | $6,600+ | 3.60 |
Category weights
| Category | Share of spend | Emission factor (tons CO₂e per $) |
|---|---|---|
| Clothing and footwear | 10% | 0.20 |
| Furniture and appliances | 15% | 0.42 |
| Entertainment and recreation | 10% | 0.17 |
| Other goods | 25% | 0.33 |
| Services (health, etc.) | 40% | 0.19 |
Sources: GreenFi modelling, Exiobase EEIO factors, US Consumer Expenditure Survey. Electronics counted once at point of purchase to avoid overestimation.
06 — Finance
Finance emissions reflect how personal savings and investments are used by banks and funds — known as financed emissions. These are indirect (Scope 3) and can show high values. The assumptions below are based on typical US account sizes: $20,000 held in a traditional bank and $100,000 in investments. These assumptions are stated explicitly to maintain transparency.
| Financial behaviour | Estimated emissions (tons CO₂e/year) | Basis |
|---|---|---|
| Standard banking and investment | 6.0 | $20k in bank (0.24 kg CO₂e/$-yr) + $100k invested (0.033 kg CO₂e/$-yr) |
| No investments or bank account | 0 | No formal financial footprint modelled |
| Green investing and fossil-free banking only | 2.0 | $20k in green bank (0.057 kg/$) + $100k in green fund (0.017 kg/$) |
Sources: GreenFi, PCAF (Alexander et al. 2023), Project Drawdown, GHG Protocol Category 15, Federal Reserve data.
Finance emissions are not due to personal spending behaviour but to how banks and funds allocate capital. This category often produces the largest single contribution to an individual footprint. Switching to green banking and investment alternatives can produce large reductions — this reflects the underlying data, not an exaggerated claim.
07 — Other activities
Emissions are assigned only for explicitly carbon-intensive hobbies. Social and leisure activities already captured under food or goods categories are not double-counted here.
| Lifestyle description | Estimated emissions (tons CO₂e/year) | Notes |
|---|---|---|
| Outdoor physical activities only (hiking, running, yoga) | 0 | No direct emissions |
| Occasional bars, restaurants, cinema | 0 | Captured under food and goods categories — not double-counted |
| Frequent bars, restaurants, cinema | 0 | Same as above |
| Carbon-intensive hobbies (motorboating, motorsports) | 0.6 | Estimated from ~50 hours/year of high-emission leisure activity |
Only direct fuel-burning leisure activities are assigned emissions. All other categories are covered elsewhere to avoid overlap.
08 — Ground transport
Emissions are calculated from vehicle type multiplied by a fixed emission factor based on US averages. Scope covers operational vehicle emissions (Scope 1). EV electricity emissions use national grid average (Scope 2). Assumes 12,000 miles per year — US average per FHWA data.
| Transport mode | Estimated emissions (tons CO₂e/year) | Basis |
|---|---|---|
| No personal vehicle / public transit | 0.45 | Bus, train, and occasional rideshare |
| Hybrid or efficient car | 1.8 | 12,000 mi/yr at 45 MPG |
| Standard petrol car | 3.1 | 12,000 mi/yr at 25 MPG (US average) |
| Large SUV or truck | 4.5 | 12,000 mi/yr at 17 MPG |
| Electric vehicle | 0.9 | 12,000 mi/yr, 0.34 kWh/mile, grid intensity 0.42 kg CO₂/kWh |
Sources: US EPA Emissions Factors Hub, FHWA vehicle miles travelled data, eGRID. Tailpipe emissions only for ICE vehicles. Vehicle manufacturing and embodied emissions excluded for consistency.
References
- US EPA Emissions Factors Hub (2024)
- ICAO Carbon Emissions Calculator
- GHG Protocol Scope 3 Technical Guidance
- GreenFi Carbon Footprint Methodology
- CoolClimate UC Berkeley
- Poore, J. & Nemecek, T. (2018). Reducing food's environmental impacts through producers and consumers. Science, 360(6392), 987–992.
- Heller, M.C. & Keoleian, G.A. (2015). Greenhouse Gas Emission Estimates of US Dietary Choices and Food Loss. Journal of Industrial Ecology.
- PCAF — Partnership for Carbon Accounting Financials. Global GHG Accounting and Reporting Standard.
Questions and corrections
If you identify an error in our methodology or emission factors, contact us at [email protected]. We take accuracy seriously and will investigate and correct any verified errors promptly.