Our approach
Arenius follows the approach used by leading carbon accountants: apply the most accurate method available for each transaction, and be transparent about which method was used. In practice that means a simple rule: use real physical activity data wherever your records provide it, and fall back to spend-based estimates only where they don't.
Activity-based
When a record shows a real physical quantity, such as litres, kWh, kilometres, or kilograms, we apply the official unit-based emission factor for that activity.
Ministry for the EnvironmentSpend-based
When a transaction is just a dollar amount with no quantity attached, we estimate the emissions embodied in each dollar spent on that type of good or service.
Stats NZ input-output modelActivity data first
Wherever your records show a real physical quantity, we use it. Litres of fuel, kilowatt-hours of electricity, kilometres travelled, kilograms of waste to landfill: for these we apply the official emission factors published by the Ministry for the Environment (MfE) in its annual Measuring Emissions guide.
These unit-based factors are the gold standard. They reflect the actual physical activity behind a transaction rather than estimating from its dollar value, which makes them far more accurate. MfE refreshes them every year, and so do we.
| Activity | Physical unit | Factor source |
|---|---|---|
| Fuel combustion | Litres | MfE Measuring Emissions |
| Electricity | Kilowatt-hours (kWh) | MfE Measuring Emissions |
| Travel & freight | Kilometres | MfE Measuring Emissions |
| Waste to landfill | Kilograms | MfE Measuring Emissions |
Spend-based factors fill the gaps
Most business spending doesn't arrive with a quantity attached. You have a $180 invoice for office supplies, not a weight in kilograms. For transactions like these, Arenius uses spend-based emission factors: the estimated emissions embodied in each dollar spent on a given type of good or service.
An $180 invoice for office supplies has no litres or kilograms to measure, so Arenius applies the spend-based factor for that category to the dollar value, estimating the emissions embodied in the purchase.
Our spend-based factors are grounded in New Zealand data. They are derived from an environmentally-extended input-output model built on Statistics New Zealand's Supply-Use Tables and national greenhouse gas emissions accounts. This traces emissions all the way up each product's supply chain, so the factor for a loaf of bread already accounts for the baking, the flour milling, the wheat farming, and the transport in between.
A single spend-based factor already rolls up every emission along the chain, so one line in your accounts captures the full embodied footprint.
We then tune these factors so they fit real transactions:
Matched to what you actually pay
Factors are expressed at purchaser's prices, so they apply directly to your transaction values.
Kept current
Factors are inflation-adjusted to present-day dollars using the Consumers Price Index, correcting for the lag inherent in national economic data.
Honest by design
Spend-based figures are estimates, and we show them as estimates. As your data improves, a power bill here, a fuel record there, Arenius upgrades those lines from spend-based estimates to activity-based measurements, and your footprint sharpens over time.
Nothing is hidden behind a single number. Every line carries its method, so you always know how much of your footprint is measured versus estimated, and it only gets sharper as you connect more data.
Standards & data sources
Our methodology is aligned with the GHG Protocol, the world's most widely used greenhouse gas accounting standard, and built entirely on recognised New Zealand government data sources.