Methodology & transparency
A default is
never silent.
Understand the GreenTurtle Standard v1 methodology. Every carbon figure needs a source, a period, a unit and a method.
Scope: know the limits
Annual CO₂e is estimated for unarchived vehicles using distance × an emissions factor. This is not measured fuel or electricity use. Grey fleet, well-to-tank emissions and vehicle embodied carbon are outside v1. The figures support management, engagement and directional reporting; they do not provide disclosure assurance.
Distance: show the source
Use recorded contracted annual mileage first. If it is unavailable, use lifetime odometer divided by vehicle age. If neither is available, use a clearly labelled default of 8,000 miles per year. An odometer-derived annual distance is an estimate, not a measured annual total. Defaults must be visible and included in a defaults-in-use count.
Powertrain: use the right treatment
Battery electric vehicles use a DESNZ average BEV per-kilometre factor, counting grid electricity. Plug-in hybrids use a DESNZ average PHEV per-kilometre factor rather than their WLTP figure. Petrol, diesel and non-plug-in hybrids with a recorded type-approval figure use WLTP gCO₂/km × 1.15. Where no g/km figure is recorded, use the named DESNZ average for the fuel and body type (car or van).
Factors: keep the version visible
The supplied v1 method, published 4 Sep 2026, specifies DESNZ 2026 conversion factors and explicit powertrain rules. It states that values were seeded from a secondary aggregation on 4 Sep 2026 and remain unchecked until each is compared with the official spreadsheet. An assessment should state the factor source, method version and period. This marketing site does not run the carbon calculation or claim that a live factor table has been independently checked.
Progress: build a real baseline
A year-on-year change is shown only when a snapshot around 12 months old exists to calculate it from. Until then, the status is “Baseline is building”. Explain changes in fleet size, vehicle mix, coverage or assumptions when interpreting a comparison.
Claims: say what the evidence supports
The GreenTurtle Standard is self-assessed. It does not provide an audit, third-party certification or assurance against GHG Protocol, ISO 14083 or SECR. A battery-electric vehicle is zero-tailpipe, not zero-carbon. A tier does not establish carbon neutrality.
Records: connect the mark to the summary
A displayed Standard mark must include its verification code or link. The public record should state the self-assessed status, reporting period, method and whether the record has been revoked. A code identifies a record; it is not an independent assurance opinion.
Default distance
8,000 miles/year · no contracted mileage or usable odometer-derived estimate · GreenTurtle Standard v1. This is a method example, not a fleet result or emissions total.
Read the original method
The supplied source document is available below. This page is a plain-English summary; it does not reproduce an operational calculation engine.
Download the supplied Standard v1 method (Markdown)Source: GreenTurtle Standard v1, published 4 Sep 2026, and the supplied GreenTurtles design-system README.