How SAVE Works
SAVE tracks two of the highest-impact areas of everyday life: how you get around and what you eat. For each, the app calculates a CO₂ estimate and builds a personal picture of your habits over time — without ever sending your personal data to a server.
Transport
Every journey is logged on your device with its route, distance, duration, and travel mode — walk, bike, public transport, or car. CO₂ is calculated using standard emissions factors:
- Walking and cycling — zero direct emissions
- Public transport — approximately 0.05–0.08 kg CO₂ per km (shared vehicle average)
- Car — defaults to 0.21 kg CO₂ per km; you can update this in Settings to match your own vehicle
An on-device machine learning model analyses your travel patterns and suggests greener alternatives where they are realistic — for example, recommending the bike for a short commute you usually drive. All analysis runs locally on your phone. No trip data leaves your device.
Location Data
To calculate accurate distances and visualise your journeys, SAVE records the route of each trip on your device. This data is stored locally and never transmitted to any server. SAVE only captures location during an active trip — never continuously or in the background.
Meals
When you log a meal, SAVE identifies its main ingredients and estimates the climate impact of each one using global average emissions data. Rather than showing a precise CO₂ number — which would imply an accuracy we cannot guarantee — SAVE classifies each meal as Low, Moderate, or High impact.
This reflects the reality of food emissions data: the difference between a beef-heavy meal and a plant-based one is enormous and unambiguous, but the exact figure for any individual meal depends on origin, season, and preparation in ways we cannot know. The impact level captures what matters without overstating the precision.
The underlying CO₂ values come from the Poore & Nemecek (2018) study, the most comprehensive life-cycle analysis of food systems published to date, covering over 38,000 farms across 119 countries and published in Science.
Impact Levels
Every trip and meal is classified into one of three impact levels — Low, Moderate, or High — giving you an at-a-glance read of your choices without needing to interpret CO₂ numbers directly.
Transport
- Low — any walk, cycle, or public transport journey, plus short car trips under 1 kg CO₂
- Moderate — car trips producing 1–3 kg CO₂ (roughly a 5–15 km solo drive)
- High — car trips producing more than 3 kg CO₂
Food
Meal thresholds are informed by the WWF One Planet Plate guide (~1.5 kg CO₂e per meal) and the distribution of our own meal database:
- Low — under 1.5 kg CO₂e (plant-forward meals, fish, poultry)
- Moderate — 1.5–4 kg CO₂e (mixed meals with some animal protein)
- High — above 4 kg CO₂e (beef- or lamb-heavy meals)
Personal Progress Score
Rather than comparing you to a global average, SAVE measures you against yourself. Your score reflects how your current behaviour compares to your own personal baseline — the habits you had when you first started using the app.
This means progress is always meaningful and achievable, regardless of where you are starting from. A small improvement in a high-impact habit counts for more than a large improvement in a low-impact one.
What We Do Not Claim
- We do not store your trips, meals, location coordinates, or personal behaviour on any server
- We do not track your location continuously or in the background — only during an active trip
- We do not build profiles or sell data to third parties
- We do not use global averages to judge your habits — only your own history
- Our estimates are scientifically grounded approximations intended to guide decisions, not audit them. Food and transport emissions vary by region, season, and supply chain
Data Sources
SAVE's CO₂ figures are derived from peer-reviewed research and open datasets.
Food Emissions — Poore & Nemecek (2018)
All food CO₂ values are sourced from:
Poore, J. & Nemecek, T. (2018). "Reducing food's environmental impacts through producers
and consumers." Science, 360(6392), 987–992. doi:10.1126/science.aaq0216
Accessed via Our World in Data. Licensed under CC BY 4.0.
Meal Recipes — TheMealDB
Meal ingredient breakdowns are sourced from TheMealDB, an open community recipe database. Licensed under CC BY-SA 4.0.
A Note on Accuracy
Food and transport emissions are inherently variable. A tomato grown in a heated greenhouse has a very different footprint from one grown outdoors in season. A car driven at motorway speed emits differently from one idling in traffic. Our figures represent well-established averages from the best available research — accurate enough to make meaningful comparisons and guide better choices, which is exactly what SAVE is designed to help you do.