What we count and how
Our carbon footprint is given in kg CO2e per person: kilograms of carbon-dioxide equivalent, the standard unit that combines all greenhouse gases into one comparable figure. Every figure is an activity multiplied by an emission factor.
Emissions (kg CO2e) = activity data × emission factor of that activity
The footprint of a retreat or journey has four parts: travel to the destination, travel in the destination, accommodation and meals. The method follows the Greenhouse Gas Protocol principle of activity data multiplied by an emission factor, uses indirect (Scope 3) factors for the services a traveler buys, and was inspired by the VisitScotland Holiday Carbon Calculator. We added two things to that model: the number of people sharing a room, and the number of travelers sharing a vehicle, because emissions are measured per room and per vehicle, not per person.
We calculate each carbon report after the retreat or journey, from the final number of participants. Where a supplier publishes no emission data, we use the published reference factors listed below and say so. Nothing is invented: every factor has a source in the list at the bottom of this page.
Travel to the destination
Getting to the start of a retreat is usually the largest share of a footprint. Each traveler enters their own journey, so it is not part of the retreat figure in our reports.
Source: UK Government GHG Conversion Factors for Company Reporting 2024 (Excel file "Conversion factors 2024: full set"), worksheets for business travel by air, sea and land, each with its well-to-tank (WTT) worksheet. We use the total of the direct emissions and the WTT emissions, which cover extracting, refining and transporting the fuel. For flights we use the international "average passenger" factor including the radiative forcing effect, which accounts for the extra warming of emissions released at altitude.
| Transport | Direct | WTT | Total kg CO2e |
|---|---|---|---|
| Plane (international, per passenger-km) | 0.1758 | 0.02162 | 0.19742 |
| Car, petrol (per km) | 0.1645 | 0.04599 | 0.21049 |
| Car, diesel (per km) | 0.16984 | 0.04146 | 0.2113 |
| Car, LPG (per km) | 0.19718 | 0.02341 | 0.22059 |
| Car, electric (per km) | 0.04745 | 0.01049 | 0.05794 |
| Car, hybrid (per km) | 0.12607 | 0.03315 | 0.15922 |
| Train (international rail, per passenger-km) | 0.00446 | 0.00117 | 0.00563 |
| Bus (coach, per passenger-km) | 0.02717 | 0.00656 | 0.03373 |
| Campervan, petrol (per km) | 0.22095 | 0.06183 | 0.28278 |
| Campervan, diesel (per km) | 0.25023 | 0.06128 | 0.31151 |
| Ferry (average passenger, per passenger-km) | 0.1127 | 0.02555 | 0.13825 |
To let travelers enter a journey as hours of travel, we convert each factor with a realistic average speed that includes stops and traffic: plane 550 km/h on short routes and 850 km/h on long routes, car 80 km/h, train 100 km/h, bus 70 km/h, campervan 70 km/h and ferry 38 km/h.
| Transport | Calculation | kg CO2e per hour |
|---|---|---|
| Plane | 550 km/h × 0.19742 = 108.6, used as 110 | 110 |
| Car, petrol | 80 km/h × 0.21049 | 16.8 |
| Car, diesel | 80 km/h × 0.2113 | 16.9 |
| Car, LPG | 80 km/h × 0.22059 | 17.6 |
| Car, electric | 80 km/h × 0.05794 | 4.6 |
| Car, hybrid | 80 km/h × 0.15922 | 12.7 |
| Train | 100 km/h × 0.00563 | 0.6 |
| Bus | 70 km/h × 0.03373 | 2.4 |
| Campervan, petrol | 70 km/h × 0.28278 | 19.8 |
| Campervan, diesel | 70 km/h × 0.31151 | 21.8 |
| Ferry | 38 km/h × 0.13825 | 5.3 |
Cars and campervans are counted per vehicle, so the hourly figure is divided by the number of people in the vehicle.
Example, a direct flight New York to Dubrovnik: 7,260 km × 0.19742 kg CO2e per passenger-km = 1,433.27 kg CO2e per passenger.
As a cross-check, the flight calculator of the Swiss climate organisation myclimate gives about 1.4 t CO2e per passenger for the same route in economy class. Flight calculators differ by the radiative forcing effect, aircraft type, load factor, travel class and whether fuel production is included.
Travel in the destination
Land transport
We count the emissions of the vehicle for the distance driven during the retreat or journey and share them between the travelers on board. Our groups are small: we use a mid-size car for up to 4 people and a van for 5 to 8 people. Groups of 9 to 11 use one car and one van, and groups of 12 to 16 use two vans. Most vehicles are rented, so we use the business-travel-by-land worksheets with WTT emissions.
| Vehicle | Direct | WTT | Total kg CO2e per km |
|---|---|---|---|
| Mid-size car, diesel (used) | 0.16807 | 0.04103 | 0.2091 |
| Van, diesel (used) | 0.20729 | 0.0507 | 0.25799 |
| Mid-size car, petrol | 0.17726 | 0.04957 | 0.22683 |
| Van, petrol | 0.26885 | 0.07528 | 0.34413 |
| Mid-size car, LPG | 0.17634 | 0.02093 | 0.19727 |
| Van, LPG | 0.26759 | 0.03179 | 0.29938 |
| Mid-size car, hybrid | 0.1149 | 0.02998 | 0.14488 |
| Van, hybrid | 0.15486 | 0.03961 | 0.19447 |
| Group size | Vehicle(s) | kg CO2e per vehicle-km |
|---|---|---|
| 1 to 4 | 1 car | 0.2091 |
| 5 to 8 | 1 van | 0.25799 |
| 9 to 11 | 1 car + 1 van | 0.46709 |
| 12 to 16 | 2 vans | 0.51598 |
Emissions per person (kg CO2e) = distance (km) × emission factor (kg CO2e per km) ÷ number of travelers
Example: 700 km in a diesel van with 6 travelers = 700 × 0.25799 ÷ 6 = 30.10 kg CO2e per person.
Ferries
We have not received emission data from the ferry operators on our routes, so we use the sea-travel worksheets of the same UK Government factors, with WTT emissions. A passenger on foot and a driver with a vehicle are counted separately and the results are added up.
| Ferry | Direct | WTT | Total kg CO2e per km |
|---|---|---|---|
| Per passenger | 0.01871 | 0.00424 | 0.02295 |
| Per passenger with a vehicle | 0.12933 | 0.02932 | 0.15865 |
Private boats and sailing
For a private speedboat transfer we use a 200 hp outboard engine: fuel consumption of about 90 litres per hour at an average speed of 58 km/h (boat-fuel-economy.com), which is 1.5517 litres per km. With the petrol factor of 2.0844 kg CO2e per litre from the UK Government factors, this gives 3.234 kg CO2e per km for the whole boat, divided by the people on board.
For sailing with occasional use of the motor we use the operating data of our catamaran partner: 18 litres of diesel for a 111 km route. With the diesel factor of 2.51279 kg CO2e per litre, this gives 0.407 kg CO2e per km for the whole boat, divided by the people on board.
Accommodation
Very few accommodations in Croatia measure their emissions, and no national or UK Government dataset covers accommodation in Croatia. We use the average emissions of hotels in Croatia from the Hotel Footprinting Tool developed by the International Tourism Partnership and Greenview. It is based on the Cornell Hotel Sustainability Benchmarking Index, which uses annual data from international hotel companies and the industry standard of the Hotel Carbon Measurement Initiative (HCMI). It covers the hotel's own operations: energy, water and refrigerants (Scope 1 and 2).
| Accommodation | kg CO2e per room per night |
|---|---|
| 2-star hotel (also used for private accommodation) | 6.0 |
| 3-star hotel | 9.7 |
| 4-star hotel | 11.9 |
| 5-star hotel | 19.6 |
Emissions are measured per room, not per person. A room shared by two people halves each person's share, and a single room carries the whole figure.
Emissions per person (kg CO2e) = number of nights × kg CO2e per room per night ÷ people in the room
When a retreat is calculated before the final rooming is known, we assume about 70% double rooms and 30% single rooms of a venue's participant rooms. For a hotel-based retreat we assume a standard group of 10 participants: 4 double and 2 single rooms. We use the real room types of the group when we know them. In future we plan to ask partner accommodations to calculate their own emissions with the HCMI standard and use those figures instead.
Meals
Meals have three components: the emissions of producing the food, the emissions of food waste, and the emissions of preparing the meal. Food emissions come from the life cycle of the food, from production to the shop, based on Our World in Data and the study by Poore and Nemecek (2018) in Science. That study includes land-use change, farm emissions, animal feed, processing, transport to retail and packaging.
For food waste we assume that 10% of each solid meal is wasted, and use 1.93 kg CO2e per kg of food waste. That figure comes from the European Parliament: 88 million tonnes of food are wasted in the EU each year, causing 170 million tonnes of CO2e (European Parliament). Preparing a meal adds about 0.1 kg CO2e per person, a very small share, so we leave it out.
| Meal | Vegan | Vegetarian | Mixed |
|---|---|---|---|
| Breakfast, kg CO2e per person | 0.40304 | 1.625 | 3.8447 |
| Lunch or dinner, kg CO2e per person | 0.651 | 3.297 | 4.01299 |
The mixed lunch or dinner figure is the average of all lunch and dinner types except lamb, which we do not serve. The vegetarian menu is our default unless a retreat's real menu is known: for example a vegan menu, as on our vegan tours.
Emissions per person (kg CO2e) = number of breakfasts × breakfast factor + number of lunches and dinners × lunch or dinner factor
Guide and team
The travel, accommodation and meals of our guide and team are calculated with the same methods and added to the total of the retreat or journey, then shared between the participants.
- Travel: our team travels from Zagreb. We use a car for destinations closer than 1,000 km and a plane, plus a car or ferry to the venue where needed, for destinations further away.
- Accommodation: the team stays in a single room of private accommodation, using the 2-star factor. When the team stays in the venue itself, we use the venue's own star rating.
- Meals: the team eats the same meals as the group.
What is not included
- Travel to the destination and the teachers' own travel, because they differ for everyone. Travelers add their own journey on the report page.
- Equipment for activities such as bicycles, kayaks and yoga mats. Activities themselves use human power. Counting the equipment would need a life-cycle assessment of every item and we rarely know in advance which equipment is used. Boat trips are included through their fuel use.
- Visits to sites and parks, because national parks and nature parks have no emission data per visitor, and Croatia's national greenhouse gas inventory does not cover tourism.
- Personal waste, souvenirs and personal spending.
- The manufacture of vehicles and buildings. The factors for transport and accommodation do not include them.
Offsetting by planting trees
Offsetting does not remove the footprint of a journey. It supports projects that take carbon out of the air. We chose reforestation in Croatia through Boranka, the volunteer tree-planting campaign of the Scouts of Croatia, carried out with Hrvatske šume (Croatian Forests) and the Croatian Mountain Rescue Service. It restores land burned by wildfires in Dalmatia with native species such as downy oak, black pine, maritime pine, stone pine, cypress and shrubs. Boranka states a donation of €1.50 turns a drawn tree into a real one.
How much carbon a tree absorbs depends on the species, growing conditions and lifetime, so it cannot be stated exactly. According to figures provided to us by the Scouts of Croatia, an average tree absorbs about 12 kg of CO2 per year over its whole life. Large long-lived oaks absorb about 20 kg a year (around 2.8 tonnes over a 140-year rotation), downy oak about 15 kg, pines about 10 kg and shrubs about 5 kg. Most trees absorb the most during their first 20 to 50 years of active growth. These are estimates, not measurements.
Where the numbers come from
- Transport emission factors: UK Government GHG Conversion Factors for Company Reporting 2024, UK Government, Excel file "Conversion factors 2024: full set (for advanced users)". Worksheets: Business travel - air, WTT - business travel - air, Business travel - sea, WTT - business travel - sea, Business travel - land, WTT - pass vehs and travel - land, Freighting goods, WTT - delivery vehs and freight, Fuels. gov.uk
- Accommodation: Hotel Footprinting Tool (Croatia), International Tourism Partnership and Greenview, based on the Cornell Hotel Sustainability Benchmarking Index. hotelfootprints.org. Method: Hotel Carbon Measurement Initiative.
- Food: Our World in Data, food greenhouse gas emissions and environmental impacts of food, based on Poore, J. and Nemecek, T. (2018), "Reducing food's environmental impacts through producers and consumers", Science.
- Food waste: European Parliament, food waste figures.
- Boat fuel use: boat-fuel-economy.com, and the operating data of our catamaran partner Huck Finn.
- Flight cross-check: myclimate flight calculator.
- Model and standard: VisitScotland Holiday Carbon Calculator; Greenhouse Gas Protocol.
- Tree planting: Boranka (Scouts of Croatia, Hrvatske šume, Croatian Mountain Rescue Service). The absorption figures come from the Scouts of Croatia.
The factors in this method are from the 2024 edition of the UK Government conversion factors. We review them when a new edition is published and say here which edition we use. See the Sustainability page for a calculator you can try yourself.