Small Steps uses the most recent information from the UK government to calculate the carbon emissions of individual modes of transport.
Small Steps probably is not the most accurate carbon calculator out there, as it’s limited by the open-source (or inexpensive) data available to the average developer. That said, its value is in its simplicity because we believe that global warming will not be solved with overly-complex solutions but by the work of governments combined with the change in awareness and actions of individuals. It’s not the whole solution, but it’s a small step.
We chose to measure this in kilograms of carbon dioxide equivalent, or CO2e, which covers all the greenhouse gases that contribute to climate change. The final amount provided to the user is the emission for their journey as a single passenger - the government figures provide average emissions per passenger-km for large passenger vehicles. We round this number to two decimal places.
Below is a breakdown of the figures and assumptions we used to make our calculations.
We assume a medium size (1.4 litre - 2.0 litre) car with a petrol engine. The amount will be higher for diesel engines and lower for hybrid and electric vehicles.
We calculate the emission of the journey as follows:
Distance (metres) x 0.19228 kg CO2e (per passenger km) / 1000
We assume that the bus in question is a coach. The amount will be higher for local buses.
We calculate the emission of the journey as follows:
Distance (metres) x 0.02779 kg CO2e (per passenger km) / 1000
We assume that the train in question is a national train. The amount is slightly lower for international trains and roughly equivalent for light rail, trams, and underground trains.
We calculate the emission of the journey as follows:
Distance (metres) x 0.04115 kg CO2e (per passenger km) / 1000
We were unable to obtain accurate data for the distance of flights in the UK, so we used an ‘as-the-crow-flies’ number to provide us with a distance in metres.
We assume that the plane is a domestic UK flight, an average passenger (the average of economy, business and first classes for UK domestic flights), with radiative forcing included (the non-CO2 effects of aviation such as water vapour and contrails).
The amount is lower for short-haul (to/from the UK, typically Europe), long-haul (international to/from the UK), and international (international to/from non-UK) for average and economy passengers. The amount is slightly lower for short-haul business class passengers. It is considerably higher for short-haul, long-haul, and international business and first-class passengers.
We calculate the emission of the journey as follows:
Distance (metres) x 0.25493 kg CO2e (per passenger km) / 1000
We decided to provide an equivalent of the journey’s emissions in real-terms because raw numbers aren’t very appealing or understandable; we decided to provide the raw number and the number of kettles you would have to boil to produce the same amount of CO2e.
We calculated the number of kettle-boils as follows:
Emissions (kg CO2e) / 0.015kg CO2 (emission per kettle-boil)
The primary aim of Small Steps is to raise awareness of the carbon emissions associated with travelling, but we have also linked to a carbon-offsetting site. The Woodland Trust allows you to donate money to contribute to tree-planting schemes that will help to off-set the impact of your journey.