Household Carbon Calculator
Introduction
Island communities are both more vulnerable to climate change and have a have a greater challenge to overcome in the transition to net zero due to their remoteness and reliance on fossil derived fuels for energy.
As the transition will require some behavioural changes, willing households have a key role to play. Changes to energy and fuel, diet, control of waste and usage of services should all be assessed. For this reason, the ICNZ Household Carbon Calculator will allow users to assess their carbon footprint based on a number of lifestyle factors and will deliver a tailored list of recommendations to help reduce their emissions.
While other household carbon calculators are available, our calculator has the benefit of being tailored to users across the three island groups in a way that others aren’t. The differences across island groups and between the islands and mainland Scotland are taken into account through the emission factors used and recommendations given.
The calculator guides users through a series of questions that are aggregated and converted to annual tCO2e in an excel spreadsheet. The basic form of calculation uses an emission factor as a multiplier. For example, if burning 1kg of coal releases 2.9 kg of CO2e into the atmosphere and your household uses two 20kg bags of coal a month on average, the calculator multiplies the estimate across the whole year and applies the relevant emission factor. In this case the coal burned would result in 1.392 tCO2e released annually.
Data Usage
The data collected from the user will only pertain to calculating household carbon emissions and returning tailored recommendations. Different lifestyle factors like diet or use of digital services are relevant to the upstream emissions of your household i.e. indirect emissions caused by consumption.
The data points gathered are :
- Property Type and Age
- Fuel/ Energy Usage
- Working Patterns (WFH)
- Personal Vehicles and Public Transport
- Diet
- Physical Goods and Services Used
- Digital Services Used
- Household Waste
- Water Usage
- Energy Efficiency/ Renewable Energy Installations
In some instances where the user doesn’t know the answer or would prefer to withhold information, the national average can be applied to allow the user to continue.
Property Type and Age
The property type, age and size allows us to estimate the embodied carbon in your house. The carbon emissions associated with the materials and construction are necessary for a full accounting of your carbon footprint. Using EPC data for Orkney, Shetland and the Western Isles, the build type, age and floor area are used to look up the relevant emission factor along with average energy cost and consumption.
Working Patterns
Hours spent working at home are checked against UK government statistics to find the average emissions per working hour caused by heating and running office equipment.
Personal Vehicles
The personal vehicles tab collects the vehicle type, size, and miles driven per month of your personal vehicle as well as vehicle type, size, and miles travelled in public transportation. It applies this data to a lookup table and multiplies the emission factor per mile from UK government statistics for your mode of transport by the number of miles driven monthly and adjusts the result to give total annual emissions. Accuracy may be impacted by variables that are not factored into calculations such as driver behaviour and regional grid mix variations (affecting BEV emissions). Similarly, the cost of using your personal vehicle is given using the data submitted and a lookup table that sources fuel costs from globalpetrolprices.com. Equivalent energy consumption is calculated using the same method to give a side-by-side comparison between battery electric vehicles and conventional fuel vehicles.
Also included in the transport questions is the option to include any carpooling undertaken by members of your household. The calculation method is the same as in the personal vehicles tab but with the distinction that the total GHG emissions are divided by the number of passengers to reflect their overall share of CO2e for each journey.
Diet
The diet tab gathers data on the dietary preferences of your household and returns an estimate for carbon emissions, energy consumption and cost based on those preferences. Predominantly plant-based diets have a far lower carbon footprint than diets that include meat due to the relative inefficiency of land and water use in farming livestock and the methane emitted by the livestock itself. As before, the data is collected for each member of your household and used in a lookup table to find the relevant emission factors, in this case sourced from ourworldindata.org. Energy consumption in based on the data from Scarborough et al. (2023). Cost is calculated using the article Comparing the Cost Of A Vegan Diet Vs. Meat-Based Diet in 2024 for high meat diets along with Scarborough et al., 2023 for medium and low meat diets.
Goods
The goods tab focuses on physical goods and excludes services. Data is input by the user for the total expenditure per year on pet food, clothes and shoes, electronics, appliances and other machinery, furniture and textiles, paper and paper products, pharmaceuticals, vehicles and maintenance and other manufactured goods. If the user is unsure about their annual spending they have the option of applying the Scottish average to the field. An assumption is made here that the proportion of household spending will remain constant for island and mainland communities. The data is multiplied by the relevant emission factor sourced from DEFRA to give annual emissions in tCO2e. Equivalent energy is calculated using the conversion factor MJ/£, which is itself calculated by dividing the the MJ/kg by the price/kg. The energy per kg has been collected from various sources and multiplied by the estimated price of goods per kg. Cost is calculated by simply summing the estimated expenditure (or Scottish averages) across all of the boxes in the goods tab.
Services
The services tab asks for spending data on non-physical purchases, including education, health personal, social care, holiday accommodation, professional services, recreation and entertainment, telecomms & postal and courier services. As with the goods tab, if the user does not have a good estimate for their spending in a particular category, the calculator allows the Scottish average to be used. Emission factors are applied using the same DEFRA dataset as for the goods tab. Services have a more complex web of upstream emission sources that makes it harder to quantify. UK conversion factors combine direct and indirect emission sources across the supply chain for each category. Energy for services provided is not returned by the calculator due to the emissions from the services being indirect, i.e. not attached to the household but the service providers. The Scottish average expenditure is sourced from the ONS family spending workbook 3, while the annual household expenditure is summed from the user inputs.
Digital Services
The digital services tab collects data on internet usage that is used to calculate upstream emissions from internet and digital service providers. The user inputs their hours spent per online activity per day, including streaming audio and video, online gaming and social media use. Values for Gigabits per hour were taken from various sources: ATT data calculator, cable.co.uk, and broadband.co.uk. The emissions are then calculated using the sum of the electricity used for streaming video for transmission (0.23 kWh/GB) and datacentres (0.002kWh/GB) as calculated by the International Energy Agency. The sum is then multiplied by the estimated GB usage per year and the kg of CO2 per kWh as per the GHG reporting: conversion factors 2023.
Energy used for transmitting data is made up of three parts. On-site energy, data transmission and offsite. Energy used onsite will already be covered by the household energy section so the calculator will exclude domestic energy. Uncertainties may arise due to the usage of UK emission factors, as data centres may be located outside the UK. Furthermore, any internet providers or digital service providers may use lower carbon electricity than accounted for in the emission factor which may lead to overestimations in terms of emissions and electricity.
Cost is calculated using broadband speed tiers (standard, superfast, ultrafast) and mobile data pricing using the formula:
Estimated Cost for Phone=[Total GB]×([% Phone]/100)×[Phone Cost (£/GB)]
Waste
The waste tab collects user data on food waste, composting and recycling of non-food waste by percentage of total consumption. Average carbon emissions per person by location are sourced from the Household waste summary data published by SEPA in 2022.
As emissions from waste are related to decomposition and disposal, there are no direct energy costs associated with them. Likewise, costs from waste disposal are not borne by the household directly so are omitted by the calculator.
Energy Efficiency/ Renewable Energy Installations
Any energy efficiency measures or renewable energy installations in the household are collected by the self-generation tab. The installations that the user already has in place will not inform the final calculations for CO2e emissions but will inform the recommendations returned by the HHCC.