How much cheese do you need to afford a house?
At Greengauge we are always looking for ways to reduce the carbon emissions that buildings are responsible for. As an industry we mostly focus on the operational energy (and associated carbon) of the building: the energy required to run the building, heating, lighting and so on. This is the basis of Part L of the regulations as well as Passivhaus. Whilst our aim is to reduce the carbon, we tend to measure performance based on energy and there is good reason for that. Energy use (rather than carbon emissions) give a much better indication of how well a building performs. Carbon emissions for energy generated vary significantly according to how the energy was generated (e.g. gas vs wind) and this varies from country to country and from day to day depending on factors such as how windy it is. However, 1kWh of energy is always 1 kWh and this is a unit which many people are familiar with. Carbon based rules can introduce more unintended consequences if the calculation does not carefully consider the way the energy supply works.
In addition to operational energy (heating, lighting etc…), we should also consider the “embodied” carbon released due to the manufacture of materials, as well as their transport, installation, demolition and disposal. Along with the energy (kWhs) required to make a product, the manufacturing process of some materials directly releases CO2 from the chemical reactions required to make the material, e.g. cement and steel. To be able to compare operational and embodied emissions we need to then shift units and start talking directly about CO2 emissions not just kWh.
However, kgs of CO2 is not a unit of measurement that most people are familiar with. We don’t necessarily understand how to value a kg of CO2 being saved from a project. As pointed out in the book ‘How bad are bananas? The carbon footprint of everything’ by Mike Berners-Lee we need to become carbon literate if we want to really address climate change.
Everyone knows that a new TV is going to cost them more than a block of cheese, and that we would have to not eat cheese for a long time if we wanted to save up for a TV
Compare this to people’s grasp on money. Everyone knows that a new TV is going to cost them more than a block of cheese, and that we would have to not eat cheese for a long time if we wanted to save up for a TV. We don’t necessarily know the exact cost of these objects and it will vary from type and brand, but we have a good feel, certainly when it comes down to orders of magnitude. But when it comes to carbon, are cheese and TVs even within an order of magnitude of each other, and if you were told 1 kg of cheese is responsible for 12kg of CO2e on average, is that a lot?
(CO2e – Carbon dioxide equivalent” is a term for describing different greenhouse gases in a common unit. For any quantity and type of greenhouse gas, CO2e signifies the amount of CO2 which would have the equivalent global warming impact)
Ultimately that figure of CO2 for cheese is ‘wrong’ along with every other number you see regarding embodied carbon, but it doesn’t matter. By wrong I mean it’s wrong in the same way you couldn’t ask how much a TV costs and get only one true number, it depends; on how it was made, where it was made and what type of ‘cheese’ it is. The absolute number doesn’t matter but a number in the right ballpark is very useful, it lets you start comparing options and understanding what is significant in looking at how we can start to reduce our carbon footprint.
To put 12kg of CO2e (1 kg of cheese) in perspective:
The average UK inhabitant is responsible for approximately 15 tonnes CO2e per year through their normal lifestyle (30 for someone in America and 3.3 tonnes for someone in China). That’s 1250kg of cheese. The average British person eats 11.7 kg of cheese a year. So roughly 140kg of CO2e, about 1% of the 15 tonnes. Now these numbers are starting to be useful, if we treated carbon the same way we treated money, we could argue that if we didn’t eat cheese for 1.5 years we would have ‘saved up’ and could ‘afford’ the carbon released in the production of a new 42’’ LCD TV (assuming we are allowed to ‘spend’ any carbon at all!).
This is not a war against cheese there are many foods worse for the environment (such as air freighted asparagus or out of season tomatoes from heated greenhouses) but out of interest if we looked at world annual cheese consumption, that is approximately equivalent to 0.25 billion tonnes of CO2.
Global greenhouse emissions are estimated at 53.5 billion tonnes CO2e. (2007 IPCC). So that is significant at ~0.25% of the world’s emissions, therefore your supermarket choices do make an impact.
Relating all this back to buildings. The RIBA 2030 challenge targets have been recently updated (and increased) for embodied carbon of a new build residential building to <645kgCO2e/m2. Taking this as a worst case scenario, the embodied carbon of a new 200m2 dwelling (a comfortable 3-4 bed house) would be responsible for 129 tonnes of CO2e. Equivalent to ~8.5 years of emissions from the lifestyle of a UK inhabitant, or over 10000kg of cheese. Better start saving.