Below, we discuss carbon footprints.
We outline what they are, how they are measured, how they might be used, their potential limitations, and more
First, A Reminder About The Limitations Of Carbon Footprints
Carbon Footprints Aren’t Definitive
What should be noted is that there are limitations to calculating and using carbon footprints.
They aren’t a perfect concept, or a definitive or absolute measurement that can be used for solid conclusions, or solely relied upon for major decision making
They are more a generalised tool, or an estimate only.
In a similar vein to water footprints though, they may be considered in an integrated approach to measuring greenhouse gas emissions alongside other more advanced, detailed and reliable methods of GHG tracking and calculation
static.ewg.org explains the use of carbon footprints in a similar way to what is described above:
A carbon footprint might be better used to give a general sense of the magnitude of GHGs associated with a particular product or activity, as opposed to providing a specific and absolutely certain number.
Why Carbon Footprints Have Limitations
The total carbon footprint cannot be exactly calculated for a lot of products and services because of different factors
Some of these factors might include inadequate knowledge of what makes up a footprint, a lack of data when calculating the footprint, differing production and lifecycle processes for different products and different companies and suppliers, different geographic weather and conditions in different locations, and so on.
There are different variables to account for with the above factors and other factors (like for example, the type of transport used for freight in shipping or transporting a product)
Some factors and variables will also change over time.
Different assumptions may also go into carbon footprint data.
All these things can result in different carbon footprints, depending what is being measured, what the assumptions are, what the factors and variables are, over what time period it’s being measured, and so on.
What Is A Carbon Footprint?
In general, a carbon footprint is the amount of greenhouse gas emissions that results from something.
It could be from producing something, doing something, or something else.
There’s a carbon footprint to almost everything – from different foods, to an activity like driving a car, and even for an entire country.
A carbon footprint takes into account all greenhouse gases – mainly Carbon dioxide (CO2), but also other major greenhouse gases like Methane (CH4), and Nitrous oxide (N2O)
All greenhouse gases can be combined and expressed in one unit of measurement, called CO2e (carbon dioxide equivalent)
wikipedia.org also notes that (paraphrased) all carbon sinks and carbon storage sources should be taken into account when calculating a carbon footprint
Sinks and storage effectively help reduce the built up footprint
One example of this is a city that may plant more trees as a carbon sink, and the total footprint of that city may drop as a result
CO2e Used A Common Unit To Compare One Footprint To Another
CO2e stands for carbon dioxide equivalent.
CO2e is a common unit of measurement that allows different greenhouse gases to be combined/converted into one uniform figure.
A car for example may principally emit CO2, but also emit nitrous oxide and methane in smaller amounts (all 3 are greenhouse gases). CO2e allows for combining all three gases into the one unit
The quantities of each greenhouse gas, along with their global warming potential, are both considered, and converted to one CO2e figure.
The higher the quantity and GWP of other greenhouse gases, the higher the CO2e figure.
Ultimately, this allows different carbon footprints (consisting of different quantities of different greenhouse gases) to be compared to one another.
carbontrust.com outlines this CO2e calculation in their report.
Other Units Of Measurement Used For Carbon Footprints
Emissions can be measured in different ways, such as total emissions, rate of emissions, share of emissions, per capita emissions, emissions per kWh produced, emissions per per British thermal unit (Btu), carbon intensity of a specific activity, and so on.
Similar Principles & Considerations Between Carbon Footprints & Water Footprints
It’s worth noting that many of the same principles and considerations that apply to the calculation and use of water footprints, may also apply to carbon footprints.
So, it might be worth reading this guide about water footprints.
As a summary, similar considerations that apply to both water footprints and carbon footprints include (we’ve inserted emissions or carbon as the measurement instead of water use below):
– Assessing emissions over the whole lifecycle vs individual stages
– Assessing direct vs indirect emissions
– The different types of emissions/greenhouse gases (which we listed above in this guide)
– Carbon footprints can differ for the same type of product produced in different geographic locations, or with different processes (due to different variables)
So, it’s important when looking at carbon footprints, to not only look at how the measurement was calculated, but look at exactly how and where the individual product was produced
– Carbon footprints can be imported and exported between countries
Especially between both predominantly producer countries, and predominantly consumer countries
– A carbon footprint as a tool has limitations and flaws
– A carbon footprint might still be used in an integrated approach, with other more detailed, advanced and more reliable/accurate methods of calculating emissions
– You can find carbon footprint calculators online, but carbon accounting and life cycle assessment resources also help in calculating carbon footprints
Examples & Breakdowns Of Different Types Of Carbon Footprints (What They Are Made Up Of)
Below are a few examples different types of carbon footprints, and, a breakdown of what they are made up.
We include factors like different stages of the product life cycle (from from sourcing through to waste (dumping, recycling, or re-use)), and also direct vs indirect emissions …
Vehicles
The carbon footprint of a car includes but isn’t limited to:
Sourcing of materials that make up the car and it’s parts, like it’s tires
Manufacturing of the car and it’s parts
Operating of the car
Direct emissions that come out of a car’s exhaust from the combustion of petroleum based fuel
Indirect emissions at the power plant when electricity is generated for electric cars
Upkeep of the car – washing, cleaning, servicing, repairing, modifications, and so on
The extraction/mining, shipping, refining and transport of fossil fuel based fuels to gas stations
The end of a car’s lifecycle, such as going to scrap metal
Food
The carbon footprint of food includes but isn’t limited to:
All farm level emissions, from fertilizer, pesticides, livestock (burping and passing other gases), manure, energy use
Transport to market
Processing and cold storage, and transport to retail
Emissions at the retail level, such as in supermarkets and stores (for lighting, cooling, and so on)
Emissions from consumers to and from stores, and cooking/preparing, storing/refrigerating, and disposing of, or wasting food
Might even include methane emitted at the landfill stage when wasted or lost food is decomposing.
There’s also other indirect emissions from things such as plastic packaging, glass bottles, and cartons that food can come in.
For the footprint of entire cities, you not only have to consider the direct emissions that go on within the city boundary, but also the indirect emissions that happen outside the city boundaries for things such as products that are produced elsewhere, and imported into the city for consumption.
Sectors like agriculture, industrial activity, residential and commercial, and even transport when considering electric cars, all have their own direct emissions, but also indirectly use electricity from power generation, which has an indirect emission footprint
Energy sources can emit greenhouse gases not only directly at the combustion stage, but indirectly also across the whole lifecycle of sourcing and using the energy source.
One example of this the potential for indirect methane leaks when mining oil or gas, in addition to direct emissions when burning oil or gas products when using them for energy a the operation stage
Transport (burning of fuels, or use of other energy source), homes and buildings (electricity use) and food make up a reasonable % of an individual’s carbon footprint.
Both wikipedia.org and greeneatz.com indicate this
Businesses
carbontrust.com indicates that (paraphrased) businesses might have specific footprints to measure and assess.
They list where emissions might come from under organisational, value chain, product and supply chain areas.
Some examples of emissions include from building energy use, industrial processes, company vehicles, up and down the supply and demand chain with the actions of consumers and suppliers, the complete lifecycle of the product or service itself, and raw materials.
The Impact Of Indirect Emissions In Carbon Footprints
Carbon footprints are made up of both direct emissions, and also indirect emissions
Indirect emissions can make up a much larger % of carbon footprints than direct emissions in some instances
Most of the carbon footprint emissions for the average U.S. household come from “indirect” sources, e.g. fuel burned to produce goods far away from the final consumer (wikipedia.org)
Be Aware Of Inclusions & Omissions In Reports On Carbon Footprints
Understanding Inclusions & Exclusions
It’s important to look at the inclusions and also the exclusions (omissions) of a specific carbon footprint.
You have to look to the actual report about the life cycle assessment that the calculation comes from, and check what data was included and excluded from the final report numbers.
This helps with understanding what data a footprint represents, and also helps in comparing one footprint to another.
Example Of A Carbon Footprint Report
As one example, an EWG and Cleanmetrics report outlines what was included and excluded in their data for their life cycle assessment (LCA) of the carbon footprints they provide for different foods.
You can access the report from the link in the resources list.
As a summary though, the data they did and didn’t include for the carbon footprint of different foods was (paraphrased and summarised) …
– LCAs included GHG emissions associated with the following processes:
Production and transport of “inputs,” the materials used to grow crops or feed animals …
On-farm generation of GHG emissions …
On-farm energy use (fuel and electricity, including energy used for irrigation)
Transportation of animals and harvested crops
Processing (slaughter, packaging and freezing)
Refrigeration (retail and transportation)
Cooking
Retail and consumer waste (waste before and after cooking, including served but uneaten food that is thrown away)
– Due to lack of data, the LCAs did not consider the following processes related to food production:
Consumer transport to and from retail outlets
Home storage of food products
Production of capital goods and infrastructure …
Energy required for water use in growing livestock feed …
Other Potential Limitations, Flaws & Uncertainties With Using Carbon Footprints
Towards the top of this guide, we discussed why carbon footprints may be a limited tool in some ways.
But, below we’ve included more information on why this might be the case.
List Of Potential Limitations, Flaws & Uncertainties With Calculating & Using Carbon Footprints
To summarise, some of the potential limitations, flaws and uncertainties with calculating and using carbon footprints might be:
– Emissions data isn’t fully accessible or available
– Lack of transparency or certainty with what actually happens in a supply chain or the production process
e.g. what practices have definitely been implemented
– Lack of transparency or certainty leads to assumptions being part of a carbon footprint calculation, and these assumptions could be inaccurate
– Conditions and environments for production differing around the world
e.g. in agriculture, climate, types of farmland, soil conditions, etc can vary
– Different processes and methods being used to produce different products
e.g. in agriculture, different food production systems can be used, such as factory farmed vs open range farming
– Variables in different processes
e.g. in beef production, the length of time in the feedlot might vary from farm to farm, and this impact total resources/inputs used as well as emissions and other factors.
The types of input used in farming processes, and the distance that farmed goods has to travel to processing or to market, are other examples of variables
– Uncertainties associated with IPCC emission factors (from the variability of activity data used to model specific production systems) (static.ewg.org)
What Other Reports Indicate About The Limitations Of A Carbon Footprint As A Tool
Several different reports below make comments about the limitations and uncertainties in calculating carbon footprints, and using them as a tool.
From static.ewg.org:
[Using food/agricultural products as an example] ‘Predicting GHG emissions with absolute certainty is difficult … [and] Actual GHG emissions associated with a given product will vary depending on [various factors]
In general, there is significant variability and uncertainty with respect to greenhouse gas emissions from agricultural systems. Actual emissions may vary considerably depending on particular conditions, compared to estimates
From wikipedia.org:
A recent study’s results … found that the calculation of carbon footprints for products is often filled with large uncertainties.
The variables of owning electronic goods such as the production, shipment, and previous technology used to make that product, can make it difficult to create an accurate carbon footprint
From theguardian.com:
The dilemma (in measuring a carbon footprint) is that it is also impossible to pin down accurately.
[We don’t know how] the impact of our bananas compares with the impact of all the other things we might buy instead unless we have some way of taking into account the farming, the transport, the storage and the processes that feed into those stages.
Do the best job you can, despite the difficulties, of understanding the whole picture … make the most realistic estimates that are possible and practical, and be honest about uncertainty [in estimations and stats].
Some Of The Different Ways To Calculate Or Express A Carbon Footprint
Some different ways to calculate or express a carbon footprint might be:
– Carbon emissions per kilowatt hour of electricity
We use this for different energy sources for example
– Carbon emissions per passenger, per mile or kilometre travelled
With cars in particular, we can measure CO2e per kilometer or mile, but also per passenger in the vehicle (as ride sharing or public transport can be more efficient per passenger)
These measurements can also be combined into one measurement
– With food, CO2e can be measured in terms of CO2 per pound of food, per gram of protein, per gram of fat, per calorie, per dollar of economic value produced, and more
– In general for different products and things, emissions might be measured in total emissions annually, emission intensity, and also other measurements
How To Calculate Carbon Footprints
There’s various online carbon calculators that might provide different ways to calculate carbon footprints.
Reports like carbontrust.com also have a carbon foot printing guide to help with calculating carbon footprints
Carbon accounting is another way to calculate and track footprints
A Note About Transport Of Goods In Relation To Carbon Footprints
Some reports may indicate that locally produced or locally grown products and services have a lower footprint than those that aren’t locally produced or grown.
This might not always be the case.
Potential reasons for this might include:
– The type of transport used to move a product matters
In some instances, sea freight can be much more eco friendly than road freight in terms of emissions
… there can be less GHG emissions manufacturing in China and sea freighting to an Australian city port, rather than manufacturing in Australia and road freighting within Australia (whogivesacrap.org)
So, longer distances do not always lead to more emissions. The type of freight matters.
For example, a longer sea freight trip from overseas might produce less emissions than a shorter road freight trip locally.
Distance, freight type, freight packing efficiency, and freight fuel used might be considerations
Ultimately, Carbon Footprints Should Be Calculated Individually
The above information demonstrates that carbon footprint should each be calculated individually/separately for each individual thing (like a product or service), taking into account the different individual factors that make up that product or thing.
Other Resources On Carbon Footprints
Below are a range of different resources on carbon footprints:
Large Scale Carbon Footprints
General Solutions To Reducing Carbon Footprints
Countries
Countries With The Largest Carbon Footprint
Cities
What To Know About City Carbon Footprints
Cities With The Largest Carbon Footprints
Industries/Sectors
Industries & Sectors With The Largest Carbon Footprint
Individual People
Sustainable Carbon Footprint To Aim For For Individuals
Effective Ways For An Individual To Decrease Their Carbon Footprint
Everyday Things
Carbon Footprints Of Everyday Things
Energy Sources
Carbon Footprint Of Different Energy Sources
Transport
Which Form Of Transport Has The Highest Carbon Footprint
Foods
Foods With The Largest Carbon Footprint
How To Decrease The Carbon Footprint With The Foods You Eat
Sources
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19. https://www.transit.dot.gov/sites/fta.dot.gov/files/docs/PublicTransportationsRoleInRespondingToClimateChange2010.pdf
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25. https://www.carbonfootprint.com/energyperformancecorp.html
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28. https://www.carbonfootprint.com/plastic_waste.html
29. https://support.au.whogivesacrap.org/article/37-limiting-emissions
30. https://www.epa.gov/greenvehicles/greenhouse-gas-emissions-typical-passenger-vehicle
31. https://www.carbontrust.com/resources/carbon-footprinting-guide
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