What Is A Carbon Footprint?

A carbon footprint is generally the amount of carbon or greenhouse gas emissions that result from something.

There’s a carbon footprint to almost everything – from different foods, to an activity like driving a car, and even for an entire country.

In this guide, we outline in greater depth what makes up a carbon footprint, how it’s measured, how it might be used, and more.

Summary – What Is A Carbon Footprint

A carbon footprint is simply the carbon emissions that result from producing or doing something

Food, transport, electricity, individuals and whole countries have carbon footprints

Carbon footprints are typically expressed in terms of CO2e

CO2e stands for CO2 equivalent, and is a way of converting quantities of other greenhouse gases like methane for example, into one unit so that all greenhouse gas emissions can be compared against each other, and so there is one common unit of foot printing

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

In addition to emissions, carbon footprints may also take into account any carbon sinks or storage that may reduce the final 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

There’s also different ways to measure or express the carbon footprint for different things

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)

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

The principles and considerations that apply to carbon footprints are very similar to the ones that apply to water footprints, and we have listed them below in this guide, and linked to a resource on water footprints so you can read further into them

A few key considerations are direct vs indirect emissions, and emissions across a whole product/service lifecycle (lifetime) vs emissions across one stage of a lifecycle

When looking at a carbon footprint, be sure to look at the lifecycle assessment report that led to it, and look at the inclusions and omissions of data. It helps in comparing footprints, and getting an idea of how accurate a footprint might be

In addition to online carbon calculators, lifecycle assessment reports and carbon accounting can help with putting together carbon footprints

What is worth noting about carbon footprints is that they are a very general tool/measurement only

Carbon footprints have limitations and drawbacks in the way they can be put together, and we have detailed what these are in the guide below

An interesting not about transporting goods and services is that 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

On a society wide scale, some sources indicate that population size, economic output (and industrialization), rate of consumption, and the type of energy source used (fossil fuel vs cleaner fuels), can all significantly affect a country’s carbon footprint

First, A Reminder About Carbon Footprints

What should be noted is that there are limitations to calculating and using carbon footprints.

They aren’t a perfect concept, or a definitive measurement.

The total carbon footprint cannot be exactly calculated for a lot of products and services because of inadequate knowledge, a lack of data, differing production and lifecycle processes, different geographic weather and conditions, and so on.

At each stage or in different geographic locations, there are different variables and factors to account for (different types of freight/transportation used is one variable) to account for.

Some factors and variables will change over time

Different assumptions may also go into carbon footprint data

All these things can change to different results for 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.

So, carbon footprints are only a general tool for general discussion about emissions.

They are not a definitive or absolute measurement that can be used for solid conclusions, or solely relied upon for major decision making

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:

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.

What’s A Carbon Footprint?

In general, a carbon footprint is the amount of greenhouse gas emissions that results from producing something, or doing something.

It takes into account all greenhouse gases – Carbon dioxide (CO2), Methane (CH4), Nitrous oxide (N2O), Hydrofluorocarbons (HFCs), Perfluorocarbons (PFCs) and Sulphur hexafluoride (SF6).

Carbon dioxide might be considered the main greenhouse gas, but methane and nitrous oxide also receive attention

wikipedia.org also notes that ‘ … all relevant sources, sinks and storage [i.e. carbon sinks and storage] within the spatial and temporal boundary of the population, system or activity of interest [should be taken into consideration]’

CO2e Used A Common Unit To Compare All Greenhouse Gases

It can be expressed as solely the carbon dioxide emissions, or, as CO2e, which stands for carbon dioxide equivalent.

CO2e is a common unit of measurement that allows different greenhouse gases to be compared to one another.

Quantities of other greenhouse gases can be converted to CO2e, and this allows one common unit to see how many units of carbon dioxide another greenhouse gas represents.

The conversion is based on global warming potential (GWP100 – the 100 year GWP potential) of the other greenhouse gas – the higher it’s global warming potential above carbon dioxide, the higher the CO2e conversion number will be.

So, the CO2e calculation is essentially – quantity of gas x it’s 100 year GWP.

The calculation works because GWP is based on how many times more potent each gas is than carbon dioxide, with carbon dioxide being the base number at 1.

carbontrust.com outlines this calculation in their resource.

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 & Consideration 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, also apply to carbon footprints.

So, it’s worth reading this guide which outlines those things in regards to water footprints, and applying them to what you read about carbon footprints

As a summary, similar considerations that apply to both water footprints and carbon footprints include:

Emissions over a whole lifecycle vs individual stages

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)

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, and should be looked at and used as such

A carbon footprint might be used in an integrated approach, with other more detailed, advanced and more reliable/accurate methods of calculating emissions

A carbon footprint is a tool like a water footprint or land footprint, but is calculated to help address a specific issue better i.e. climate change

You can find carbon footprint calculators online, but carbon accounting and life cycle assessment resources also help in calculating carbon footprints

Makeups Of Different Carbon Footprints – Examples, & Breakdowns

Below are a few examples of what makes up the carbon footprint of different products and things.

We include factors like different stages of the product life cycle (from from sourcing through to waste (dumping, recycling, or re-use)), and 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 – like for example emissions that come out of a car’s exhaust from the burning of fuel. This can be considered direct emissions

Upkeep of the car – washing, cleaning, servicing, repairing, modifications, and so on

Emissions from petroleum for some cars, and emissions from electricity source for electric cars

The extraction/mining, shipping, refining and transport of fossil fuel based fuels to gas stations

The end of use of a car, 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 farting), 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

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.

Entire Cities

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.

Entire Industries And Sectors

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

Different Energy Sources

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

Individuals

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 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

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)

The Carbon Footprints Of Different Foods, Products & Things

You can read this guide which outlines the carbon footprints of foods, products and everyday things.

Be Aware Of Inclusions & Omissions In Reports On Carbon Footprints

An individual carbon footprint calculation may include, but also omit specific data.

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.

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 …

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 …

Limitations, Flaws & Uncertainties With Using Carbon Footprints

Using a carbon footprint as a definitive measurement has clear limitations and flaws.

In most cases, a complete carbon footprint cannot be exactly calculated because of various reasons such as:

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)

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]

Again from static.ewg.org:

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].

– theguardian.com

Greenhouse Gas & Carbon Footprint Calculators

You can calculate carbon per kilowatt hour of electricity with:

Emission rates of different energy sources (wikipedia.org)

You can calculate carbon per mile or kilometre of a standard vehicle, or other modes of transport with:

Greenhouse gas emissions of the typical passenger vehicle (epa.gov)

Pounds of CO2 per passenger mile (transit.dot.gov)

Environmental impact of transport (wikipedia.org)

There’s also general guides on how to calculate the GHG emissions of products:

Carbon footprinting guide (carbontrust.com)

A Note About Transport Of Goods In Relation To Carbon Footprints

What is generally assumed about carbon footprints by many sources is that locally produced or grown products and services are better (or have a lower footprint).

This is not always the case:

The type of transport used to move a product matters – sea freight can be much more eco friendly than road freight in terms of emissions.

Just as one example, 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, this goes to show that presumptions can’t be made, and each carbon footprint must be calculated individually, and specifically looking at each step of the entire process that sources, produces and delivers a product or service to market (and even the consumption and disposal or re-use stages if you want to go that far).