Carbon Footprint

How to Calculate a Carbon Footprint

A carbon footprint is calculated by adding up the lifetime sum of all greenhouse gas emissions from a given entity.

Taking into account the differences in GWP (global warming potential) for each gas, we can estimate an entity's carbon footprint in CO₂e (carbon dioxide equivalents). CO₂e is much more accurate than measuring CO₂ because it takes into account all greenhouse gases, not just CO₂. Several websites can be used to estimate your own carbon footprint, including this one provided by the United States Environmental Protection Agency.

Carbon Footprint Causes

There are numerous causes of increased greenhouse gas emissions, such as the burning of fossil fuels, agricultural practices, cattle farming, and more. We will go over these causes in greater detail below.

Carbon Footprint of Food

On a global level, livestock contributes approximately 7.1 gigatonnes of CO₂ to the atmosphere annually, with beef contributing the greatest amount (Fig. 1) (Table 1). Most of these emissions come from two sources - land conversion/destruction of habitat to make way for cattle grazing, and from cattle flatus. In terms of dietary patterns, it has been found that, unsurprisingly, people who eat a very large amount of meat on average contribute the largest dietary CO₂e daily, at over 7 kg CO₂e, and vegans contributed the least, at less than 3 kg CO₂e.

Table 1: Food items by kg CO₂e per kg of food.

Carbon Footprint of Vehicles (Including Electric Cars)

Vehicles contribute a very large amount of greenhouse gases to the atmosphere, though the amount contributed differs depending on the type of vehicle driven and the type of fuel used. It is estimated that the average vehicle produces 4.6 tonnes of CO₂ every year! In the European Union, over 60% of vehicle-based greenhouse gas emissions come from cars, followed by larger, heavy-duty trucks at more than 25%. The lowest contribution comes from motorbikes, at a mere 1% of the vehicle-based total.

Electric cars can reduce the vehicular carbon footprint drastically, but they do not remove it entirely. In the US, for example, it was found that using an electric car exclusively results in a little over a third of the CO₂e emissions compared to those generated by a petrol-powered vehicle (Table 2).

Another form of vehicular travel that has a major impact on your carbon footprint is air travel. Indeed, for people who travel by air frequently, the largest contributor to their individual carbon footprint (outside of whether they choose to have kids or not, more on that later) is likely to be related to travelling by plane. On a global scale, however, air travel only amounts to around 2.5% of the total carbon footprint. This is largely due to economic inequalities that result in the majority of humans being unable to afford frequent air travel.

Table 2: CO₂e emissions by vehicle type in the US.

Carbon Footprint of Emails

We may not often think about it, but the electronics we use daily produce greenhouse gases. From electric ovens to video game consoles to even the internet! Residential electricity use contributes significantly to the CO₂e in developed countries, particularly the electricity used to power indoor climate control in the form of cooling and heating.

Even using a smartphone contributes to your carbon footprint, primarily due to its manufacture, less so its actual use. The same is true for laptops, of which nearly 80% of CO₂e comes from its manufacture and only 20% from its use over a three-year average. Perhaps one of the most surprising sources of CO₂e is the use of email! Yes, every single email you send has an amount of CO₂e "attached" to it (albeit extremely small)! Individual emails are estimated to contribute anywhere from 0.03 grams to 26 grams of CO₂e, which is very small. Yet, since over 300 BILLION emails are sent annually from roughly 4 billion internet users, the amount contributed is much larger than you may expect. However, even at this level, email's contribution to the worldwide total CO₂e is tiny, being well under half of a single percent, and the use of email is vastly superior to sending physical mail in terms of carbon footprint.

Average Carbon Footprint UK

On a global scale, anthropogenic CO₂e amount to around 50 gigatonnes annually and the average citizen contributes 6.5 tonnes to that total. The average citizen in the United Kingdom contributes around 6.8 tonnes annually, so slightly higher than the global average. Citizens of the United States contribute an average of 18.4 tonnes per person, while the citizens of Brunei contribute the most, at around 38.8 tonnes (Table 3).

In terms of total emissions, rather than per person, China has by far the largest carbon footprint, at 11.7 gigatonnes of CO₂e annually, followed by the US at 5.8 gigatonnes and India at 3.4 gigatonnes. Combined, these three countries account for more than half of all CO₂e emitted globally (Table 4). Much further down the list is the UK, at around 0.4 gigatonnes of CO₂e.

Table 3: Countries by tonnes of CO₂e per person.

Table 4: Countries by gigatonnes of CO₂e.

Carbon Footprint Examples

Since looking at the total carbon footprint of an individual is time-consuming and involves more variables than we can provide here without it getting too complex, let's instead look at five different individuals' yearly travels.

Traveller #1: 12.55 tonnes CO₂e annually

Traveller #2: 22.47 tonnes CO₂e annually

Traveller #3: 16 tonnes CO₂e annually

Traveller #4: 6.35 tonnes CO₂e annually

Traveller #5: 46.6 tonnes CO₂e annually

Did you guess correctly? As you can see, business class travel, combined with a job that requires frequent commutes, adds significantly to an individual's carbon footprint. Also, you may notice that remote work diminishes levels significantly, even for a person that took a very long roundtrip flight (from the USA to Australia!) This may make you think about how much of a positive impact on the environment the popularity of exclusively remote work has become in the wake of the COVID-19 epidemic.

How Can We Reduce our Carbon Footprint?

There are several things an individual can do to reduce their carbon footprint.

As shown above, the vehicles you drive and the food you eat have a large impact on greenhouse gas emissions. Changing to a hybrid or an electric vehicle can help some, though choosing to use public transportation and eschewing vehicle ownership entirely is much better. Note that switching cars when your old car is still functional (and safe!) increases greenhouse emissions significantly since the CO₂e from car manufacturing are really high.

In terms of diet, the less meat-based your diet is, the better. Choosing to remove beef from your diet entirely can be particularly helpful, though eating an entirely plant-based vegan diet is best.

Other things you can do to reduce your carbon footprint related to food include eating food that is in season, especially regional food, since this avoids the CO₂e of long-distance food transportation.

On top of this, you can also try avoiding too many long flights (such as transatlantic flights), using more sustainable forms of energy (such as solar), recycling, heating your house in winter to a slightly lower temperature, taking colder showers, air-drying your clothing, etc.

Hopefully, you now know more about carbon footprints. Maybe you could even calculate your own!