August 15, 2022
Written by
Mike Paul

Decoding GHGs, carbon, CO₂, & CO₂e

As procurement is increasingly tasked with delivering on enterprise sustainability commitments, the function needs to get up to speed quickly with sometimes confusing terms used for emissions counting. Here, the Vizibl team breaks down the difference between some of the common terms we tend to use interchangeably.

There are lots of terms that get used in the sustainability industry all the time. You’ve probably heard all of them used at one point or another. Often they’re used entirely interchangeably. 

Greenhouse gases, carbon, CO₂, and CO₂e, however, are not the same thing, and at this point, with emissions needing to peak by 2025 if we’re to have any hope of keeping within the 1.5°C warming limit suggested by the IPCC, using the right language is a fundamental step towards successful Supplier Collaboration and Innovation on sustainability-related projects.

With that in mind, below is a brief explanation of all these terms, and where you should use them when putting together an emissions reduction programme with your suppliers on the Vizibl platform.

Emissions terms

Greenhouse gases (GHGs)

A greenhouse gas (or GHG for short) is any gas in the atmosphere that absorbs heat, and thereby keeps the planet’s atmosphere warmer than it otherwise would be. 

While GHGs do occur naturally in the Earth’s atmosphere, human activities like the burning of fossil fuels are increasing the levels of GHGs, which we are seeing contribute to climate change. The Kyoto Protocol – an international treaty for controlling the release of GHGs from human activities – recognises seven GHGs as contributing to the warming of Earth’s atmosphere, all with different ramifications (but more on that later!):

The Kyoto Gases – GWP*

Carbon dioxide (CO₂) – 1
Methane (CH₄) – 25
Nitrous oxide (N₂O) – 298
Hydrofluorocarbons (HFCs) – 124 - 14,800
Perfluorocarbons (PFCs) – 7,390 - 12,200
Sulphur hexafluoride (SF₆) – 22,800
Nitrogen trifluoride (NF₃) – 17,200

*Different GHGs can have different effects on the Earth's warming. Two key ways that these gases differ from each other are their “radiative efficiency”, or their ability to absorb energy  – and how long they stay in the atmosphere, also known as their "lifetime”. Both these factors come together to give a gas its total Global Warming Potential, or GWP.

CO₂ is the “baseline” gas for calculating GWP, since it’s the dominant greenhouse gas in terms of global emissions from human activity. It therefore has the index value of 1, and the GWP for all other GHGs is the number of times more warming they cause compared to CO₂. 

As you can see from the table above, methane causes 25 times more warming over a 100 year period compared to CO₂. Even though there’s significantly less methane in the atmosphere than CO₂, and it only remains there for about 10% of the time, you can quickly see how even a relatively small increase in methane emissions from human activity could sharply alter the balance of the gases in Earth’s atmosphere.


Easily the most commonly used word when talking about supplier sustainability, “carbon” is a shorthand that many people use in place of carbon dioxide, or more likely when they are actually referring to CO₂e, greenhouse gases in general, or a company’s emissions as a whole. You’ll hear the phrases “decarbonising the supply chain” or “low carbon economy” doing the rounds quite a lot in the world of sustainability, and while they aren’t entirely wrong to say, they’re at best imprecise and at worst incorrect, ambiguous, and confusing.

In simple terms, carbon is a chemical element which is present in many gases and compounds. In more grandiose terms, it’s the foundation of all life on Earth, without which we wouldn’t have DNA or proteins. In the world of supplier sustainability, as we’ve briefly covered above, “carbon” is used as a quick way to describe greenhouse gas emissions. This isn’t necessarily wrong – you could absolutely use an equation to calculate the actual amount of carbon present within a given amount of CO₂ – but would be wrong if you were talking about a GHG that doesn’t actually contain carbon such as methane. 

Having said that, the concept of “removing carbon” from the atmosphere (and related terminology) is something that forests, for example, do actually effect. As most people probably know, trees take in carbon dioxide and let out oxygen. The bit we didn’t necessarily learn at school is that, of course, that also means that trees store (or sequester, if you prefer) carbon – in their trunks, branches, leaves and roots. This is why forests and other vegetation, as well as soils and our oceans, are vital carbon sinks that must be protected. 

Sometimes saying “carbon” is right, and sometimes it’s wrong. It depends on what exactly you’re talking about. However, the main takeaway from here is that carbon is often used as a shorthand for what we’re going to talk about next: CO₂, and CO₂e.

Carbon dioxide

Carbon dioxide (CO₂) is the most common GHG emitted by human activities in terms of the quantity released and the total impact on global warming. One part carbon and two parts oxygen, “CO₂” is sometimes used as a shorthand expression for all greenhouse gases - however, this is incorrect, and can cause confusion.

A more accurate way of referring to a number of GHGs collectively is to use the term “carbon dioxide equivalent” or “CO₂e” (explained below).

CO₂ is considered the most dangerous greenhouse gas due to its potential lifetime of up to 1000 years. Its prevalence in the atmosphere due to human activities has increased some 45% since the start of the Industrial Revolution. However, its importance should not diminish the presence of the other GHGs, and all of them should be considered if a company is formulating a truly holistic emissions reduction strategy, both within its own operations and further afield in its supply chain. Greenhouse gas inventories are more complete if they include all GHGs and not just CO₂.

Carbon dioxide equivalent (CO₂e)

“Carbon dioxide equivalent” or “CO₂e” is a term for describing all the different greenhouse gases into 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. 

This technique helps especially with standardising sustainability reports; if a company was to report on each individual greenhouse gas, it would be far more difficult to interpret a true impact on the environment. “CO₂e” is very likely to be used in Supplier Sustainability Management reports to express your total number of GHG emissions, so it’s a good term to be well versed in before you get started.

To calculate CO₂e, you can simply multiply a GHG by its GWP. So, if 1kg of methane is emitted, this can be expressed as 25kg of CO₂e (1kg CH4 * 25 = 25kg CO₂e).

Alternative expressions of CO₂e

Sometimes, CO₂e is prefaced by “t” for “tonnes of carbon dioxide equivalent” – stylised as tCO₂e. The same goes for kilograms: kgCO₂e. These are used similarly to the way we might write “240k” instead of “240,000” – it allows sustainability reporting teams to shorthand what would otherwise be very long, difficult to digest numbers.

Also, on your travels around supplier sustainability, you might encounter the term MtCO₂e, although this is an expression that you will need to get context for. Unfortunately, the “Mt” portion of MtCO₂e could stand for metric ton, megatonne, or million tonne – although those last two are technically the same. It’s no wonder people new to the topic are often confused by all the terminology they encounter.

It is also worth noting that “CO₂e” is occasionally expressed as “CO₂eq”, or even “CDE” (carbon dioxide equivalent), although they are unusual. If spotted, these terms can be used interchangeably.

GHG emissions and the supply chain

As the Sustainable Procurement movement grows, it becomes especially important for procurement professionals to get a clear handle on the key terms used for emissions reporting and reduction. 

This is because the vast majority of enterprise emissions fall under the procurement function’s remit; CDP’s own data from reporting companies shows that large organisations’ scope 3 “value chain” emissions are on average 11.4 times greater than that of their own operations. 

This is significant, as it means that most of our ability to impact overall emissions figures sits not within our own “four walls” but within our supply chains. As the function that sits at the interface between the business and its extended ecosystem, procurement has a vital role to play in any supplier sustainability programmes. 

Vizibl Supplier Sustainability Management

With many businesses looking to their suppliers to effect the fastest, most impactful change, especially when it comes to reducing GHG emissions, a huge opportunity arises for procurement and supply chain leaders to drive progress on these key business priorities. 

But just getting an accurate feel for supplier sustainability performance is difficult, let alone closely collaborating with supplier stakeholders to set reasonable targets and reduce emissions. And, given the amount of data and capacity needed for successful supplier collaboration at scale, it's no surprise that 78% of CDP responding enterprises aren't engaging their suppliers on sustainability.

To aid procurement and its colleagues in advancing their sustainable procurement programmes, we built Vizibl Supplier Sustainability Management. Expanding our platform’s sustainability capabilities, this module enables you to quickly visualise your value chain’s aggregated sustainability scores using the latest CDP data, and set a roadmap of supplier improvement targets over time.

When combined with Vizibl’s unique and powerful set of Supplier Collaboration & Innovation tools – Supplier Relationship Management, Supplier Collaboration Workspace, and Innovation Hub –  this module allows for fully centralised management of supplier sustainability targets, objectives, and results. 

To learn more about how Vizibl is helping large organisations deliver on their strategic sustainability goals, visit Vizibl Supplier Sustainability Management.

Subscribe to read more like this ...

Related articles

Supplier Collaboration - dividerSupplier Collaboration - divider

Ready to build real supplier relationships that impact your organisation?

Contact us