What Is The Difference Between CO2 And CO2e?


Many of our readers often ask, what is the difference between CO2 and CO2e?

Usually, they are in the process of calculating their carbon footprint and have realized that the emission factors that they are using are expressed as CO2e.

This article outlines the difference between CO2 and CO2e.

Difference between CO2 and CO2e

Carbon dioxide, or CO2, is a natural, colorless, and odorless greenhouse gas that is emitted when fossil fuels (i.e. natural gas, oil, coal, etc.) are burnt.

It is the most prevalent greenhouse gas after water vapor and has therefore become the proxy by which we measure greenhouse gas emissions.

However, carbon dioxide is only one of many greenhouse gases that are emitted when humans undertake certain activities. Other greenhouse gases are methane, nitrous oxide, and ozone – all of which occur naturally in our atmosphere.

CO2e Includes Other Greenhouse Gases

To take into account the emission of other greenhouse gases when calculating the level of greenhouse gas emissions, scientists have devised an equivalent measure – CO2e (which literally means carbon dioxide equivalent).

CO2e allows other greenhouse gas emissions to be expressed in terms of CO2 based on their relative global warming potential (GWP).

CO2 has a GWP of 1, methane has a GWP of approximately 25 (on a 100-year time horizon). In other words, for every 1 tonne of methane (CH4) emitted, an equivalent of 25 tonnes of CO2 would be emitted.

In this way, we can express greenhouse gas emissions as an equivalent of CO2 using the GWP principle.

So next time you see a carbon footprint expressed in terms of CO2e, you can know for sure that all greenhouse gases have been included for each activity in scope, and therefore a fuller picture of an organization’s impact has been captured.

Note: Most greenhouse gas emission factors are expressed as CO2e. This means you don’t need to make the conversion from methane GWP to carbon dioxide GWP.

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Leave a Comment:

François Sarran says September 13, 2018

Why not a word on the correspondance between the two: How many C in a CO2e ?

Todd says October 11, 2018

I am finding it impossible to get a current ppm for CO2e. Please tell me why CO2e is rarely used these days. As all new articles refer only to CO2, am I to assume “all radiative gases are NOT accounted for” in the current ppm of approximatley 407 ppm
CO2. And, if the value of “e” a decade ago was published to be 20% over CO2 what is it today given the last decade of increased water vapor and the increase of ESAS methane per the work of Shakova/Semiletov, and, permafrost releases per the work of Romanovsky and others.

I have become very sceptical of media publications on “where we are today” vis a vis total heat forcing ppm when that damn little e is missing.

Also, what was the original date used for “pre-industrial” to present when discussing temperature increases in C? I thought it was 1780 or roughly 200 years. Today several baseline dates are used which of course alters the amount of increase. The latest report from Incheon, K. Was 115 years.

Thank you so much. I have asked several these questions of well know earth scientists and no one has responded. Todd Anderson

    Mark Whitman says October 11, 2018

    Hi Todd, appreciate your frustration on this, especially since no earth scientists are responding to your query. Unfortunately our environmental correspondent has left us so we don’t have the internal expertise to give you a solid answer. This article get’s quite a bit of traffic so hopefully another reader can provide some clarity. Otherwise I recommend contacting a few academic institutions that specialise in climate change – UEA comes to mind: https://www2.uea.ac.uk/

Mike says September 24, 2019

To Todd and François
I must say it is apparent the article above and any and all information from municipalities and evironment offices in many communities completely misunderstood the role of GWP.

P is potential, ergo, not a factual amount but a rating system for comparison.

There is NOT CO2e in the atmosphere as CO2e is not a molecule but a mathematical attempt to compare two different factors.

Imagine if you will, how many kJoule energy you receive from burning petrol for a vehicle.
Compare this to burning LPG and evaluate how much LPG you need to burn to produce the same amount of energy.

The relation between the two is the “equivalent” in “CO2e”.
It does not imply that there is or is no CO2 in a particular GHG (green house gas) but that it allegedly excerpts the same level of energy when released in the atmosphere.

It is not a physical product. It is a unit.

The question of how many C there is in CO2e is thus equivalent as to asking
“How many apples fits in a banana crate”.

    Tim Zorc says April 12, 2021

    Make, great response. I have a few questions I would like to run past you. Reach out to me on LinkedIn. Thanks Tim

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