What Is The Difference Between CO2 And CO2e?

difference-between-co2-vs-co2e

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

Inevitably, they are in the process of calculating their carbon footprint and have realised 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, colourless and odourless 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 vapour 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.

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 under scope, and therefore a fuller picture of an organisations 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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3 comments
François Sarran says September 13, 2018

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

Reply
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

Reply
    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/

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