Units used when talking about CO2e

Hi, I’m relatively new to this community, so please excuse me if I ask something that is already obvious to everyone here.

When we are talking about embodied carbon are we all talking in metric/SI units? I see mostly references to kg CO2e, and EPDs seem to refer to kg, m² and MJ (although sometimes they are for products described in inches). Is this always the case?

Is there some kind of consensus, or are people talking about different things depending on where they live?

Hi Lloyd, I think the differences come from where the reference or test was completed.

The United States use Imperial, while most of the world use the metric system. I find it easier to work with kg so I don’t get confused between tonne and ton. I don’t think it matters which system you use, as long as all references are in one unit or converted to that unit. You cannot use two different unit standards interchangeably.

Hi Lloyd, The units are driven by Product Category Rules (PCR) which state that all GWP numbers need to be expressed in kg of CO2 eq / metric unit of material. For instance concrete, all EPDs have to be expressed in kg of CO2 eq / m3 of concrete. Although metric is also required in the USA, one can reflect their concrete GWP in kg of CO2 / yd3 of concrete in addition to the required metric.
Hope this helps.

Thanks, very useful response.

It led me to www.environdec.com which says: “Product Category Rules (PCR) are documents that provide rules, requirements, and guidelines for developing an EPD for a specific product category. They are a key part of ISO 14025 as they enable transparency and comparability between EPDs.” I’ll look further and see if I can find a summary.

Wikipedia says “Global harmonization of PCR and EPD standards remains a challenge.”

Is there consensus on where to use CO2 eq vs CO2e?
Or are they understood as interchangeable?

I thought these were the same thing? The e and the eq both mean “equivalent”. GWP = 1 CO2e
For other gasses it’s my understanding that this refers to average GWP impact after 20 years as compared to CO2. Some gasses have short lifetimes (Methane is 12.4 years) and some long. https://en.wikipedia.org/wiki/Global_warming_potential

Hi Lloyd,

Most LCA data is GWP100, which evaluates the impact of other greenhouse gasses relative to CO2 over a 100 year time horizon. It is rare that GWP data looks at the 20 year time horizon, unless it explicitly states that it is GWP20.