I'm doing a project and looking at one of my scholarly resources, it says that

The carbon footprint per kilogram protein of plant-based substitutes was found in the range of 6–17 carbon dioxide equivalent (CO$_2$-eq) kg$^{−1}$...

I want to compare it to the greenhouse gas emissions to a typical passenger vehicle, which is about 4.6 metric tons of carbon dioxide per year according to the EPA. But I have no idea what (CO$_2$-eq) kg$^{−1}$ means.

  • 1
    $\begingroup$ This seems to be poorly expressed. A larger context might shed more light on it; you may want to update the question accordingly. The way I as a lay person read this, is that the production of 1kg of plant-based protein leads to 6 to 17 kg of CO₂ equivalent emissions. Because not all climate-relevant emissions are CO₂ (e.g. methane, nitrous oxide), the non-CO₂ emissions are converted into equivalent CO₂ emission for ease of comparison. This is done by applying a factor based on climate impact (?? not sure about the details), where conversion factor for methane is 25 and for nitrous oxide 298. $\endgroup$
    – njuffa
    Nov 15 '20 at 7:29

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