Why are plant production processes showing negative values in the LCI "ClimateChange" even though it is not reasonable.

Question

I am working with the ecoinvent data base. When I use Inputs such different types of animal feeds, grass silage etc. I receive negative figures because of considered CO2 uptake by plants. Can I easily ingnore this elementary flow? Usually plant production result in a balanced soil carbon status, so the CO2 footprint shouldn´t be negativ eventhough some carbon is stored in the product. For animal production processes it is on the other hand often not possible to calculate this respiration losses accuratly. I even do not know this situation, while I am working with the ecoinvent data in SimaPro.

Answer 1

Hi Thorsten, when plants grow they assimilate CO2 in their biomass ... that is why e.g. rain forests serve as huge CO2 sinks (obviously). Thus it makes sense, that in ecoinvent plants (during growth) have a negative CO2 impact. The respiratory emissions e.g. during digestion by animals only occur later in the supply chain and are not considered at the point of plant production. Thus, the (mathematically) negative environmental impact will only be canceled out if you consider the entire supply chain including the release of the plant(biomass) based CO2 back into the atmosphere. But again, only looking at the growth stage of plants I think it does make sense that the impact is negative.

I hope this helps.

Comments

Hi Jonas, thank you for you answer. I understand the point but I have to mentione that for agricultural purposes the assumptions which are made are not suitable. Lets take cow milk as an example. When you prove dairy cow milk from the ecoinvent data basis processed in openlca you will get very low CO2eq figures for 1 litre of milk ~0.20kg. This is far beyond what you will find in the literature and will cause trouble in your environmental communication.
Best Thorsten

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Hi Thorsten, I agree with your comment. In a recent project for a German federal agency we manually added the respiratory GHG emissions of animals to the environmental footprint of dairy product processes in ecoinvent.

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Interesting. Can you share the references or assumptions, which have been made for calculating the respiration?

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Hi Thorsten, a bit random notes but here you go (all values simplified):

Der respiratorische CO2 Ausstoß beziffert sich laut Phillipe and Nicks (2008)  auf 4,87 kg CO2 Äquivalente pro kg Schlachtkörper Schweinefleisch.

Philippe, F.-X., and B. Nicks. 2015. “Review on Greenhouse Gas Emissions from Pig Houses: Production of Carbon Dioxide, Me-thane and Nitrous Oxide by Animals and Manure.” Agriculture, Ecosystems & Environment 199 (January): 10–25. https://doi.org/10.1016/j.agee.2014.08.015.

Der Ausstoß von respiratorischem CO2 wurde unter Annahme eines Sauerstoffumsatzes von 0.022l/min/Huhn  getroffen. Damit summiert sich der gesamte Atem-sauerstoffverbrauch bei einer Lebensdauer von 37.5 Tagen  auf 1.188 Liter (konventionell) und bei einer Lebensdauer von 81 Tagen  auf 2.566 Liter (biologisch). Weiterhin wurde angenommen, dass der CO2 Ausstoß gleich dem Sauerstoffumsatz ist. Der CO2 Ausstoß beträgt somit für ein konventi-nelles Huhn 2.19kg und für ein biologisches Huhn 4.73kg.

Müller, Rainer. n.d. “Atmung, Stoffwechsel Und Blutkreislauf.” Accessed October 12, 2018. https://www.tu-braunschweig.de/Medien-DB/ifdn-physik/atmungstoffwechsel.pdf.

Wiedemann, S. G., F. A. Phillips, T. A. Naylor, E. J. McGahan, O. B. Keane, B. R. Warren, and C. M. Murphy. 2016. “Nitrous Oxide, Ammonia and Methane from Australian Meat Chicken Houses Measured under Commercial Operating Conditions and with Miti-gation Strategies Applied.” Animal Production Science 56 (9): 1404. https://doi.org/10.1071/AN15561.

Der tägliche respiratorische Treibhausgasaus-stoß einer Milchkuh beziffert sich bei einer durchschnittlichen Milchproduktion von 28,5 kg pro Kuh pro Tag auf 12.2 kg CO2 pro Tag pro Kuh und 0,385 kg CH4 pro Kuh pro Tag (Chianese et al., 2009; Kinsman et al, 1995). Unter der Annahme, dass 28,5 kg Milch auch 28,5 Liter Milch entspre-chen, entspricht dies 0,428 kg CO2 und 0,0135 kg CH4 pro Liter Milch.

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Hi Jonas, thank you very much! By the way, are there some openLCA courses already scheduled in 2019 close to Kiel? I use openLCA in my teaching-course with ~20 students each semester and I want to deepen my knowledge about. Best, Thorsten

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I sent you an email.