Globally, passenger transport by road (cars, buses, motorcycles, etc.) contributes 45.1 % of CO2 emissions. For this reason, “greener” alternatives to the already established means of transportation have been sought for several years. The focus has been strongly on electric cars and hydrogen-powered vehicles.[1] Completely disregarded was probably the most practical and definitely the cutest form of transportation of all: APPA the Sky Bison.
The goal of this article is to clarify whether APPA is really a “green” alternative for a minivan or not. To shed sufficient light on this question, the focus was placed on greenhouse gas emissions (CO2 and methane) of a Sky Bison compared to the CO2 and CH4 emissions of a minivan. [2]
The first question that comes to mind is, how can you compare a Sky Bison to a minivan when there is little to no data on the former? It is certainly no surprise that there are no studies on methane emissions of a Sky Bison. So a lot of assumptions have to be made to elaborate on this topic. And even then, the lack of essential information leaves a lot of room for debate.
The first assumption the author makes is that a Sky Bison is simply a large bison. Fortunately, for a bison, there is some data available. Bisons as we know them, weigh between 300 and 900 kg.[3] Sokka, on the other hand, described APPA as a 10-ton monster.[4] However, it is unclear whether this estimate is close to reality or not. For the sake of this article, let’s assume that this statement is true (except that APPA is a monster). This assumption would make APPA about a factor of 10 to 30 heavier than a normal bison.
Animals eat to meet their energy needs and depending on how much they eat, they also produce different amounts of methane. In order to estimate how much methane is emitted by a Sky Bison, it is necessary to estimate how much energy it needs. This leads to the second logical assumption: The difference in energy requirement between a normal bison and a flying bison is comparable to the difference between a mouse and a bat (which is essentially a flying mouse) and can thus be approximated. A normal mouse has a daily energy intake of 53.3 kJ ME/BW kg0.75/day[5] whereas a bat needs about 198.7 kJ ME/BW kg0.75/day (ME= Energy requirement, BW= Bodyweight).[6] From this data, one can logically conclude that a bat needs about four times more energy per day than a mouse. A bison, on the other hand, has an energy intake of 350 kJ ME/BW kg0.75/day.[7] This multiplicated by four means, that a Sky Bison has an energy intake of 1400 kJ ME/BW kg0.75/day. Since the Sky Bison weighs 10.000 kg, the daily energy requirement would be 5 161 700 kJ/ day. Tall grass prairie hay has a digestible energy of 1.56 to 2.32 Mcal/kg from which you can calculate the mass of hay APPA would need to eat, which is 791.16 kg to 532.42 kg per day.[8] With a 9 % methane yield (measured for a normal bison), this corresponds to 1309 kg of CH4 per Sky Bison per year.[9] The CO2 excretion is also closely related to the energy metabolism. Unfortunately, for lack of space, the calculation of the CO2 produced cannot be given. However, the amount was grossly estimated at 684 kg/year using data measured for ruminants.[10]
In this section, the author will now focus on the greenhouse gas emissions of a minivan. In contrast to the Sky Bison, there is plenty of data that can be used. The average CO2 emitted by minivans stands at 99 g/km in 2023.[11] Statistically, the majority of drivers in Germany travel between 5 000 and 10 000 km by car every year. Of course, this can vary from region to region, but for our calculations here we refer to these data.[12] This results in an annual CO2 emission of 495 to 990 kg. It turns out, that it is more difficult to estimate the methane emissions of a minivan than the CO2 emissions. CH4 emissions from vehicles are about 0.3 to 0.4 % of the amount of CO2 emitted. With this ratio, annual methane emission of 74 kg and 149 kg were estimated.[13]
While the sky bison’s CO2 emissions are still within the range of a minivan, its methane emissions exceed those of a minivan by far (9 to 18 times). However, it must be remembered that the calculation of methane emissions has been subject to major mental gymnastics and the figure may therefore be either grossly over- or underestimated. Looking at these numbers alone, it is clear that the Sky Bison is unfortunately not a greener alternative to a minivan. But to make a clearer decision, much more data needs to be generated and many more factors need to be taken into account to really decide which is more climate-friendly. For example, there are already results that immunizing sheep against ruman methanogens can reduce methane emissions. Perhaps this would also find an application in Sky Bisons.[14]
This article ignored many things like the infrastructure associated with Sky Bisons or whether a Sky Bison would theoretically need to be classified as a weapon since APPA was able to pick up and knock over two tanks in the Fire Nation battle. This would definitely add to a regulatory nightmare while making it more difficult to establish Sky Bisons in normal transport. In addition, no mention was made of how much greenhouse gas emissions are produced in the production of minivans and the roads they require. Many more issues have been left out, so the author invites the reader to further discuss the topic with some friends (for example in the Stuzi). Here is some food for thought: could agricultural land be provided to feed Sky Bisons without plunging humanity into famine? What is the legal basis: What would be laws that would have to be introduced if the Sky Bison were to be marketed as an alternative for cars? If you parked your Sky Bison in a Kurzparkzone without a parking permit, but it hovered over the parking space, would you still get a ticket? Do you need insurance? Do you classify it as a vehicle, a pet or a friend? Is it realistic to use Sky Bisons in big cities where there is hardly any space? How much does the life support of a Sky Bison cost and who can afford it? Do you need a driver’s license?…
The author hopes that this article has given the reader something to think about. And now, to conclude everything, the author would just like to point out that, of course, APA was used as the method of citation.
[1] Positionen Wien Energie. (2022, 14. Februar). CO2-Ausstoß Verkehr weltweit\: https://positionen.wienenergie.at/grafiken/emissionen-transport/
[2] Greenhouse Gas Emissions: Challenges, Technologies and Solutions. (2018). Deutschland: Springer Nature Singapore.
[3] Licht, D. S. (2016). Bison weights from national parks in the northern Great Plains. Rangelands. https://doi.org/10.1016/j.rala.2016.02.003
[4] Avatar-Wiki | Fandom. (o. D.). https://avatar.fandom.com/de/wiki/Avatar-Wiki
[5] National Academies Press (US). (1995). Nutrient requirements – NCBI Bookshelf. https://www.ncbi.nlm.nih.gov/books/NBK231918/
[6] Thomas, D. W. (1984). Fruit Intake and Energy Budgets of Frugivorous Bats. Physiological Zoology, 57(4), 457–467. http://www.jstor.org/stable/30163347
[7] Fortin, D., Fryxell, J.M. and Pilote, R. (2002), The Temporal Scale of Foraging Decisions in Bison. Ecology, 83: 970-982. https://doi.org/10.1890/0012-9658(2002)083[0970:TTSOFD]2.0.CO;2
[8] Olson, K. C. et al. (2008). Prediction of the energy content of Tallgrass Prairie HAY1. Journal of Animal Science. https://doi.org/10.2527/jas.2007-0564
[9] Crutzen, P. J., Aselmann, I. & Seiler, W. (1986). Methane production by domestic animals, wild ruminants, other herbivorous fauna, and humans. Tellus B, 38(3–4), 271. https://doi.org/10.3402/tellusb.v38i3-4.15135
[10] Madsen, J. S., Bjerg, B., Hvelplund, T., Weisbjerg \& Lund, P. (2010). Methane and carbon dioxide ratio in excreted air for quantification of the methane production from ruminants. Livestock Science, 129(1–3), 223–227. https://doi.org/10.1016/j.livsci.2010.01.001
[11] Minivans – Worldwide. Retrieved October 20, 2023, from https://de.statista.com/statistik/studie/id/50001/dokument/minivans-report/
[12] TÜV-Verband. (3. April, 2020). Wie viele Kilometer fahren Sie pro Jahr mit dem Auto? [Graph]. In Statista. Zugriff am 20. Oktober 2023, von https://de.statista.com/statistik/daten/studie/183003/umfrage/pkw-gefahrene-kilometer-pro-jahr/
[13] Nam, E. K.et al.(2004). Methane emissions from vehicles. Environmental Science \& Technology, 38(7), 2005–2010. https://doi.org/10.1021/es034837g
[14] Wright, A. D. G. et al. (2004). Reducing methane emissions in sheep by immunization against rumen methanogens. Vaccine, 22(29–30), 3976–3985. https://doi.org/10.1016/j.vaccine.2004.03.053
