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What are the carbon opportunity costs of our food?

We get this figure from the change in actual versus potential carbon stocks from current agricultural land. This amounts to 387 gigatonnes of

  • We get this figure from the change in actual versus potential carbon stocks from current agricultural land. This amounts to 387 gigatonnes of carbon, which is equal to 1417 gigatonnes of CO2.

    Erb, K. H., Kastner, T., Plutzar, C., Bais, A. L. S., Carvalhais, N., Fetzel, T., … & Luyssaert, S. (2018). Unexpectedly large impact of forest management and grazing on global vegetation biomass. Nature, 553(7686), 73-76.

  • Each year we emit around 36 billion tonnes of CO2 from fossil fuels. So we calculate this as [1417 / 36 = 40 years].
  • Schmidinger, K., & Stehfest, E. (2012). Including CO2 implications of land occupation in LCAs—method and example for livestock products. The International Journal of Life Cycle Assessment, 17(8), 962-972.
  • All of the dietary scenarios have been designed to meet nutritional requirements.
  • One of the challenges of quantifying these carbon opportunity costs on an annual per capita basis is that it is highly dependent on a couple of factors: the uptake rate of different diets by individuals, and the period over which these carbon savings in vegetation would accumulate. When a forest or grassland is returning, carbon storage takes years (in fact, decades) to accumulate until eventually this additional sequestration saturates. In other words, this additional carbon saving will not continue indefinitely. Later in the article we look at the total maximum carbon sequestration approach which accounts for this time dependence. Nonetheless, in this study by Joseph Poore and Thomas Nemecek (2018), based on the work of Kurt Schmidinger & Elke Stehfest (2012) is based on the savings over a 100-year period.

    Poore, J., & Nemecek, T. (2018). Reducing food’s environmental impacts through producers and consumers. Science, 360(6392), 987-992.

  • Hayek, M. N., Harwatt, H., Ripple, W. J., & Mueller, N. D. (2020). The carbon opportunity cost of animal-sourced food production on land. Nature Sustainability, 1-4.
  • To quantify the opportunity costs, they took the amount of carbon stored in vegetation and soils in existing pastures (used for livestock grazing) and croplands used to grow animal feed today, versus the amount that could be stored if we abandoned this land and let it naturally regenerate (accounting for the changes in cropland that would be required to replace meat and dairy products with plant-based alternatives). Obviously land potential across the world is very different: pasture tends to store more carbon than cropland; wild grasslands store more than managed pastures; tropical forests store more than temperate forests. They aimed to take all of this into account by quantifying these differences at a high spatial resolution.

    West, P. C., Gibbs, H. K., Monfreda, C., Wagner, J., Barford, C. C., Carpenter, S. R., & Foley, J. A. (2010). Trading carbon for food: Global comparison of carbon stocks vs. crop yields on agricultural land. Proceedings of the National Academy of Sciences, 107(46), 19645-19648.

  • Alexandratos, N. & Bruinsma, J. World agriculture towards 2030/2050: the 2012 revision. FAO 20, 375 (2012).
  • This we calculate as [547 / 36 = 15.2 years].

    Obviously this scenario would only be desirable if we could still produce enough food for everyone to have a nutritious diet. This scenario takes this into account, and after accounting for consumer waste, provides an average of 2845 kilocalories and 76 grams of protein per person per day. This would be more than the global average requirements.

    The WHO recommends a minimum protein intake of 0.8 grams per day per kilogram of bodyweight. For a person that weighs 60 kilograms, this would equate to 48 grams of protein per day; for a 70kg person this would be 56 grams; and for a 90 kilogram person this would be 72 grams of protein. Averaged over a population, 76 grams of protein would be sufficient for everyone to meet this requirement.

    World Health Organization, & United Nations University. (2007). Protein and amino acid requirements in human nutrition (Vol. 935). World Health Organization.

  • This would give us a total of 775 billion tonnes of CO2 by 2100 – very close to the estimate of 810 billion tonnes we’d get by multiplying the 8.1 GtCO2e carbon sequestration figure from the previous section by 100 years.
  • The EAT-Lancet diet was designed by a group of researchers in nutrition, health, sustainability and policy to balance and improve both human and environmental health.

    Willett, W., Rockström, J., Loken, B., Springmann, M., Lang, T., Vermeulen, S., … & Murray, C. J. (2019). Food in the Anthropocene: the EAT–Lancet Commission on healthy diets from sustainable food systems. The Lancet, 393(10170), 447-492.

  • We emit around 36 billion tonnes of CO2 each year from fossil fuels. So we can calculate this as [332 / 36 = 9.2 years].
  • Since climate models come with a certain degree of uncertainty – there is a range within which we can predict how the climate will respond – we tend to give probability values to each of these budgets. For example, as of 2020, to have a 50% change of keeping global average temperature rise below 1.5℃, we can emit 440 billion tonnes of CO2. To have a 67% chance, we can emit only 227 billion tonnes; and for a 33% chance, this increases to 673 billion tonnes CO2. That’s around 12 years of fossil fuel emissions, if they stay at their current levels.

    Matthews, H. D., Tokarska, K. B., Rogelj, J., Smith, C. J., MacDougall, A. H., Haustein, K., … & Knutti, R. (2021). An integrated approach to quantifying uncertainties in the remaining carbon budget. Communications Earth & Environment, 2(1), 1-11.

  • For each carbon budget we also show the remaining budget to have a 33% and 67% chance of keeping temperatures below this value. This is shown by the confidence intervals for each.

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