TEDx Boulder 2017 - Transcript, references, credits

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I gave a talk at TEDx Boulder on Sept 17, 2017. Below is a transcript of my talk, a list of the references that support it, and credits for the images used in my slides. I'm very grateful to Austin Virts for his help with the slides.

Leaving a smaller carbon foodprint

We buy locally produced food for many reasons. Local food can be fresher, tastier, and healthier. Buying directly from a producer can develop trust between farmer and consumers. Farmers markets and other local food outlets can help educate us, promote mindful eating, and build community. Sometimes we just want to know that the chicken we’re about to eat had enough space and plenty of friends.

And then, there are food miles. We’re all familiar with this idea: that locally produced food has to travel less far to reach us, and so we reduce greenhouse gas emissions from fossil fuels used for transportation. Locally-produced food: smaller carbon footprint. Foodprint, if you will. It is an attractive logic, and I frequently hear students in my food systems classes argue that in order to reduce our foodprint, we should choose to buy more food that is produced nearer to us.

But, the food miles concept is flawed [1, 2]. A closer examination of the data shows us that it’s extremely unlikely that buying food produced nearer to us will significantly reduce emissions. Here’s why.

First, the proportion of food-related emissions that come from transportation is tiny. Greenhouse gases are produced at every stage of a food’s life-cycle: from transportation, yes; but also from the inputs of seed, fertilizer, pesticides; from on-farm production practices such as clearing land, plowing, irrigating, and harvesting; from processing and packaging; and from refrigeration, and storage. And, on average, in the US, moving the food from the producer to retailer only accounts for about 4% of these total cradle-to-grave food system emissions [3] – and this is the only section of the whole supply chain that is shortened by locally-produced food. In contrast, around 80% of emissions come from the on-farm production stage.

None-the-less, 4% of food emissions is a lot of carbon, when scaled up over a person’s lifetime or over a society: wouldn’t it be worth reducing this by buying local? Well, yes of course: if all else were equal. But the majority of the time, all else is not equal! If producing food locally means producing it in places where soil and climate are anything other than optimal, then production quickly becomes less efficient, and more emissions will be generated in compensating for that inefficiency than will be saved by reducing transportation.

A couple of examples: both from studies conducted in the UK.

Tomatoes are grown commercially in the UK. But for much of the year, this requires the use of heated greenhouses, because the climate isn’t sufficiently warm or sunny. England is not a sunny place – trust me, I grew up there. So, for a consumer buying tomatoes in the UK, the emissions from domestically-produced tomatoes can be up to four times higher than from sun-grown tomatoes from Spain [4].

A second example: producing lamb on pasture land in New Zealand, and shipping it all the way around the world to the UK, can generate far fewer greenhouse gas emissions than producing lamb in the UK that requires supplemental animal feed [5, 6].

These examples are more the rule than the exception. For most food products, a small number of regions will have optimal growing conditions, and will therefore have a comparative advantage in production efficiency. It’s possible to grow avocadoes in Colorado; it’s much more emissions-efficient to grow them in California and then transport them. These geographic comparative advantages help explain why the food miles concept does not stand up to scrutiny.

A second factor here is that how far food is moved matters much less than by what mode of transport it is moved. Commercial food transport is often by relatively high-efficiency vehicles: thousands of units of food can be moved by a single ship or truck; consequently, the emissions per unit food can be very small. In contrast, our personal vehicles are incredibly inefficient: if thousands of us drive even a mile or two to pick up a small amount of food, the emissions per unit food that we generate may be much higher. Maybe grocery store and CSA delivery services have something to offer in this regard [7].

This is not an attack on local food. There is undoubtedly enormous value in developing relationships with the amazing farmers that produce our food, and in knowing that Colin the chicken lived a good life. Let’s continue buying some of our food locally, for those and other reasons. But let’s not fool ourselves that simply reducing the distance that food travels between producer and retailer is an effective way of doing our bit to mitigate climate change.

But then: if we want to fight climate change; if we think that individual behavioral changes are part of the solution; and if we want to reduce emissions from our food choices in particular… are there choices we can make that would help?

Absolutely! The data consistently show that dramatically reducing or eliminating our consumption of animal products would vastly reduce emissions from the food system [8, 9].

Compared side-by-side, all animal proteins generate higher emissions per kg of product than do plant proteins [10-12]. But not all animal products are equal. Or, as on George Orwell’s farm, some animal products are more equal than others. Specifically: from an emissions perspective, cow and sheep products are dramatically worse than other animal products [11].

That’s because cattle and sheep are ruminants – their digestive systems generate enormous amounts of methane through a process called enteric fermentation. Put simply, cow burps are really bad for the climate.

Perhaps surprisingly, the data from this – and other meta-analyses of multiple independent studies – suggest that the production of extensively-raised grassfed beef can generate higher emissions than intensively-raised feedlot beef [10-12]. That’s for at least two reasons. First, grassfed cows are likely to take longer to reach slaughter weight: and so they are alive for longer and belch out more methane [13]. And second, grass fed systems require much more space. In many parts of the world, this means clearing natural vegetation to create pasture land. Indeed, in the Brazilian Amazon, where I conduct most of my research, the creation of cattle pasture is the leading cause of deforestation [14]. Cutting down forests releases vast quantities of carbon dioxide [15]. It also removes critical habitats that other species need to survive.

So: you may not be concerned about climate change. Or you may be concerned, but think that food decisions are not the way you want to address your personal carbon footprint. And there may be some rationale in that: a recent study suggested that the individual behaviors that will have the largest impacts on climate change mitigation are having one less child, flying less, and choosing greener personal vehicles [16]. But eating a plant-based diet is next on that list. And there’s a critical distinction between some of these behaviors: we will each, at most, only ever make a handful of decisions about how many children to have, and decisions about what car to drive maybe every decade or so. In contrast, we make food choices every single day. Eating a more plant-based diet, or at very least a diet that dramatically cuts back on cow and sheep products – including both meat and dairy – is probably the single biggest immediate action most of us can take to reduce greenhouse gas emissions. We each have the opportunity to walk out of here tonight and choose to reduce our carbon foodprint. Thank you.


1.         Shimizu, H. and P. Desrochers, Yes We Have No Bananas: A Critique of the'Food Miles' Perspective, in Mercatus Policy Series No. 8. 2008. Available at: http://dx.doi.org/10.2139/ssrn.1315986

2.         Coley, D., M. Howard, and M. Winter, Food miles: time for a re‐think? British Food Journal, 2011. 113(7): p. 919-934.

3.         Weber, C.L. and H.S. Matthews, Food-miles and the relative climate impacts of food choices in the United States. Environmental Science & Technology, 2008. 42(10): p. 3508-3513.

4.         Watkiss, P., et al., The validity of food miles as an indicator of sustainable development. Final report prepared by AEA Technology Environment for DEFRA, London, 2005.

5.         Ledgard, S.F., et al., Carbon footprinting of New Zealand lamb from the perspective of an exporting nation. Animal Frontiers, 2011. 1(1): p. 40-45.

6.         Saunders, C. and A. Barber, Carbon footprints, life cycle analysis, food miles: global trade trends and market issues. Political Science, 2008. 60(1): p. 73-88.

7.         Coley, D., M. Howard, and M. Winter, Local food, food miles and carbon emissions: A comparison of farm shop and mass distribution approaches. Food Policy, 2009. 34(2): p. 150-155.

8.         Smith, P., et al., Agriculture, forestry and other land use (AFOLU), in Climate Change 2014: Mitigation of Climate Change. Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change O. Edenhofer and et al, Editors. 2014, Cambridge University Press: Cambridge, UK and New York, NY, USA.

9.         Aleksandrowicz, L., et al., The impacts of dietary change on greenhouse gas emissions, land use, water use, and health: a systematic review. PLOS ONE, 2016. 11(11): p. e0165797.

10.       Nijdam, D., T. Rood, and H. Westhoek, The price of protein: Review of land use and carbon footprints from life cycle assessments of animal food products and their substitutes. Food Policy, 2012. 37(6): p. 760-770.

11.       Ripple, W.J., et al., Ruminants, climate change and climate policy. Nature Climate Change, 2014. 4(1): p. 2-5.

12.       Swain, M., et al., Reducing the environmental impact of global diets. Science of the Total Environment, 2018. 610-611: p. 1207-1209.

13.       Pelletier, N., R. Pirog, and R. Rasmussen, Comparative life cycle environmental impacts of three beef production strategies in the Upper Midwestern United States. Agricultural Systems, 2010. 103(6): p. 380-389.

14.       Bowman, M.S., Impact of foot-and-mouth disease status on deforestation in Brazilian Amazon and cerrado municipalities between 2000 and 2010. Journal of Environmental Economics and Management, 2016. 75: p. 25-40.

15.       Cederberg, C., et al., Including carbon emissions from deforestation in the carbon footprint of Brazilian beef. Environmental Science & Technology, 2011. 45(5): p. 1773-1779.

16.       Wynes, S. and K.A. Nicholas, The climate mitigation gap: education and government recommendations miss the most effective individual actions. Environmental Research Letters, 2017. 12(7).

Image credits

Slide 1, Local food - Credit: Walmart. Available here, under a creative commons license.

Slide 3, Food miles - Original image by Austin Virts

Slide 4, Food chain - Original image by Austin Virts

Slide 5, Tomatoes - Available here, under a creative commons license.

Slide 6, London - Credit: George Tsiagalakis. Available here, under a creative commons license.

Slide 7, Lamb - Available here, under a creative commons license.

Slide 8, Cars - Available here, under a creative commons license.

Slides 9 & 11, Graphs - Figures recreated by Peter Newton. Data from reference [12] above.

Slide 10, Cow - Credit: John Haslam. Available here, under a creative commons license.

Slide 12, Cattle & deforestation - Credit: Alex Lees. Permission granted.