The other Tilman paper we ought to know about

By Joern Fischer

Just a few days ago, I posted something on how different kinds of framing change what you believe ought to be done in a given setting. I’ve just stumbled into a nice example of this, and I thought I’d share this with the readers of this blog. Do we need to double agricultural production by 2050 or not?

Citing Tilman (2002, Nature), many papers start by stating the “need” to double production by 2050. Alternatively, authors could cite Tilman & Clark (2014, Nature) – who state that if we changed our diets to less or no meat consumption, we would have a much lower environmental impact. And we’d need less land for agriculture.

Which shall we assume? That demand will inevitably double, by a larger, more carnivorous human population? Or that demand will less than double, because diets can be altered? Our policy advice will differ, depending on which world we assume: we will either recommend producing more, or eating less meat.

So next time you cite one of the many great Tilman papers — check your assumptions, and perhaps cite the other one!


One thought on “The other Tilman paper we ought to know about

  1. Hi Joern —

    I’ve been meaning to start writing a peer-reviewed piece on this, but am predictably swamped — but have you read Doug Boucher’s analysis of the predicted food “needs”, or Tim Wise’s? Doug’s: ; Tim’s:

    I had read Tim’s before, but it was Doug’s the made it clear to me: from what I can tell, for all practical intents and purposes, the 60% to doubling production number is complete bunk. It is, as Doug points out, measured in $ of food. It wasn’t until Doug put it this way that I understood Tim’s point, that these were “projections” not “predictions” of need. The difference escaped me, but the 60% increase is a projection based on the estimated size of the food market in dollars, which is not a terribly sensible way to estimate how much food we will “need” in the future.

    I thought Tilman et al. had used Alexandratos’s estimation, but they point out in their 2011 piece that their methods are based on income-dependent calorie and kg protein models. Interesting. I had not realized that there was an independent source of the “doubling” number, which Alexandratos’s team corrected to 60% in any case.

    I’m glad their newer piece includes considerations of diet and waste change. It also, however, still assumes “continued market failure” in that I’ve recently come across further estimates of food system externalities (in addition to Pretty: ( and Tegtmeier and Duffy ( : and Needless to say, it seems likely that continued non-incorporation of externalities that are themselves larger than the profits generated would continue us on an unsustainable path to 2050.

    The whole thing is somewhat bemusing, actually, as neither Tilman et al nor Alexandratos are truly estimates of how much we will “need”. Many argue that defining how much we need assuming even distribution, lower waste, and nutritional adequacy is unrealistic because all these trends will continue and we need to deal with “reality”. But of course as I often say, an divergence from the unsustainable status quo by definition will break from “realistic” extrapolations that “bake in” current patterns–whether you’re talking about GHGs or poverty reduction.

    The whole conversation gets very vexed and confusing here. Somehow “most parsimonious extrapolation” becomes “need”. I’m very glad Tilman et al. have mapped out several scenarios now, which is a better framing, and include many of the critiques.

    So perhaps we should start talking about the “need” to change diets, change food distribution, empower women, and reduce waste. While those have increasingly made it into the conversation, there is not really (to me) a defensible reason to speak of the “need” for more production rather than the “need” for these other changes.

    Nothing new to you of course, and basically says “Yes, you’re right Joern, that’s a good recommendation” 😉

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