The 36" International Conference of the System Dynamics Society, 2018
Meat or not? - A model-based analysis of the global diet change
dynamics
Sibel Eker Gerhard Reese Michael Obersteiner
International Institute for Applied University of Koblenz-Landau, International Institute for Applied
Systems Analysis (IIASA), Fortstrafe 7, 76829 Landau, Germany Systems Analysis (IIASA),
Schlossplatz 1, A-2361 Laxenbury, reese@ uni-landau.de Schlossplatz 1, A-2361 Laxenburg,
Austria Austria
eker@ iiasa.ac.at
Keywords: Human behavior, meat consumption, climate change, integrated assessment models
Extended Abstract
This study extends an existing integrated assessment model, namely the Felix Model (Rydzak et al.,
2013; Walsh et al., 2017), to capture the social and behavioral mechanisms behind diet change. This
extension is based on global diffusion of vegetarianism in response to climate events and social norms.
As illustrated in Figure 1, the threat of extreme weather events affects the attitude towards diet change.
This attitude change, however, forms a negative feedback loop of Willingness to change as the behavior,
i.e. lower meat consumption, lessens the climate change impacts, hence the perceived threat. The social
diffusion of behavior forms the positive feedback loop of Social transmission, as the higher number of
vegetarians shift the social norm (a term associated with the percentage of a behavior in population)
towards low meat consumption, which further stimulates the diet change behavior. The model also
accounts for the increasing meat consumption in developing countries as the income levels rise,
indicated by the Gross World Product. Furthermore, the model includes the effects of population
heterogeneity in terms of age, gender and education level on social transmission behavior, self-efficacy
and climate risk perception, respectively.
The model is quantified according to (i) the estimate of vegetarian population as 1.5 billion (21.5 in
2010 (Leahy, Lyons, and Tol, 2010); (ii) a reference behavior with an increasing vegetarian population
due to the increasing awareness in the western world, and (iii) empirical studies that show the relative
values of the psychological parameters (e.g. self-efficacy of women and men). Figure 2 shows the
reference simulation results and the uncertainty ranges resulting from a multivariate sensitivity analysis
with 500 simulations and +50% parameter ranges. In the reference simulation, the vegetarian population
increases until 2100, yet not at a rate sufficient to mitigate the adverse environmental impacts of
agriculture. Still, due to the lack of data on global diet change dynamics and various other uncertainties,
this model is used rather as a heuristic to explore various scenarios. In particular, a statistical screening
method (Ford and Flynn, 2005) is employed to identify the uncertainties that are most influential on
diet change dynamics. The findings show that the factors that relate the climate events to the attitude of
people towards diet change, for instance the number of events that trigger change (x0 risk attitude) or
time to forget the past events, are most influential on the long-term dynamics of the vegetarian
population.
The 36" International Conference of the System Dynamics Society, 2018
‘Average consumption
“= of animal calories per
+ capita
PA x
Food + +\
demand é
‘Animal calories in ‘Animal calories in
meat-based diet vegetarian diet
use
emissions
Gross World
\ Product
Meat-based wagmases
temperature Diet Followers Shift from 8
to
\— meat-eating
+ = NY
N Total
Occurence of sa population
rom
climate events change Responseettcacy cnt trom 7
mulielee vegetarianism ,
7 + Descriptive
Gender > Selfeficacy + social norm
—_ multiplier _
Perception of ‘e Social transmission
climate events Fraction intended to
+ change diet
Forgetting climate || perceived risk Se + +
events
2. Attitude multiplier Subjective norm
* for diet change multiplier
Education Age
Figure 1: An overview of the model structure of the diet change mechanism
1 Diet change dynamics over time
— Total Vegetarians
8 —— Total Meat Eaters
Population (billion people)
° 2020 2040 2080 2100
2060
Time (years)
Figure 2: Dynamics of Meat-hased Diet Followers and V egetarians in the reference simulation
The 36" International Conference of the System Dynamics Society, 2018
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