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MEDEAS-World: a new IAM framework integrating biophysical and socioeconomic constraints
Iñigo Capellán-Pérez1*, Ignacio de Blas1, Jaime Nieto1, Carlos De Castro1, Luis Javier Miguel1,
Margarita Mediavilla1, Óscar Carpintero1, Luis Fernando Lobejón1, Noelia Ferreras-Alonso2, Paula
Rodrigo1, Fernando Frechoso1, David Álvarez Antelo1, Pedro L. Lomas1, Gonzalo Parrado Hernando1.
1Group of Energy, Economy and System Dynamics of the University of Valladolid (Spain)
2CARTIF Foundation, Parque Tecnológico de Boecillo, Boecillo 47151, Spain
*Corresponding author: email@example.com.
Here MEDEAS-World is introduced, a new global energy-economy-environment model which is
being specifically developed to include feedbacks between subsystems and plausible alternative
assumptions which are not usually considered in IAMs. Particularly, MEDEAS-W considers: (1) input-
output economic analysis within a system dynamics structure; (2) geological supply constraints
determine non-renewable energies availability; (3) the techno-sustainable potential or renewables;
(4) potential mineral scarcity; (5) the energy return on energy invested (EROI) of the full energy
system and its feedback; and (6) climate change impacts consistent with natural scientists’
assessments. Experimental results confirm that current trends are deeply unsustainable, while a
simulation implementing Green Growth policies indicates that this paradigm may have serious
drawbacks which are not detected in models characterized by a sequential structure and considering
standard assumptions in relation to the aforementioned points.
Introduction & Methodology
Dozens, if not hundreds, Integrated Assessment Models (IAMs) have been developed in the last
decades since the pioneer World3 was developed in the early 1970s (Meadows et al., 1972). Despite
great advances performed in the field over the years, most IAMs (and especially those more policy-
influential), share a core set of common assumptions whose validity is being disputed in the
scientific discussion. First, IAMs are generally characterized by a rather sequential structure with
limited feedbacks among the represented subsystems. The discrepancy between natural scientists’
understanding of ecological feedbacks and the representations of environmental damage (if any)
found in IAMs is especially relevant for the case of climate change impacts, critically affecting policy-
advice (Cumming et al., 2005; Diaz and Moore, 2017; Lenton and Ciscar, 2013; Stern, 2013). Second,
a lack of plurality in the methods to represent the economic dimension has been detected in the
literature, dominated by conventional economic equilibrium and optimization approaches, with
important limitations to capture socioeconomic system dynamics and the role of macroeconomic
policies for sustainability governance (Hardt and O’Neill, 2017; Scrieciu et al., 2013). Third, fossil fuel
resource abundance, understood as the vast geological availability accessible at an affordable price,
is a default assumption in most of the prominent integrated assessment models (IAMs) used for
climate policy analysis; hence, future energy transitions are thus largely modelled as demand-driven
transformations (Capellán-Pérez et al., 2016; Höök and Tang, 2013). Fourth, it is usually assumed
that the resource base of renewable energy sources (RES) provides no practical limitation if
adequate investments are forthcoming, which is disputed by a branch of literature (de Castro et al.,
2014, 2013, 2011; Miller and Kleidon, 2016; Moriarty and Honnery, 2016). Finally, fifth, most models
adopt a gross energy approach disregarding the implications that the future evolution of the Energy
Return on Energy Investment (EROI) may have for the system (Carbajales-Dale et al., 2014).
Here we present the global version of the MEDEAS framework (EU and country-level models are in-
development), which is been designed with the aim to tackle the aforementioned limitations in the
current state-of-the art of IAMs. MEDEAS-World (MEDEAS-W) is a global, one-region, simulation
model which has been designed applying System Dynamics,1 which facilitates the integration of
knowledge from different perspectives and disciplines as well as the feedbacks from different
subsystems. The model typically runs from 1995 to 2050 (although the simulation horizon may be
extended to 2100 if necessary, e.g. when focusing on climate change issues). MEDEAS-W is
structured into seven main submodules: Economy, Energy, Infrastructures, Materials, Land Use,
Social and Environmental Impacts Indicators and Climate Change (see Figure 1). The main variables
that connect the different modules are represented by arrows.
Figure 1: MEDEAS-World model schematic overview. Source: (Capellán-Pérez et al., 2017).
The main characteristics of each module are:
• Economy and population: the global economy in MEDEAS is modelled following a post-
Keynesian approach assuming non-clearing markets (i.e. not forcing general equilibrium) and
demand-led growth, combined with supply-side constraints such as energy availability. The
economic structure is captured by the adaptation and dynamic integration of global WIOD
1 Developed in Vensim DSS software for Windows Version 6.4E (x32). Also available in Python open-source
(NR & RES
CC damage function
Requi red mate rials
for energy systems
Mater ial consumption
Energy for material
input-output tables resulting in 35 industries and 4 institutional sectors (Dietzenbacher et
al., 2013). Final energy intensities by sector are obtained combining information from WIOD
environmental accounts (Genty, 2012) and the IEA Balances (2018). Population evolves
exogenously as defined by the user. See (Nieto et al., 2018) for more details on this
• Energy: this module includes the renewable and non-renewable energy resources potentials
and availability taking into account biophysical and temporal constraints. In particular, the
availability of non-renewable energy resources depends on both stock and flow constraints
(Campbell and Laherrère, 1998; Kerschner and Capellán-Pérez, 2017; Mohr et al., 2015).
Comprehensive analysis of the techno-sustainable potential of RES for electricity and heat
(de Castro et al., 2014, 2013, 2011; Moriarty and Honnery, 2016). In total, 34 primary energy
sources and 5 final fuels are considered (electricity, heat, solids, gases and liquids), with
large technological disaggregation. The intermittency of RES is considered in the framework,
computing endogenous levels of overcapacities, storage and overgrids depending on the
penetration of variables RES technologies. A net energy approach accounting for the Energy
return on energy invested (EROI) of individual technologies as well as for the whole system is
applied (which is in turn feed-backed to the Economy module). Transportation is modelled in
high detail, differentiating between different types of vehicles for households, as well as
freight and passenger inland transport).
• Energy infrastructures represent power plants to generate electricity and heat.
• Climate: this module projects the climate change levels due to the greenhouse gas emissions
generated by human societies (non-CO2 emissions are exogenously set taking as reference
the Representative Concentration Pathways scenarios (van Vuuren et al., 2011)). The carbon
and climate cycle is adapted from C-ROADS (Fiddaman et al., 2016; Sterman et al., 2012).
This module includes a climate damage function consistent with natural scientists’
assessments which dynamically affects sectors’ economic output depending on the level of
global temperature change.
• Materials: materials are required by the economy with emphasis on those required for the
construction and O&M of alternative energy technologies (De Castro et al., 2018). Option of
recycling policies available. Estimation of the potential mineral scarcity,
• Land-use: this module currently mainly accounts for the land requirements of the RES
• Social and environmental impacts: this module translates the “biophysical” results of the
simulations into metrics related with social and environmental impacts. The objective of this
module is to contextualize the implications for human societies in terms of well-being for
(For a detailed documentation of the MEDEAS-World model, see (Capellán-Pérez et al., 2017)).
Despite MEDEAS-W is still in development, it is already possible to produce experimental results.
Two scenarios are simulated in MEDEAS global model to 2050 in order to illustrate the importance of
considering all the aforementioned factors in the planning of the transition towards a low carbon
economy: (1) Business-as-usual (BAU, continuation of current trends) and (2) “Green Growth” (GG,
higher economic growth, faster transition to RES, higher efficiency improvements, etc.).
BAU scenario outputs indicate that, if current trends continue, economic growth will not be able to
be maintained globally in the next decades due to the interaction of dangerous climate change and
energy scarcities. The policy targets applied in the GG scenario allow for a lower temperature
increase by the mid-century (+1.7ªC); however, this is at the cost of a fall in the EROI of the energy
system (<4:1): the fast transition to RES in the GG scenario implies a re-materialization of the
economy. Moreover, the economic demand driven by the levels of desired GDPpc cannot be
satisfied over the studied period due to the inability of RES, efficiency improvements and alternative
technologies to reach a substitution rate to compensate the decline in fossil fuel availability. As a
result, the GDPpc is in a downward trend by the end of the studied period also in this scenario. The
obtained results indicate that the GG paradigm, often promoted by institutions as the way to going
forward to achieve a sustainable energy transition, may have serious drawbacks when considering
feedbacks and plausible alternative assumptions which are not considered in most models of the
As any model, MEDEAS-W is subject to a number of limitations which are planned to be addressed in
future work. Among them, we highlight the following: full dynamization of the IO matrixes and
allocation of energy scarcities, consideration of inequalities within and between countries, the
extension of the net energy approach to all energy technologies and resources and the inclusion of a
full land-use submodule.
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