Is Global Collapse Imminent? An Updated Comparison of The
Limits to Growth with Historical Data
Research Paper No. 4 August 2014
About MSSI Research Papers
MSSI’s Research Papers Series is a key communication initiative of the Melbourne Sustainable Society Insti-
tute, aimed at stimulating thought and discussion within the University of Melbourne and broader commu-
nity and showcasing the scholarship of MSSI.
Dr Lauren Rickards, Melbourne Sustainable Society Institute, Lauren.Rickards@unimelb.edu.au
Dr Graham M. Turner is a Principal Research Fellow at the Melbourne Sustainable Society Institute, Univer-
sity of Melbourne, Australia.
This Paper draws substantially on the following publication, with additional material incorporated: Turner
G 2012, On the cusp of global collapse? Updated comparison of the Limits to Growth with historical data.
GAiA, 21, pp. 116-124.
Citing this report
Please cite this paper as Turner, G. (2014) ‘Is Global Collapse Imminent?’, MSSI Research Paper No. 4,
Melbourne Sustainable Society Institute, The University of Melbourne.
ISBN: 978 0 7340 4940 7
The Limits to Growth “standard run” (or business-as-usual, BAU) scenario produced about forty years
ago aligns well with historical data that has been updated in this paper. The BAU scenario results in
collapse of the global economy and environment (where standards of living fall at rates faster than
they have historically risen due to disruption of normal economic functions), subsequently forcing
population down. Although the modelled fall in population occurs after about 2030—with death
rates rising from 2020 onward, reversing contemporary trends—the general onset of collapse rst
appears at about 2015 when per capita industrial output begins a sharp decline. Given this imminent
timing, a further issue this paper raises is whether the current economic difculties of the global
nancial crisis are potentially related to mechanisms of breakdown in the Limits to Growth BAU
scenario. In particular, contemporary peak oil issues and analysis of net energy, or energy return
on (energy) invested, support the Limits to Growth modelling of resource constraints underlying the
Checking on the Limits to Growth
With over forty years of hindsight available since The Limits to Growth (LTG) was rst published
(Meadows et al., 1972, Meadows et al., 1974), it is timely to review how society is tracking relative
to their ground-breaking modelling of scenarios, and to consider whether the global economy and
population is on a path of sustainability or collapse. Over a similar timeframe, international efforts
based around a series of United Nations (UN) conferences have yielded mixed results at best (Lin-
ner and Selin, 2013, Meadowcroft, 2013). In addition to unresolved critical environmental issues and
resource constraints such as anthropogenic climate change and peak oil, the global economy is also
beset by ongoing challenges from the Global Financial Crisis (GFC), not least of which are lingering
levels of extraordinary debt. The standard political remedy of growing the economy out of debt has
potential ramications for environmental stability, with evident negative feedbacks on the economy.
The intertwined economy-environment dependencies embodied in the original 1970’s LTG model-
ling provide an opportunity to examine how the global predicament has unfolded and what it might
mean for the future.
Through a dozen scenarios simulated in a global model (World3) of the environment and economy,
Meadows et al. (1972, p. 125) identied that “overshoot and collapse” was avoidable only if consid-
erable change in social behaviour and technological progress was made early in advance of environ-
mental or resource issues. When this was not achieved in the simulated scenarios, collapse of the
economy and human population (ie. a relatively rapid fall) occurred in the 21st century, reducing
living conditions to levels akin to the early 20th century according to the modelled average global
conditions. Exactly how this would play out in the real world is open to conjecture, as noted below.
Despite the LTG initially becoming a best-selling publication, the work was subsequently largely
relegated to the “dustbin of history” by a variety of critics (eg., Lomborg and Rubin, 2002). These
critics perpetuated the public myth that the LTG had been wrong, saying that it had forecast col-
lapse to have occurred well before year 2000 when the LTG had not done this at all. Ugo Bardi’s
The Limits to Growth Revisited (2011) comprehensively details the various efforts to discredit the LTG
study. He draws parallels with documented campaigns against the science of climate change and
tobacco health impacts. Three economists- Peter Passel, Marc Roberts, and Leonard Ross- initiated
criticisms in a New York Times Sunday Book Review article in 1972. They made false statements (eg.
“all the simulations based on the Meadows world model invariably end in collapse”), and also incor-
rectly claimed that the book predicted depletion of many resources by about 1990. The US econo-
mist William Nordhaus made technically erroneous judgements (in 1992) by focusing on isolated
equations in World3 without considering the inuence that occurs through the feedbacks in the
rest of the model. In 1973 a critique of the LT G , edited by physicist Sam Cole and colleagues at the
University of Sussex, contained a technical review of the World3 modelling and essays based on
ideology that attacked the authors personally. According to Bardi, the technical review fails because
it largely concerned how the World3 model could not be validated from the perspective of simple
linear modelling, which is an inappropriate test for a non-linear model. The review also established
that the model could not run backwards in time, though this is an unnecessary requirement for the
model to run forward properly. Criticism of the study continued for about two decades, including
other noted economists such as Julian Simon, along the vein of such misunderstandings and per-
sonal attacks. For the last decade of the twentieth century, however, criticism of the LTG centred on
the myth that the 1972 work had predicted resource depletion and global collapse by the end of
that century. Bardi identies a 1989 article titled “Dr. Doom” by Ronald Bailey in Forbes magazine
as the beginning of this view. Since then it has been promulgated widely, including through popular
commentators such as the Danish statistical analyst Bjørn Lomborg, and even in educational texts,
peer-reviewed literature, and reports by environmental organisations.
Over the last decade, however, there has been something of a revival in awareness and understand-
ing of the LTG . Most recently, Randers (2012a)—a LTG co-author—has published his forecast of the
global situation in 2052 and renewed the lessons from the original publication (Randers 2012b).
A turning point in the debate occurred in 2000 with the energy analyst Simmons (2000) raising
the possibility that the LTG modelling was more accurate than generally perceived. Others have
made more comprehensive assessments of the model output (Hall and Day, 2009, Turner, 2008);
indeed, my earlier work found that thirty years of historical data compared very well with the LTG
“standard run” scenario. The standard run scenario embodies the business-as-usual (BAU) social
and economic practices of the historical period of the model calibration (1900 to 1970), with the
scenario modelled from 1970 onwards.
This paper presents an update on the prior data comparison by Turner (2008). An update is es-
pecially pertinent now because of questions raised about how the current economic downturn—
commonly associated with the GFC—may relate to the onset of collapse in the LTG BAU scenario.
Is it possible that aspects leading to the collapse in the LTG BAU scenario have contributed to the
GFC-related economic downturn? Could it be that this downturn is therefore a harbinger of global
collapse as modelled in the LTG ?
To provide context and convey the importance of understanding global dynamics, this paper rst
summarises the mechanisms that play-out in the modelled BAU scenario. Subsequently, the mod-
elled trajectory is compared with some forty-years of historical data (which are outlined in the ap-
pendix). The appendix also provides comparison of the data with two other scenarios, namely “com-
prehensive technology” and “stabilized world” scenarios (with full details in Turner, 2012)—showing
that the comparison strongly favours the BAU scenario only. On the basis of this comparison, we
discuss what the modelling might mean for a resource-constrained global economy. In particular, the
paper examines the issue of peak oil and the link between energy return on investment (EROI) and
the LTG World3 model. The ndings lead to a discussion of the role of oil constraints in the GFC,
and a consideration of the link between these constraints and general collapse depicted in the LTG.
This paper does not attempt to deal with the critical but vexed issue of appropriate governance;
other research is shedding light on the difculties thwarting change (eg. Harich, 2010, Rickards et
al., 2014). Instead, it aims to forewarn of potential global collapse—perhaps more imminent than
generally recognised—in the hope that this may spur on change, or at least to prepare readers for a
worst case outcome.
Modelling future worlds
The computer model called World3, developed for the LTG study, simulated numerous interactions
within and among the key subsystems of the global economy: population, industrial capital, pollution,
agricultural systems, and non-renewable resources. For its time, World3 was necessarily coarse, for
example modelling the total global population rather than separate regions or nations. In the system
dynamics approach, causal links were made mathematically to reect the inuence of one variable
on another (not necessarily in a linear fashion), both within and between various sectors of the
global economic system. In this way, positive and negative feedback loops were established, where
the outcome in one part of the system subsequently returns by a chain of inuences to affect itself.
When positive and negative feedback loops are nely balanced, a steady state outcome results (or
oscillations about an average); however, when one loop dominates, an unstable state is the result,
such as the simple case of exponential growth when there is a dominant positive feedback. A classic
example is the accelerating growth of a biological population, such as bacteria, in which the birth
rate at one point in time is proportional to the size of the population at that time.
The effect and control of these feedbacks depends on the presence of delays in the signals from
one part of the world system to another. For instance, the effects of increasing pollution levels on
human life expectancy or agricultural production may not be recognised for some decades after
the pollution is emitted. This is important because unless the effects are anticipated and preventive
action taken in advance, the increasing levels of pollutants may grow to an extent that prohibits cor-
rection. These are the dynamics that lead to “overshoot and collapse”.
The World3 model simulated a stock of non-renewable as well as renewable resources. The func-
tion of renewable resources in World3, such as agricultural land and the trees, could erode as a
result of economic activity, but they could also recover their function if deliberate action was taken
or harmful activity reduced. The rate of recovery relative to rates of degradation affects when
thresholds or limits are exceeded as well as the magnitude of any potential collapse.
To explore “the broad behaviour modes of the population-capital system” (Meadows et al. 1972, 91)
the LTG presented a dozen scenarios exploring the effects of various technological improvements
and societal or policy changes. The scenario series started with a “standard run” which encapsu-
lated business-as-usual (BAU) values in the model for the future. Parameter trends for this scenario
were based on historical data and behaviour (established to reproduce approximately the growth
and dynamics observed from 1900 to 1970).
Impending collapse of the BAU scenario
As described below, data from the forty years or so since the LTG study was completed indicates
that the world is closely tracking the BAU scenario. In the BAU, during the 20th century increasing
population and demand for material wealth drives more industrial output, which grows at a faster
rate than population. Pollution from increasing economic activity increases, but from a very low
level, and does not seriously impact the population or environment.
However, the increased industrial activity requires ever increasing resource inputs (albeit offset by
improvements in efciency), and resource extraction requires capital (machinery) which is pro-
duced by the industrial sector (which also produces consumption goods). Until the non-renewable
resource base is reduced to about 50 per cent of the original or ultimate level, the World3 model
assumed only a small fraction (5 per cent) of capital is allocated to the resource sector, simulat-
ing access to easily obtained or high quality resources, as well as improvements in discovery and
extraction technology. However, as resources drop below the 50 per cent level in the early part of
the simulated 21st century and become harder to extract and process, the capital needed begins to
increase. For instance, at 30 per cent of the original resource base, the fraction of total capital that
is allocated in the model to the resource sector reaches 50 per cent, and continues to increase as
the resource base is further depleted (shown in Meadows et al., 1974).
With signicant capital subsequently going into resource extraction, there is insufcient capital
available to fully replace degrading capital within the industrial sector itself. Consequently, despite
heightened industrial activity attempting to satisfy multiple demands from all sectors and the
population, actual industrial output (per capita) begins to fall precipitously from about 2015, while
pollution from the industrial activity continues to grow. The reduction of inputs to agriculture from
industry, combined with pollution impacts on agricultural land, leads to a fall in agricultural yields
and food produced per capita. Similarly, services (eg. health and education) are not maintained due
to insufcient capital and inputs.
Diminishing per capita supply of services and food causes a rise in the death rate from about 2020
(and a somewhat lower rise in the birth rate, due to reduced birth control options). The global
population therefore falls, at about half a billion per decade, starting at about 2030. Following the
collapse, the output of the World3 model for the BAU (Figure 1) shows that average living stan-
dards for the aggregate population (material wealth, food and services per capita basically reecting
OECD-type conditions) resemble those of the early 20th century.
The implications of the BAU scenario are stark: Figure 1 depicts global collapse of the economic
system and population. Essentially this collapse is caused by resource constraints (Meadows et al.,
1972), following the dynamics and interactions described above. The calibrated dynamics reect
observed responses within the economy to changing levels of abundance or scarcity (Meadows et
al., 1974), obviating the need for modelling prices as the communication channel of the economic
The LTG ‘Business As Usual’ scenario tracks reality
With forty years passing since the original LTG modelling, it is opportune to examine how well the
scenarios reect reality. In this section a graphical comparison is presented of the historical data
with the BAU scenario described above (Figure 1). It is evident from Figure 1 that the data gener-
ally aligns strongly with the BAU scenario (for most of the variables); while the data does not align
with the other two scenarios (Turner, 2012, Turner, 2008) (see Appendix 1).
The demographic variables displayed in Figure 1 continue to show the same comparisons as seen
in the thirty year review (Turner, 2008), so that population would peak somewhat higher than the
BAU by 2030, or later according to an extrapolation of the difference between the birth and death
rates. It is more evident now, however, that the crude death rate has leveled off while the birth
rate continues to fall, which are general trends seen in the three scenarios, albeit at different values.
Notably, the death rate reverses its monotonic decline and begins to climb in all scenarios within a
decade; signicantly so in the standard run (and comprehensive technology) scenario by 2020.
Outputs of the economic system (Figure 1) show trends mostly commensurate with the LTG
BAU. Importantly, any downturn in industrial activity due to the GFC has not been captured in the
historic data since these were only available to 2007. Nevertheless, the observed industrial output
per capita illustrates a slowing rate of growth that is consistent with the BAU reaching a peak. In
this scenario, the industrial output per capita begins a substantial reversal and decline at about 2015.
Observed food per capita is broadly in keeping with the LTG BAU, with food supply increasing only
marginally faster than population. Literacy rates show a saturating growth trend, while electricity
generation per capita (upper data curve) grows more rapidly and in better agreement with the LTG
model (Figure 1).
Global pollution measured by CO2 concentration is most consistent with the BAU scenario (Figure
1), but this ten year data update indicates that it is rising at a somewhat slower rate than that mod-
elled. This could be due to a number of factors, which cannot be separately identied in this analysis.
For instance, in comparison with the BAU model output, lower observed industrial output per
capita is consistent with lower observed pollution generation, though this effect will be offset by the
slightly higher observed population levels. It is also possible that the dynamics of persistent pollution
generation by different economic activities or assimilation in the environment are not parameter-
ized in the World3 model precisely in terms of actual CO2 dynamics (which is still a topic of active
research). In this possibility, the recent data are consistent with a slightly higher assimilation rate, or
alternatively, a lower pollution generation rate in the agriculture sector compared with the indus-
trial sector (since the relative rate of food production is greater than industrial output).
Figure 1. LTG BAU (Standard Run) scenario (dotted lines) compared with historical data from 1970 to 2010 (solid lines)—for demographic variables:
population, crude birth rate, crude death rate; for economic output variables: industrial output per capita, food per capita, services per capita (upper
curve: electricity p.c.; lower curves: literacy rates for adults, and youths [lowest data curve]); for environmental variables: global persistent pollution,
fraction of non-renewable resources remaining (upper curve uses an upper limit of 150,000 EJ for ultimate energy resources; lower curve uses a
lower limit of 60,000 EJ [Turner 2008]).
Regardless of the explanation, the level of global pollution is sufciently low (in all scenarios, and the
data) to not have a serious impact on the environment and human life-expectancy (Turner, 2008).
In contrast, of the two data curves of non-renewable resources remaining, the lower estimate
demonstrates a closer alignment with the BAU (while the upper estimate aligns well with the com-
prehensive technology scenario [Figure 1]). The lower estimate also shows a signicant fall toward
the point when the World3 model incorporates a growing diversion of capital toward the resource
sector in order to extract more difcult resources (50–60 per cent of the original resource; see
Meadows et al., 1974, gure 5-18). This is the primary cause of collapse in the BAU scenario, as
described above. The observed data is based on energy resources (see discussion in Turner 2008,
pp. 405-407), conservatively assuming full substitution potential among the different primary energy
types. This assumption may not be entirely accurate (for instance, in the case of transport fuels (pri-
marily oil) essential for the smooth functioning of the economy). Subsequent sections reect upon
this question further.
Condence through calibration
The striking comparison described above indicates that the original LTG work should not be dis-
missed as many critics have attempted to do, and increases condence in the LTG scenario model-
ling. It is notable that there does not appear to be other economy-environment models that have
demonstrated such comprehensive and long-term data agreement. Nevertheless, this agreement is
not a complete validation of the model (partly due to the non-linear nature of the World3 model)
or the BAU scenario. Achieving validation requires at least that key inputs and non-linear (or
threshold) assumptions also be veried. This verication is partially initiated below with an examina-
tion of the imposts of resource extraction.
Despite the non-linearity of the World3 model, the general outcomes of the scenarios are not
sensitive to reasonable uncertainties in key parameters (Meadows et al., 1974). Nevertheless, critics
continue to question the value of the LTG modelling based on perceived model sensitivity (Castro,
2012). Supercially, early sensitivity analysis of the World3 model (de Jongh, 1978, Vermeulen and de
Jongh, 1976) appeared to show that the model is sensitive to parameter changes. For example, by
imposing a 10 per cent change from 1970 onwards to three parameters in the industrial sector it
is possible to alter signicantly the trajectories of the World3 output. In reproducing this change, I
found that the outcome was not avoidance of overshoot and collapse, contrary to the critics’ claim
(Turner, 2013). Instead, a wider examination of outputs indicates that overshoot and collapse was
simply delayed, and that the underlying reason for this was that industrial output per capita (a proxy
for material wealth) remained constant for decades before declining. In effect, the critics were actu-
ally creating elements of the ‘stabilized world’ scenario where material consumption was restrained,
but they did not acknowledge this.
Further, claims of parameter sensitivity evidently contradict the forty year alignment of the LTG
model with independent data; if the model was over-sensitive it should not successfully forecast
outcomes. The key to resolving this apparent paradox is to recognise that the World3 model was
calibrated as a whole system against data and trends from 1900 to 1970. This calibration is not sim-
ply inferring parameter values from the available data—which is recognised by everyone including
the LTG authors to incorporate sizable uncertainties—but more importantly that the various model
outputs (population, food, resources, etc.) must simultaneously produce reasonable values against
observed data. One sub-system of the model may work as an effective check on other sub-systems.
The whole-system calibration then constrains the collected values that parameters can have. This is
not to say that any single parameter is now known more accurately, which they are not. Rather, it is
the collection of interactions that matters. This is a key point that Bardi (2011) makes in his review
of earlier criticisms of the LTG (ie. the importance of treating a system as a whole and not isolating
sub-systems without reference to the rest of the system).
Additionally, there are general principles of control systems which apply despite parameter sensi-
tivity or uncertainty around the specics of future system trajectories. It is a general property of
systems with self-reinforcing and self-correcting mechanisms (ie. positive and negative feedbacks, the
former producing growth) that they will overshoot their long-term equilibrium if there are sufcient
delays in recognising or responding to the negative signals. Should this be the case, it is inevitable
that the system will “correct” by falling or collapsing below that equilibrium.
Is collapse likely, and imminent?
Examining mechanisms behind the near-term BAU
Based simply on the comparison of observed data and the LTG scenarios presented above, and given
the signicantly better alignment with the BAU scenario than the other two scenarios, it would
appear that the global economy and population is on the cusp of collapse. This contrasts with other
forecasts for the global future (eg. Raskin et al., 2010, Randers, 2012), which indicate a longer or
indeterminate period before global collapse; Randers for example forecasts collapse after 2050,
largely based around climate change impacts, with features akin to the LTG comprehensive technol-
ogy scenario. This section therefore examines more closely the mechanisms behind the near-term
BAU collapse and explores whether these resemble any real-world developments.
Real world developments—Peak Oil
Having conrmed the signicant alignment of 40 years of data with the BAU scenario, and estab-
lished that the model is not inappropriately sensitive, this section now considers whether the key
dynamics underlying the breakdown described above resemble actual developments. Since the col-
lapse in the BAU scenario is predominantly associated with resource constraint and the diversion
of capital to the resource sector, it is pertinent to examine peak oil (or other resource peaks). Peak
oil refers to the peak in production of oil (particularly from conventional supply), as opposed to
demand which is generally assumed to increase. Publications on peak oil have ourished in recent
years as the possibility of a global peak has become more widely accepted (eg. by the otherwise
conservative International Energy Agency) (Alexander, 2014). These publications tend to focus
on the question of when the peak will occur and what the oil supply volume will be. Sorrel et al.
(2010a, 2010b) review many of these and nd that independent researchers generally expect peak-
ing to occur within about a decade, or to have occurred recently (Sorrell et al. 2010a, Sorrell et al.
2010b, Murray and King, 2012); estimates of peaking made by oil industry representatives tend to be
decades away. Unfortunately, these oil production proles themselves say little analytically about the
implications of reduced oil supply rates on the economy, though qualitatively a constrained supply
of ubiquitous transport fuel is likely to be deleterious to the global and national economies (Hirsch,
2008, Friedrichs, 2010).
It is useful to compare the general qualities of past and future oil production with that inferred
from the LTG BAU output (Figure 2), even though there is inevitable uncertainty around individual
forecasts of oil production. The LTG production rate was derived by taking the rst derivative of the
non-renewable resource data.
The LTG curve approximates a “Hubbert-like” prole, depicted in Figure 2 using a logistic func-
tion (normalised to the same cumulative production ie. area under the curve). Hubbert assumed
a nite resource, with exponential growth in production in the early production phase (based on
data trends), and some mimic of discovery rates (ie. peaking and decline) leading eventually to zero
production (Hubbert, 1956). He originally drew arbitrary curves based on postulating peak produc-
tion rates, and estimates of ultimate resource. Subsequently, Hubbert used the more mathematically
convenient logistic function (for cumulative production) to capture the qualitative properties of
production proles (Hubbert, 1982).
In comparison, oil production rates from actual and projected data do not peak and fall so rapidly,
although the data supercially indicate a much lower peak as a result of the “accelerated” produc-
tion or earlier peak between 1960 and 1985. The extra production (relative to LTG) in this period
very closely matches the deciency in production (relative to LTG between 1990 and 2005). Indeed,
the cumulative production at 2005 is just 1 per cent different. The projection of oil production is
based on an empirical model of production lagging discovery (Gargett and BITRE, 2009), where
cumulative production cannot be greater than cumulative discoveries. Therefore, if discoveries have
peaked and fallen, production must also do so, though the actual rates can of course differ. It takes
no account of the how demand might vary, in contrast to the LTG.
Figure 2. Oil production rate: actual and projection; derived from the LTG; and a “Hubbert-like” curve based on a logistic function - all normalised to
equal total resource (ie. area under the curves).
Unlike other projections of oil production, the LTG curve is not hardwired explicitly in the model,
but is an outcome of other dynamics. Exponential growth occurs initially because of the demand
from exponentially growing industrial activity. Production subsequently falls due to the collapse in
demand from industrial activity (see next section). Production of non-renewable resources in the
World3 model scales with population using a per capita resource usage multiplier, and the latter
is an increasing (approximately linear) function of industrial output per capita. Consequently, the
production rate follows the industrial output.
Notably the oil resource has not run out when the global collapse begins; far from it, since the peak
extraction rate occurs about halfway through the resource pool. Further, as respected commenta-
tors (The Economist and The Guardian) point out, there are immense additional pools of fuels in the
form of unconventional oil and gas reserves, such as those being accessed by hydraulic fracturing
(fracking) (Maugeri, 2012). (These additional reserves were included in the data of non-renewable
resources for the comparison shown in Figure 1). The optimistic view being expressed recently
is that there could be a new oil and gas glut. This supercially appears to contradict the resource
constraint that underpins the collapse in the BAU scenario of the LTG .
But the protagonists of oil and gas gluts have not understood a crucial point. They have essentially
confused a stock with a ow. The key, as the LTG modelling highlights, is the rate at which the re-
source can be supplied, ie. the ow, and the associated requirements of machinery, energy and other
inputs required to achieve that ow. Contemporary research into the energy required to extract
and supply a unit of energy from oil shows that the inputs have increased by almost an order of
magnitude. It does not matter how big the resource stock is if it cannot be extracted fast enough or
other scarce inputs needed elsewhere in the economy are consumed in the extraction. Oil and gas
optimists note that extracting unconventional fuels is only economic above an oil price somewhere
in the vicinity of US$70 per barrel. They readily acknowledge that the age of cheap oil is over, with-
out apparently realising that expensive fuels are a sign of constraints on extraction rates and inputs
needed. It is these constraints which lead to the collapse in the LTG modelling of the BAU scenario.
The end of easy oil, and subsequent global collapse
Consequently, what is more relevant than the oil supply rates per se to our analysis of the LTG and
collapse is the “opportunity cost” associated with extracting diminishing supplies of conventional oil
or difcult extraction of non-conventional oil (eg. tar sands, deep water, coal-to-liquids, etc.) (Mur-
ray and King, 2012). In the LTG, the fraction of capital allocated to obtaining resources (FCAOR)
represents this opportunity cost. In the peak oil literature, the relevant measure of opportunity
cost is the energy return on investment (EROI) which is related to the net energy available after
energy is used extracting the resource (Heun and de Wit, 2012, Dale et al., 2011, Heinberg, 2009,
Murphy and Hall, 2011). The EROI is dened as the ratio of gross energy produced, TEProd, to energy
invested to obtain the energy produced, ERes.
The EROI can be related to the FCAOR used in the LTG. Since the capital (machinery eg., pumps,
vehicles) operated in the resource sector, CRes, is basically representative of the overall machinery
stock, CTtl, the energy intensities will be similar and therefore the ratio of capital can be approximat-
ed by the ratio of energy used in the resource sector, ERes, to total energy consumed, TECons.
Since the total energy consumed in any year will be approximately equal to the total energy pro-
duced (because stocks of energy stored are relatively small and don’t change signicantly from year
to year) TECons ≈ TEProd, then equations 1 and 2 give:
The collated data and model of EROI in Dale et al. (2011) can therefore be converted to FCAOR at
corresponding values for the fraction of the oil resource remaining. This can be then be compared
against the data used in the LTG (eg. shown in Meadows et al., 1974, gure 5-18). If the peak of
conventional oil has occurred, or is about to occur, then approximately half the resource has been
consumed, ie. non-renewable resource fraction remaining, NRFR ≈ 0.5. Contemporary estimates of
EROI are in the range 10-20 (or 1/EROI of 0.1-0.05). This agrees with the values and trends of the
key parameter, FCAOR, used in the LTG (see Figure 3).
Therefore, in addition to the data comparison made for modelled outputs, this data on oil resource
extraction corroborates a key driver of dynamics in the LTG BAU scenario. In other words, in addi-
tion to outputs of the model aligning with data, the key mechanism driving the collapse in the BAU
is also observed in real world data.
energy return on (energy) invested =
fraction of capital allocated to obtaining resources ss
= = ≈
The limited role of alternative energy innovation
Given that the key mechanism underlying collapse in the BAU scenario is evidently the diversion
of capital toward extracting depleting resources, it is pertinent to examine the sensitivity of the
scenario to changes in this factor. In the case of oil (and gas) resources in particular, could it be that
the current expansion of unconventional resources (tight oil, shale oil and gas, tar sands, etc.) is suf-
cient to offset the decline in production of conventional oil? Critics of unconventional resources
point toward decreasing net energy due to the difculty of extraction. In terms of the LT G model-
ling, this relates to the fraction of capital allocated to obtaining resources (FOCAR) increasing as
the resource stock reduces (such as in the BAU setting). However, it is early days in the new play of
unconventional resources, so it would be reasonable to anticipate that cumulating experience and
new technologies will ease the extraction task and hence reduce the energy/capital required for
each barrel of oil. This possibility has been tested in the World3 model, using the setting (testFO-
CAR) shown in Figure 3.
Figure 3. Increased efciency in extraction of unconventional resources (blue curve) as the fraction of resource declines toward zero, compared with
the BAU setting (red).
Figure 4. Collapse delayed by about 2 decades, but is worse (ie. a “Seneca cliff”), due to increased efciency in accessing unconventional resources.
The alternative FOCAR is held at current levels and even slightly decreased (to half-way between
the original 5 per cent and current level) to simulate the effect of cost saving technologies. But as
the resource remaining approaches 10 per cent, the extraction effort increases and must approach
a FOCAR of 1 as the resource is exhausted (the value of 1 actually prevents the non-renewable
resource from being completely exhausted because the economic costs of harvesting resources ef-
fectively slows the resource extraction rate). This type of FOCAR was also tested by the LTG team
(see pp. 398–405 Meadows et al., 1974) among other sensitivity tests.
However, collapse is not avoided but simply delayed by one to two decades (Figure 4), and when
it occurs the speed of decline is even greater. Easier to obtain resources permit economic growth
to be re-kindled following a relatively minor hiatus at about 2015. Subsequently, the draw-down of
non-renewable resources continues apace, and reaches such a low level that the industrial system
cannot be supported and output drops rapidly at about 2030. As a result, population grows a little
higher than the BAU, but falls from about 2035 at a faster rate and to a lower level.
Contemporary impacts of oil constraints: is collapse
The close alignment between the LTG BAU scenario and observed developments over the last four
decades, as well as the correspondence in the underlying dynamics described above, portend of po-
tential global collapse. Although the general commentary on the LTG describes collapse occurring
sometime mid-century (and the LTG authors stressed not interpreting the time scale too precisely),
the BAU scenario implies that a relatively rapid fall in economic conditions and the population
could be imminent. Indeed, other aspects of oil supply constraints explored in the following, indicate
that the ongoing economic downturn of the GFC may be representative of an imminent BAU style
Firstly, oil price rises have been linked to recent increases in food prices (eg. (Alghalith, 2010, Chen
et al., 2010). There are direct and indirect links between oil and food (Schwartz et al., 2011, Neff
et al., 2011), associated with fuel for machinery and transport, both on-farm and in processing and
distribution, as well as feedstock for inputs such as pesticides. Also, although nitrogen fertilizer is
largely manufactured from natural gas, the price of these commodities is also linked to that of oil.
More recently, production of bio-fuel as an alternative transport fuel, such as corn-based ethanol,
has displaced food production and has been a factor in food price increases (eg. Alghalith, 2010,
Chen et al., 2010). These developments resemble the dynamics in the LTG BAU scenario where
agricultural production is negatively affected by reduced inputs. There may also be evidence of global
pollution beginning to impact food production (which is a secondary factor in the BAU scenario) in
the recent occurrence of major droughts, storms and res (eg. Russia, Australia) that are potentially
early impacts of global climate change driven by anthropogenic greenhouse gas emissions.
The role of oil (and food) prices extends further, into more general economic and political shocks.
For instance, other aggregate modelling of the role of energy in the economy (Nel and Cooper,
2009) nds that energy constraints cause a long-term economic downturn, as well as reducing
greenhouse gas emissions, which are similar outcomes to those in the LTG collapse. Empirically,
there is clear evidence (eg. Murray and King, 2012, overviews in Murphy and Hall, 2010, Murphy
and Hall, 2011) of a connection between many oil price increases and economic recessions (just as
there exists a strong correlation between energy consumption and growth in economic indicators).
Hamilton’s econometric analysis (2009) indicates that the latest (US) recession, associated with the
GFC, was different from previous oil-related shocks in that it appears caused by the combination of
strong world demand confronting stagnating world production. His analysis downplays the role of
Nevertheless, the overriding proximate cause of the GFC is evidently nancial: excessive levels of
debt (relative to gross domestic product (GDP), or more accurately, the actual capacity of the real
economy to pay back the debt) (Keen, 2009). Such nancial dynamics were not incorporated in the
LTG modelling. Das (2011) highlights correlated defaults in high-risk debts, such as sub-prime hous-
ing mortgages, as a key trigger of the GFC. The nancial models used did not properly account for
a high number of defaults occurring simultaneously, being based on statistical analysis from earlier
periods which suggest less correlation in defaults. Correlation may be caused by specic aspects
of the nancial instruments created recently, including for example, adjustments upward in inter-
est rates of sub-prime mortgages after an initial “teaser” period of negligible interest rates. Even so,
some spread in defaults would be expected in this case. Alternatively, another potential factor could
be the price increases in oil and related commodities, which would be experienced by all house-
holds simultaneously (but with a disproportionate impact on large numbers of households with low
discretionary income) and hence cause the coordinated debt defaults.
Regardless of what role oil constraints and price increases played in the current GFC, a nal con-
sideration is whether there is scope of a successful transition to alternative transport fuel(s) and
renewable energy more generally. Due to the GFC, there may be a lack of credit for funding any
coordinated (or spontaneous) transition (Fantazzini et al., 2011). And economic recovery may be
interrupted, repeatedly, by increased oil prices associated with any recovery. Additionally, even if
a transition is initiated it may take about two decades to properly implement the change over to
a new vehicle eet and distribution infrastructure (Hirsch, 2008, Hirsch et al., 2005). To transition
requires introducing a new transport fuel to compensate for possible oil production depletion rates
of four per cent (or higher) while also satisfying any additional demand associated with economic
growth. It is unclear that these various conditions required for a transition are possible.
The role of social responses
In terms of social changes, it is pertinent to note that while the authors of the LTG caution that
the dynamics in the World3 model continue to operate throughout any breakdown, different social
dynamics might come to prominence that either exaggerate or ameliorate the collapse (eg. reform
through global leadership, regional or global wars). Other researchers have contemplated how
society might respond to serious resource constraints (eg. Friedrichs, 2010, Fantazzini et al., 2011,
Heinberg, 2007, Orlov, 2008, Heinberg, 2011). Various degrees of hostility are foreshadowed, as well
as lifestyles in developed countries that revert to greater self-reliance.
The dynamics in the World3 model leading to collapse resonate with aspects of other conceptual
accounts of failed civilizations (Tainter, 1988, Diamond, 2005, Greer, 2008, Greer, 2005). Tainter’s
proposition of diminishing returns from growing complexity relates to the increasing inefciency of
extracting depleting resources in the World3 response. It also aligns with a more general observa-
tion in the LTG that successive attempts to solve the sustainability challenges in the World3 model,
which lead to the comprehensive technology scenario, result in even more substantial collapse. The
existence in World3 of delays in recognising and responding to environmental problems resonates
with key elements in Diamond’s characterisation of societies that have failed. And Greer’s mecha-
nism of “catabolic collapse” - ie. increases in capital production outstripping maintenance, coupled
with serious depletion of key resources - describes in a slower mode the core driver of breakdown
in the LTG B AU.
Unfortunately, scientic evidence of severe environmental or natural resource problems has been
met with considerable resistance from powerful societal forces, as the long history of the LTG and
international UN initiatives on environmental/climate-change issues clearly demonstrate. Somewhat
ironically, the apparent corroboration here of the LTG BAU implies that the scientic and public
attention given to climate change, whilst tremendously important in its own right, may have del-
eteriously distracted from the issue of resource constraints, particularly that of oil supply. Indeed,
if global collapse occurs as in this LTG scenario then pollution impacts will naturally be resolved—
though not in any ideal sense! A challenging lesson from the LTG scenarios is that global environ-
mental issues are typically intertwined and should not be treated as isolated problems. Another
lesson is the importance of taking pre-emptive action well ahead of problems becoming entrenched.
Regrettably, the alignment of data trends with the LTG dynamics indicates that the early stages of
collapse could occur within a decade, or might even be underway. This suggests, from a rational risk-
based perspective, that we have squandered the past decades, and that preparing for a collapsing
global system could be even more important than trying to avoid collapse.
Updates to the historical data
The data presented here follows that of the thirty year review (Turner, 2008). This data covers the
variables displayed in the LTG output graphs: population (and crude birth and death rates); food sup-
ply per capita; industrial output per capita; services per capita; fraction of non-renewable resources
available; and persistent global pollution. Data sources are all publically available, many of them
through the various United Nations organisations (and websites). Details were provided earlier
(Turner, 2008) on these data sources and aspects such as interpretation, uncertainties and aggrega-
tion. However, some additional data and calculation were necessary since measured data to 2010
was not always available (and even when it is the data may be forecast estimates). A summary of the
data is provided in the following.
Population data is readily available from the Population Division of the Department of Economic
and Social Affairs of the UN (United Nations) Secretariat (obtained via the online EarthTrends
database of the World Resources Institute); but data from 2006 onwards is a forecast. Given the
short gap to 2010 and typical inertia in population dynamics, the 2010 estimate will be sufciently
accurate for the comparison made here.
Food supply was based on energy supply data (calories) from the Food and Agriculture Organisa-
tion (FAO), with the extension to 2009/10 generated from comparison with production data, which
was scaled to the energy supply data for each corresponding food type in the production data.
Industrial output was available only to 2007 directly from the UN Statistical Yearbooks (UN 2006,
2008), now accessible online. Industrial output per capita is used as a measure of material wealth in
the LTG modelling, but the industrial output also supplies capital for use in other sectors, including
agriculture and resource extraction.
Service provision (per capita) has been measured by proxy indicators: electricity consumed per
capita and literacy rates. In the former case, for the most recent data it was necessary to scale
electricity generation data (from BP Statistical Review 2011) to consumption values and hence
account for electricity transmission losses. Literacy rates were updated from the United Nations
Educational, Scientic and Cultural Organisation (UNESCO) Statistics database, which is the source
for the EarthTrends data. Literacy rates provide a partial proxy indicator since they will saturate as
they increase toward 100 per cent. Values are provided for time ranges rather than single years.
The fraction of non-renewable resources available is estimated from production data on energy
resources, since other resources are conservatively assumed to be innitely substitutable or there
to be unlimited resources. Energy production data to 2010 was obtained from the BP Statistical
Review (2011), which was subtracted from the ultimate resource originally available to obtain the
remaining resources. To account for considerable uncertainty in the ultimate resource, upper and
lower estimates were made based on optimistic and constrained assessments, respectively (Turner,
2008). Hence, two data curves are provided for the fraction of non-renewable resources remaining.
Finally, global persistent pollution was measured by the greenhouse gas CO2 concentration, avail-
able to 2008 on the EarthTrends database, with latest measurements to 2010 from Pieter Tans, Na-
tional Oceanic and Atmospheric Administration (NOAA) Earth System Research Laboratory (ESRL),
and Ralph Keeling, Scripps Institution of Oceanography.
Data comparison with three bounding scenarios
To help convey how signicant is the strong alignment of data with the BAU or “standard run” sce-
nario, with this expands the comparison to two other key scenarios from the LTG modelling, namely
the “comprehensive technology” and “stabilized world” scenarios. The three scenarios together
effectively present a bounding envelope for the full spectrum of scenarios produced.
The comprehensive technology scenario attempts to solve sustainability issues with a broad range
of purely technological solutions. This technology-based scenario incorporates levels of resources
that are effectively unlimited, 75 per cent of materials are recycled, pollution generation is reduced
to 25 per cent of its 1970 value, agricultural land yields are doubled, and birth control is available
For the “stabilized world” scenario, both technological solutions and deliberate social policies are
implemented to achieve equilibrium states for key factors including population, material wealth,
food and services per capita. Examples of actions implemented in the World3 model include: per-
fect birth control and desired family size of two children; preference for consumption of services
and health facilities and less toward material goods; pollution control technology; maintenance of
agricultural land through diversion of capital from industrial use; and increased lifetime of industrial
i One particularly important case in point is the change from elastic to inelastic supply of oil and
the resulting economic implications (Murray and King, 2012, Murray and Hansen, 2013), which are
discussed in detail in later sections.
The statistical analysis undertaken in our 30-year review (Turner, 2008) was not reproduced here
as the changes would be minor, and add little further to the assessment.
iii http://earthtrends.wri.org (source: www.un.org/esa/population/ordering.htm)
v UN 2006, table 5, p. 22, UN 2008, table 5, p. 14. http://unstats.un.org/unsd/syb/
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