Due to thermodynamic constraints, all economic activities ultimately depend on the transformation of energy into useful work; ever since the dawn of the industrial revolution, the demand for energy has grown exponentially across all societal sectors, from manufacturing to transportation, housing, and agriculture, with the vast majority of that energy being sourced from fossilized carbon deposits of various nature (initially coal, then conventional oil and gas, and more recently also fracked light tight oil and tar sands).

Transforming these fossil fuels into usable energy carriers, and ultimately work via combustion, has been, and still is, directly responsible for massive anthropogenic greenhouse gas emissions, which have triggered unprecedentedly rapid global climate change (IPCC 2022). At the same time, global access to increasingly vast quantities of energy has also enabled the rampant exploitation and depletion of a whole range of material and ecosystem resources, with ensuing severe environmental degradation, in terms of biodiversity loss, overfishing, deforestation, soil erosion, plastic pollution, wide-spread eco-toxicity, ozone layer depletion, soil and ocean acidification, etc. This increasingly more problematic state of matters has been likened to the simultaneous approaching and, in some cases, crossing of multiple “planetary boundaries” (Rockström et al. 2009; Steffen et al. 2015).

In light of all of the above, it is unsurprising that the investigation of the range of possible future energy scenarios that might unfold over the next decades has become one of the most prolific and hotly debated areas of research. However, among a multitude of alternative perspectives, reflecting the viewpoints and informed opinions of international organizations and various industrial actors and stakeholder groups, when specifically perusing the latest scientific literature in this field, it emerges that several academic authors have increasingly positioned themselves (either explicitly or implicitly, but often equally unmistakably) within either of two seemingly ideological “camps”. These may be broadly characterized as, respectively, that of the “systemic pessimists” (i.e., authors who champion concepts such as carrying capacity, overpopulation, overshoot, peak oil and peak resources, but who often downplay or even dismiss the potential of renewable energies) and that of the “technological optimists” (i.e., authors who mostly tend to focus on the rapid advancements in renewable energy technologies and the promise that these hold to decarbonize future societies, while often failing to address the broader context of other bio-physical planetary limits). While proponents of both camps often bring valid arguments and evidence to the table to support their viewpoints, they often seem to summarily dismiss the arguments and evidence put forth by the other camp, thereby ultimately allowing the discourse to degenerate into an unhelpful and, arguably, un-scientific “us vs. them” contest. In fact, this is not the first time that the emergence of counterproductive tribalism in scientific, and specifically energy policy, debate has been observed: for instance, “Business as Usual” vs. “Middle of the Road” vs. “Radical Change Now” (Thompson 1984); “green growth vs. de-growth” (Hickel and Kallis 2020); “techno-optimists vs. techno-realists” on economic axis, “renewables vs. fossil” on energy axis (King 2021).

This article aims to first delineate and discuss the main arguments put forth by the two aforementioned “camps”, and then suggest a way forward to overcome such counterproductive confrontation.

No Infinite Growth on Finite Resources

The original notion of a fundamental mismatch between unconstrained economic growth and the ultimately finite resources of the Earth dates back to the very early days of the industrial revolution, when Malthus first logically speculated that an exponentially growing population, initially made possible by increased access to resources, would eventually outpace resource availability, and thus ultimately lead to catastrophic collapse (Malthus 1798). One and a half centuries later, well into the age when petroleum oil had already established itself as the main primary energy resource supporting economic growth, Hubbert introduced the concept of “peak oil” (Hubbert 1956) (although this actual catchy phrase was coined only years later), warning that at the then current rate of extraction, global oil production would soon peak, and then inexorably and irreversibly decline (while Hubbert had not accounted for the later exploitation of non-conventional oil reserves, his predictions still appear to fundamentally hold, even if shifted forwards by a few years (Bardi 2018; Laherrère et al. 2022). In the 1970s, the Club of Rome (a group of current and former politicians, United Nations administrators, diplomats, scientists, economists, and business leaders from around the globe) commissioned the famous report “The limits to growth” (Meadows et al. 1972), in which the consequences of unconstrained population and economic growth were quantitatively investigated by means of a computer model based on five key interdependent variables: population, agricultural production, non-renewable resource depletion, industrial output, and pollution generation. Widespread and long-lasting debate and controversy ensued on many details about the model structure, parameters, and assumptions, but the key message was clear, and it was essentially found to still hold by several other authors who reviewed and updated the calculations (Bardi 2011; Herrington 2020; Hall 2022): the Earth’s system is incapable of supporting infinite population and economic growth because of the finite nature of its natural resources.

Over the four decades since that seminal report, the fundamental issue of the impossibility of infinite growth on finite resources has continued to be elaborated upon by a varied community of scientists sharing an interest in the new disciplines of ecological economics and bio-physical economics, which—contrary to conventional and neoclassical economics—emphasize the key supporting roles of energy and bio-physical resources, and reject the proposition that human-made monetary capital can substitute for natural capital (bio-physical economics is the more recent of the two, and was born in the 2010s in response to the perception that many ecological economists still had some remaining commitment to neoclassical models and the role of markets). Among the most noteworthy contributions to this on-going discussion are perhaps Rees and Wackernagel’s quantitative concept of “ecological footprint” (Rees 1992) and their popularization of the term “overshoot”, and Odum’s suggestion that the only way for humankind to continue to flourish will be to embark on a “prosperous way down” (Odum and Odum 2001), where people must adapt to a future with vastly increased competition for energy and resources by essentially learning to live with less (aided in part by technology, but primarily via a fundamental restructuring of how societies operate).

More recently, a range of authors have taken it upon themselves to reaffirm these fundamental concepts within the specific context of future energy scenarios. But a new dimension to the discussion had been added in the interim, as various independent studies, often based on life cycle assessments (LCA), had started to appear, pointing to high energy return on investment (EROI) of renewable energies, and specifically photovoltaics (PVs). By some, these results were interpreted as undermining the very foundations of the concepts discussed above, for if renewable energy were indefinitely viable then perhaps the “limits to growth” could be postponed indefinitely. As a result, what was originally a discussion about finite resources in a more general sense, started turning into much more specific arguments about issues like what is the proper EROI for PVs and/or other renewables; broadly speaking, the debate on the ultimate possibilities of renewable energies became unhelpfully conflated with whether or not there are limits to growth.

As a first example, in chronological order, of when this trend started to appear, in a 2009 article (Hall and Day 2009), Hall and Day first convincingly argued that the world would be well-advised to pay renewed attention to those same warnings about the limits to growth made in the eponymous report three and a half decades earlier. However, towards the end of the same paper, they then also included a figure comparing EROIs of a wide range of renewable vs. non-renewable energy resources. That figure reported comparatively low values for renewables, while failing to clarify whether consistent boundaries and assumptions had been applied across the board, both in terms of which stages of the supply chains were included and which were not, and in terms of the point-of-use fungibility of the associated energy carriers (e.g., thermal fuels vs. electricity). When compounded by somewhat simplistic extrapolations and assumptions about the future continued dependence on fossil primary energies, the study’s conclusions specifically on renewable energies and their potential to contribute to future societies ultimately appeared to lack robustness.

The more general issue of boundaries in comparative net energy/EROI analyses has been elaborated on elsewhere (Raugei 2019; Murphy et al. 2022); while the specific approaches to resolve methodological inconsistencies proposed in these, and other, papers are of course subject to further scientific scrutiny and debate, the fundamental importance of carefully considering potential sources of methodological distortion and unintentional bias in comparative assessments remains undisputable, and especially so when such assessments are intended to inform energy policy scenarios for the future.

In subsequent papers, other authors raised specific criticisms about PV’s supposedly insufficient ability to deliver net energy to societies (Weißach et al. 2013; Ferroni and Hopkirk 2016). These studies attracted considerable attention within and beyond academia; however, they were also criticized for being lacking in terms of methodological rigour and internal consistency when attempting comparisons across different technologies (Raugei et al. 2015, 2017), which cast doubt on the validity of their take-home messages. One even more recent paper, co-authored by the same Rees who co-originated the concept of ecological footprint, purported to highlight “cracks in the foundation of the mainstream energy transition narrative”, while denigratingly referring to wind and PV as “so-called renewables” (Seibert and Reese 2021). However, this paper too was subsequently criticized as insufficiently thorough and rigorous in its use of pre-existing data, thereby leading to a lack of robustness in its numerical findings, and hence also potentially in the ensuing strongly worded conclusions (Diesendorf 2022; Fthenakis et al. 2022). It is noteworthy that the same paper also led to a rare apology by the editor-in-chief of the journal, for failing to request key corrections prior to publication (Sciubba 2022).

What appears to be the common thread linking these and other similarly critical essays on the energy transition is that, while the authors’ core arguments about the fundamental inescapability of the limits to growth and the ensuing need to fundamentally re-think the currently dominating economic paradigm are well-founded and remain fundamentally unassailable, their analyses are often let down by insufficient attention to detail and rigour when specifically carrying out quantitative assessments of renewable energies, often leading to rushed conclusions on these technologies that have been questioned as not standing up to close scrutiny. In fact, some of these authors (e.g., Seibert and Reese 2021) have tended to paint renewable energies as a pernicious distraction from the key issue of global overshoot of the Earth’s carrying capacity, therefore also brushing aside any suggestion of renewable energies’ ability to significantly reduce global warming and environmental degradation (vs. the continued use of fossil fuels).

Unfortunately, and independently of the authors’ original intentions, this practice then leads to some of these studies being instrumentally cited, and even brandished as vindication by a range of actors with vested interests in fossil fuels and other clearly unsustainable alternatives.

The Promise of the Renewable Energy Transition

Since the mid-1970s, the scientific literature has also featured a large number of studies that have investigated the viability of future renewable energy transition scenarios on the global scale. Interest in this topic surged after the publication of two widely cited articles by Fthenakis et al. (2009) and Jacobson et al. (2011), which have been followed by many more by various authors (Jacobson et al. 2017a, 2017b; Raugei et al. 2018, 2020; Aghahosseini et al. 2019; Bogdanov et al. 2021a, 2021b; Olabi and Abdelkareem 2022). A recent and comprehensive review of the literature in the specific field of 100% renewable energy scenarios is provided in Breyer et al. (2022).

While not always immune from vibrant criticism and controversy (e.g., (Jacobson et al. 2015) criticized by (Blistine and Blanford 2016) and (Clack et al. 2017), with subsequent rebuttals by the original authors (Jacobson et al. 2016, 2017a, 2017b)), broadly speaking, these studies have tended to be characterized by a high degree of scientific rigour and attention to detail in terms of the latest developments in renewable energies and their industry-vetted roadmaps for the next decades, leading to robust results. Even so, an important distinction needs to be made between verification (whereby the energy scenario models are subject to a thorough internal check to ensure logical rigour and bug-free operation) and validation (whereby the models results are externally checked vs. the observed reality) (Sargent 2010). Clearly, while the former is achievable via due scientific diligence, the latter remains inescapably elusive for all future-oriented studies, which calls for exercising some caution when interpreting the results and drawing conclusions.

But even more important is the fact that authors of 100% renewable energy studies have often shied away from directly addressing the larger question of what it would ultimately take to lead the world down a path that may be truly sustainable in the long term, focussing instead primarily on the very important, but more reduced-scope, issue of the decarbonization of the energy sector (and in some cases, of the closely related transport sector, too). In so doing, these authors have arguably erred on the opposite side vs. those in the “systemic pessimistic camp”, and, perhaps inadvertently, they have often ended up painting a too-rosy picture of a future in which switching from fossil fuels to renewable energies is implied to suffice to solve not only climate change but essentially all environmental problems.

In other words, these “technological optimistic” authors may have studiously and rigorously investigated the potential of renewable energies to deliver modern societies from the grip of fossil fuels, but they have failed to consider the wider issues that would continue to affect the world, even in a future world largely supported by renewable energies. In fact, the hitherto dominating paradigm of unfettered growth in material consumption and rampant exploitation of many natural and ecosystem resources is incompatible with fundamental bio-physical constraints (Rockström et al. 2009; Steffen et al. 2015), and it remains ultimately unsustainable irrespective of which energy resources are used to power it.

Conclusion: A Dire Need for a “Middle Way”

The observed trend towards the delineation of two opposed ideological positions, here respectively referred to as “systemic pessimism” and “technological optimism”, clearly hinders the impartial assessment of the effectiveness (or otherwise) of the available renewable energy transition strategies, in terms of mitigating climate change and overall environmental and ecosystem degradation. The authors that appear to subscribe to the first ideology raise valid arguments about the limits to growth and about the ultimately unsustainable consequences of unconstrained access to and continued growth in use of energy (irrespective of whether it be from renewable or non-renewable resources), because of the ensuing multiple pressures on ecosystems and planetary boundaries. However, in so doing they also unnecessarily and unhelpfully dismiss the mounting evidence that points to the technical viability of renewable energy technologies and their significant potential, on a global scale, to bring about a much-needed reduction, and possibly even a complete end, to the use of climate-threatening fossil fuels. Conversely, those other authors that focus more narrowly on the technical feasibility of renewable energies, and who, based on their encouraging findings, are vocal advocates for their rapid deployment on the global scale, then often eschew addressing the “elephant in the room” represented by the limits to growth (which ultimately still hold regardless of the possible success of a renewable energy transition). In so doing, the strength of their arguments risks being justifiably overshadowed by accusations of excessive “technological optimism” and “tunnel vision”.

Thus, the current polarization of views points to a false dichotomy that risks devaluing both positions, and it trivializes what should instead be the most important research questions of all, namely: to which extent a more sustainable future is indeed possible, and which systemic changes (including, but not limited to, phasing out fossil fuels) will be required to achieve it. The regrettable missed opportunity represented by such a lack of genuinely constructive scientific debate is further laid bare in the context of the recent fossil energy price crisis induced by the on-going (at the time of writing) war in Ukraine.

In a few, regrettably still isolated cases, some authors have attempted to bridge this counterproductive communication gap and argued for a more balanced approach to energy futures and sustainability studies. One such instance is provided by a recent paper by Floyd et al. (2020a), in which the authors state: “There is a broad middle-ground, though, who support the transition to renewable energy to whatever extent is possible, and who at the same time regard the nature of future energy systems—and, often, the forms of economy and society that they enable—as open questions”. Although some aspects of that paper were not immune from criticism and controversy (Diesendorf et al. 2022; Floyd et al. 2020b), it is argued here that this kind of approach to scientific inquiry is, in principle, clearly a step in the right direction.

The scope of the discussion then needs to be broadened even further, and in so doing the scientific community would be much better served if such discussion were held without resorting to cherry-picking, oversimplification, “whataboutism”, and other diversion tactics that only end up making the various participants dig in deeper and deeper in what are often already deeply entrenched defensive positions.

Ultimately, it is high time to admit that both sets of core arguments loosely ascribed in this article to the two opposed ideological “camps” are probably simultaneously true, to some extent at least. And from this simple realization follows what should have been obvious all along, i.e., that adopting a more balanced “middle way” approach is the only truly sensible way forward for a healthy and genuinely scientific debate. Making genuine progress will then call for a combined set of skills from diverse disciplines, including energy analysis, life cycle assessment, computational modelling, and macro-level bio-physical economics.