Clarifying the driving forces behind our ecological crisis: a general model

In order to solve our ecological crisis, it is crucial to have a fair understanding of its background. In this article I integrate the most important driving forces of human transformation of the biosphere into a general model. First, I show that it is the economic subsystem of society that produces nearly all human transformation of the biosphere. Then I differentiate between direct driving forces, which are the number of people/households, the economic output per capita/per household, the environmental impact of technologies, the structure of the economy and the geographical pattern of the economy; and indirect ones, which are the mind of people, social institutions, biological factors and physical geographical features. The behavior of individuals, groups of people and organizations mediates between indirect and direct driving forces. The model also shows us the basic strategies of environmental sustainability. Cultural changes are needed to attenuate the direct driving forces. In turn, these changes will happen only if those desiring them will have enough power to reshape social institutions and the mind of people.


Introduction
What are the main driving forces behind our ecological crisis? The question is simple, but the answer is complex. Nevertheless, if our aim is to solve this crisis, it is crucial to have a fair understanding of its background. The thorough uncovering of the factors behind our ecological predicament is pivotal to the identification of the basic strategies of environmental sustainability.
The current ecological crisis (comprised of interwoven environmental problems such as global climate change, loss of biodiversity, soil degradation, smogs, toxic effects of synthetic chemicals etc.) is the result of excessive human transformation of the biosphere. 1 This means that our biosphere transforming activities are not necessarily problematic. By now, however, they have become so extended and accelerated that even our own well-being-as well as the existence of many other species-is already threatened.
In this article I try to integrate the most important driving forces of human transformation of the biosphere into a general model. The goal here is not the quantification of the particular driving forces or determining the relative role of these various factors, but gaining a better understanding of the causes of our ecological crisis and its potential solutions. The analysis will be done on the global scale, though it may be valid on smaller scales as well.
The model has its predecessors. It is built around the wellknown IPAT-formula (see below). Nevertheless, the formula is refined, developed and put in a wider context here.

Economic metabolism
Every living organism transforms the biosphere due to its own metabolism-this process is called niche construction (Odling-Smee et al. 2013;Laland et al. 2015). First, living creatures transform the biosphere by appropriating nutrients from it. Second, they also receive energy with these nutrients (heterotrophs) or able to capture external energy (autotrophs) to live their lives-this amount of energy (at least part of it) is available for them to transform the biosphere. Third, they also modify the environment by their waste products. Organisms that alter the biosphere the most are dubbed ecosystem engineers (Jones et al. 1994).
Humans are by far the most significant ecosystem engineers. It is because while the energy use of all other living organisms is limited to the amount they can appropriate by their metabolism and thus incorporate in their bodies, we are able to use extrasomatic energy sources too, ever since we learned to use fire. In the past millennia we managed to increase the amount of extrasomatic energy available for us to a great extent (Smil 2017;Takács-Sánta 2004). Nowadays we have diverse energy sources from fossil fuels through renewables to nuclear to create a huge amount of energy that can be used for our own goals.
To put it in another way, in the case of humans biological metabolism is complemented (and also overwhelmed by now) by economic metabolism driven by extrasomatic sources of energy. 2 All economic activities must begin with the extraction of natural resources in order to get raw materials and energy sources. And at the end point all economic activities generate wastes and pollution (Fig. 1). Basically, we created a huge animal called economy eating natural resources and defecating polluting materials and wastes (Daly 1993).
The three fundamental subprocesses of the economic process are the extraction of natural resources, the production of goods and services, and finally the consumption of them (Fig. 1). All of these subprocesses are aided by technology, which can be defined here as a system of means causing us to increase economic output by extending our biological abilities. In historical comparison, technologies of our time are especially complex and efficient, thus making us able to generate enormous economic output.

Direct driving forces
As we have seen, through the three fundamental economic subprocesses it is the economic subsystem of society that produces nearly all human transformation of the biosphere (beside the comparatively tiny amount caused by our biological metabolism). Hence, it is quite obvious that human transformation of the biosphere is a direct function of economic output: the more goods and services are produced, the more the biosphere is altered.
Nevertheless, it is also evident that environmental impact per unit of output can differ vastly. For instance, the same item can be produced by the use of recycled or non-recycled materials as well as energy-efficient or energy-wasting production technologies, etc. Hence, beside economic output, our transformation of the biosphere will be the direct function of another factor as well: the ecological efficiency of economic output. This factor comprises the transformation of the biosphere deriving from the use of natural resources (i.e., materials and energy) as well as from the waste and pollution arising during the generation of a unit of output.
All the above can be expressed in a simple formula: where B is the extent of human transformation of the biosphere (usually called "environmental impact"), Y is (total) economic output and Z is defined as transformation of the biosphere per unit economic output.

Deconstructing Y
What kind of factors influence economic output? Obviously, the number of people is one of them: roughly speaking more people need more goods and services. Therefore: where P is population size (the number of people) and O p is economic output per capita.
It is important to stress, however, that this is not the only way to deconstruct Y. It is possible, for instance, that the number of households determines the extent of transformation of the biosphere more directly than population size in itself (e.g., O'Neill et al. 2001;Keilman 2003;Liu et York and Rosa 2012). It is because the same number of people will have higher environmental impact if they are divided among more households, since, for instance, more equipment is needed, more homes are heated, etc. in this case. Thus, Y can be deconstructed also as: where H is the number of households and O H is economic output per household.
Accordingly, a general deconstruction of Y can be written as: where D is the number of a certain demographic unit and O D is economic output per that demographic unit.
A general form of the formula after the deconstruction of Y can be written as: Depending on the demographic unit chosen, it can be specified as: or The first one of these latter versions of the formula is basically identical with the classic, widely-used IPAT-formula (Chertow 2001

Deconstructing Z
Many authors identify Z with the T factor of the IPAT-formula. However, the ecological efficiency of economic output depends not only on the technologies used, but on two further factors, too.
First, also important is the structure (or composition) of the economy, that is the relative importance of the different sectors and industries. Obviously, this factor is partially overlapping with the technology factor, since the structure of the economy partly determines the technologies applied (and vice versa). However, it is also evident that regardless of the technologies used the transformation of the biosphere caused by certain industries will always be greater than that of others. (For example, it is almost certain that chemical industry will be less environmentally friendly than education.) Second, also relevant is the geographical pattern of the economy, that is, the extent of spatial separation between the economic subprocesses (e.g., between production and consumption). The more the economic subprocesses are separated in space, the greater the extent of transformation of the biosphere is (if the other factors on the right hand side remain unaltered). The explanation for this is at least threefold. First, because of geographical distance people, including economic decision-makers, have less experience on the environmental changes taking place during the economic cycle of a certain product (Princen 1997). Second, even if these environmental changes are known, the more distant they are, the less one cares about them generally. Third, since transport requires energy, more transport results in greater transformation of the biosphere (e.g., because more fossil fuels are combusted).
Accordingly, Z can be deconstructed as: Where T is the environmental impact of technologies, S is the structure of the economy and G is the geographical pattern of the economy. 4 To sum up, the most detailed version of the formula can be written as: Depending on the demographic unit chosen the following two versions can also be drawn up: The IPAT-formula (also frequently dubbed as model, identity or equation) was born in the early 1970s. It crystallized during the course of a fierce debate between three renowned environmental thinkers of that age: Paul Ehrlich and John Holdren on the one side and Barry Commoner on the other (e.g., Commoner 1971Commoner , 1972Holdren 1971, 1972). The essence of the IPAT-formula is that the extent of human impact on the environment is the direct function of the product of three factors, expressed as: I = PAT. Where I is the extent of human impact on the environment, P is population size (number), A is affluence per capita, and T is technology, that is how environmentally (un)friendly are the technologies used. For the sake of accuracy, all of the above factors (except P) are redefined here based mostly on Goodland & Daly (1996). To put it shortly, human transformation of the biosphere is a more precise term than human impact on the environment (see above); "affluence" would be an inaccurate and misleading term in this context, since as Harrison (1994) points out: it cloaks the fact that even subsistence levels of consumption have an environmental impact"; and the third factor on the right hand side should contain not only technologies (see below). There also exists a stochastic reformulation of the IPAT-formula called STIRPAT, which has been a valuable tool for the operationalization of the formula (Dietz & Rosa 1994;Dietz 2017). 4 In an earlier paper (Takács-Sánta, 2004) I identified the S and the G factors as important driving forces behind human transformation of the biosphere (but did not analyze them in detail). Ekins (1993) mentions in passing the first of these (though his wording is not entirely unequivocal) and later also Rosa & Dietz (2012) and Rosa et al (2015) emphasize its importance. However, building the second one in the formula was likely to be an absolutely new idea, at least I have not found any other work raising this issue before.

3
The factors on the right hand side of the latter two equations can be regarded as the direct driving forces behind human transformation of the biosphere. 5

Indirect driving forces
Factors lying behind the direct driving forces discussed above can be regarded as indirect driving forces of human transformation of the biosphere. These indirect forces can be divided into two groups: cultural and non-cultural factors. 6 Two subgroups of factors can be determined in both of these categories. The cultural subgroups are mind and social institutions. Mind refers not only to the cognitive layer (i.e., knowledge), but deeper layers as well, such as values and worldview. Social institutions are the constitutive elements of a society that are able to reproduce themselves and thus are typically trans-generational. Institutions can be typed as economic, political, legal, etc. (Miller 2019).
Cultural factors are constantly formed and preserved by people, groups of people and organizations as far as their respective power makes it possible. Accordingly, power is defined here as the ability to shape and control culture, that is social institutions and the mind of people.
The non-cultural subgroups contain biological and geographical factors (cf. Sack 1990). Biological factors refer to our "inner nature," that is mostly to genetics. Geographical factors are mainly physical geographical features, such as terrain features and climate. However, the spatial distribution of people (a social geographical, but basically biogeographical feature) is also important: it matters whether the same number of people are aggregated in a smaller space (i.e., cities) or distributed more evenly in space (i.e., countryside), as shown by examples below.

Behavior
The behavior of individuals, groups of people and organizations mediates between indirect and direct driving forces. This means that our behavior is shaped by our mind, social institutions, as well as biological and geographical factors. On the other hand, behavior directly affects population size (or the number of households), the economic output of the demographic unit chosen, the technologies used, and the structure and geographical pattern of the economy. 7

The model
Now our model is completed (Fig. 2). It shows us that indirect driving forces determine the way individuals, groups of people and organizations behave. Their behavior in turn affects the factors that determine the extent of human transformation of the biosphere (i.e., direct driving forces). These actors, in proportion to their respective power, can reshape (or preserve) the cultural driving forces as well. By the help of some simple examples, let's see how the model works.
In the first case the actor using power is a government that imposes a new tax (an element of an economic institution) on a particularly environmentally harmful industry, thus making this industry less profitable. Consequently, investors may turn to environmentally more benign industries reducing the extent of human transformation of the biosphere (B) due to the decrease in the formula's S factor.
In the second case the actor is a non-governmental organization targeting the mind of people by creating a powerful booklet about voluntary simplicity. Several readers will change their lifestyle (behavior) according to the booklet, hence the O P factor of the formula decreases, and so B, as well.
Generally, non-cultural factors cannot be shaped by the actors mentioned above, but nevertheless their behavior is affected by these factors. Our third case is that human sexual behavior is to a great extent determined by genes, and this behavior in turn affects the P factor of the formula. In the fourth case the flat terrain of a city makes the riding of bicycle a convenient behavior choice contributing to a low T factor of the formula (at least regarding mobility).
Finally, let us consider a quite rare case when a non-cultural factor is modified (indirectly) by a human actor. A government trying to foster urbanization can use propaganda to make city lifestyle more appealing (thus affecting the mind of people) or can help to create new jobs (elements of economic institutions) in cities and so attracting people there. The environmental impact of the resulting urbanization is controversial (Dietz et al. 2010;Rosa & Dietz 2012) since, for instance, it causes the increase in the formula's G factor (as long-distance transport is indispensable to satisfy the needs of a lot of people living in a densely populated area), but may decrease O H (since, for instance, the heating of attached flats is more energy-efficient than that of single houses).

Limitations and strengths of the model
On the one hand, every model is just a caricature of reality. On the other hand, a good model can help us to understand our world by focusing our attention on what is important and neglecting what is not so important.
There are at least four significant limitations of the present model. First, this is a static model lacking any dynamicsthough the rate of increase (or decrease) in human transformation of the biosphere is as important as its extent. 8 Second, it does not capture the various interactions between the direct driving forces (cf. Footnote 5). Third, indirect driving forces are not sophisticated, but just lumped together in broad categories (e.g., mind, social institutions) instead. Fourth, the model cannot help us neither quantifying our environmental impact, nor determining the relative roles of the various driving forces in it. Nevertheless, the model has its strengths, too. To my knowledge, this is the most detailed global, general model aiming to understand the causes of our ecological crisis so far. Compared to similar former models it identifies more direct driving forces; it not just distinguishes between direct and indirect driving forces, but also identifies non-cultural indirect driving forces beside cultural ones; and it finds the place of human behavior as a mediator between indirect and direct driving forces. Furthermore, the model may help us to identify the main strategies to resolve the ecological crisis.

The basic strategies of environmental sustainability
The simplest form of the formula shows us the two main strategies of environmental sustainability. The first one is the strategy of sufficiency, that is, the decrease in economic output (Y); and the other is the strategy of (eco-)efficiency, that is, the reduction in transformation of the biosphere per unit economic output (Z) (e.g., Sachs 1995).
The versions of the formula obtained as a result of the deconstruction of Y and Z show us that both strategies can be decomposed into sub-strategies. The sub-strategies of sufficiency are the reduction of the number of a demographic unit (D) (that is, the reduction of in population size or the number of households), and the reduction of economic output per a demographic unit (O D ). The sub-strategies of (eco-)efficiency are the use of environmentally friendly technologies (reduction of T), the shifting of the structure of the economy in an environmentally friendly direction (reduction of S), and the localization of the economy (reduction of G). 9 Finally, indirect driving forces show us that the realization of the above (sub-)strategies depends on cultural changes, that of mind and social institutions. 10 These cultural changes Fig. 2 A general, global model of the driving forces behind human transformation of the biosphere 8 It is mostly because the faster the rate of the increase is, the more difficult is the adaptation of humans and other living organisms. 9 In some cases, using one of these sub-strategies might jeopardize another sub-strategy. For instance, the localization of an economic activity might result in the increase in S, if that activity does not fit the local environment. An example is the desiccation of the Aral Sea, which was the result of (a not ecologically minded) localization: trade was eliminated by the cultivation of high-water-requirement crops in a semi-arid environment, the intensive irrigation in turn caused a regional ecological catastrophe (Micklin et al. 2014). 10 We can hardly change most non-cultural forces in preferred ways, and it might also be undesirable to try. may result in the pro-environmental behavior of individuals, groups of people and organizations, that is behavior causing the decrease in environmental impact (cf. Stern 2000) through the attenuation of the direct driving forces.
Will a new ecological culture ever be born globally? It depends on whether the actors desiring this change will have enough power, that is whether they will be able to reshape social institutions and the mind of people. Hence, the struggle for environmental sustainability is ultimately a struggle for power.
Funding Open access funding provided by Eötvös Loránd University.

Declarations
Conflict of interest There are no conflicts of interest.
Availability of data and material Not applicable.

Code availability Not applicable.
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http:// creat iveco mmons. org/ licen ses/ by/4. 0/.