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Degrowth and the Carbon Budget: Powerdown Strategies for Climate Stability - Part 1

Ed. note: This post is excerpted from a paper which can be accessed on the Simplicity Institute website here. We are publishing it on Resilience.org in two parts. Part 2 will be published later this week.

1. INTRODUCTION1 

In recent years the notion of a ‘carbon budget’ has entered the lexicon of climate science (e.g. IPCC, 2013; Meinshausen et al, 2009). This concept refers to the estimated maximum amount of carbon emissions that can be released into the atmosphere in order to retain a reasonable chance of keeping global temperature levels below a 2°C temperature rise above pre-industrial levels.  This is the global temperature threshold reaffirmed during the Copenhagen conference in 2009 but which many climate scientists argue should be revised downward (see, e.g., Jordan et al, 2013). Although the science underpinning the carbon budget is increasingly robust (see Le Quere et al, 2013), many scientists, politicians, and the broader public have been slow to recognise its radical socio-economic and political implications. 
 
In order to keep within a ‘safe’ temperature threshold, deep and rapid decarbonisation is required, and yet existing trends show that global emissions are still growing rapidly. According to the most recent IPPC report (2013), the world’s carbon budget could be entirely used up within 15-25 years, a scenario that would almost certainly lock the world into a future that is 2°C warmer, and more likely 4°C or 6°C degrees warmer (Christoff, 2013; Potsdam Institute, 2012). The consequences and risks of the current ‘business as usual’ scenario highlight the urgency with which deep decarbonisation must take place.

Given what is at stake here – the viability of the planet for human civilisation – carbon budget analyses need to become the basis for climate policies around the world, for they provide the most scientifically rigorous grounds for understanding the full extent of the climate challenge and what would constitute an appropriate response. The logic of the carbon budget numbers, however, leads to conclusions that most people, including most climate policy makers, refuse to accept, acknowledge, or understand. Most significantly, as outlined in this paper, the carbon budget arithmetic indicates that rapid decarbonisation may well be incompatible with continuation of current global economic growth trends and paradigms. In fact, even more challengingly, carbon budget analysis seems to imply that in the most highly developed regions of the world, keeping within the carbon budget will require ‘degrowth’ strategies of significantly reduced energy and resource consumption. This broad line of argument has been made often by degrowth scholars in recent years, but the latest carbon budget analyses are providing the degrowth position with compelling new scientific support.

Degrowth has been defined as ‘an equitable downscaling of production and consumption that increases human well-being and enhances ecological conditions’ (Schneider et al, 2010: 512). In a supplementary way, Serge Latouche (2014a: 211) has defined degrowth as 

"a societal project of transforming industrial and market societies into socially and ecologically sustainable societies of frugal abundance. Its principle aim is to dismantle a widely shared belief in the productivist model of development – that is, the ideology of unlimited economic growth – and to reconstruct industrial societies according to the ideal of ecological democracy."

By emphasising the need for contraction of the economy in the most developed nations, degrowth can be understood as a transitional phase that would ultimately stabilise in a steady-state economy that operates within the sustainable carrying capacity of the planet (see e.g. Daly and Farley, 2004). Within those ecological limits of significantly reduced energy and material throughput requirements, the art of living, of course, could forever improve and evolve.  

Like the notion of a steady-state economy, degrowth is not necessarily tied to notions of Gross Domestic Product (GDP) but is fundamentally a biophysical macroeconomic concept with profound socio-political implications, which leaves room for increased wellbeing even if GDP declines. Degrowth, therefore – which refers to planned economic contraction – must be distinguished from recession, which signifies unplanned economic contraction. From within a degrowth paradigm, there is no reason why planned reduction of energy and resource consumption cannot be associated with increased wellbeing, if the transition is negotiated wisely. This creates conceptual space for ‘economic degrowth’ to be contrasted with ‘uneconomic growth’ (see Alexander, 2012a; Kallis et al, 2012; Kubiszewski, et al. 2013), which is the space within which this paper is situated.

This paper begins by examining the key conclusions of the carbon budget research literature and unpacking some of the assumptions that frame the various decarbonisation scenarios. After doing so, the paper builds on the work of climate scientists, Kevin Anderson and Alice Bows, who have led the climate science analysis of the implications of carbon budgets on economic growth goals and polices. Although Anderson and Bows have been insightful enough to see (and brave enough to acknowledge) that meeting carbon budget targets implies a rapid shift to degrowth strategies, particularly in the most developed economies, they have not yet provided a detailed discussion of the ways in which degrowth strategies might be integrated with the broader decarbonisation policy agenda. In the final sections of this paper, therefore, an attempt is made to contribute to this discussion by outlining the main elements of an integrated socio-economic and political strategy consistent with keeping emissions within the confines of the carbon budget.


2. THE FOUNDATIONS OF CARBON BUDGET ANALYSIS

The primary cause of greenhouse gas (GHG) emissions – especially CO2 emissions – is burning fossil fuels. It is now scientifically accepted that when GHGs are released into the atmosphere they retain extra heat which has a warming effect on the planet (IPCC, 2013). This is the most important dynamic which explains climate change as it is unfolding today, although other factors are at play too, such as deforestation. It follows that as more GHGs are released into the atmosphere, more heat will be absorbed, leading to further rises in average global temperatures. As the scientific understanding of climatic systems has developed in recent decades, it has become possible to estimate with increasing confidence the climatic impacts of further GHG emissions. In other words, scientists are able to predict within a range of probabilities the likely temperature rise that would result from a certain amount of further GHG emissions. This is the foundation of ‘carbon budget’ analyses (see generally, Steffen and Hughes, 2013; Committee on Climate Change, 2013). 

The size of the carbon ‘budget’ depends on the parameters of the analysis. There are four main parameters that must be stipulated in order to arrive at a ‘carbon budget’: (1) the units of the analysis (i.e. what is being counted: just CO2? Or all GHGs?); (2) the timeframe that defines the contours of the budget (i.e. from what date do we start counting emissions and what date defines the end point of the budget?) (3) what is the threshold temperature rise that we are trying to avoid (e.g. 1°C, 1.5°C, 2°C, 4°C, etc.); and (4) what probability is considered acceptable for keeping to that temperature threshold (e.g. 50%, 80%, 95% chance of success, etc.). Once those parameters are defined, the foundations of a ‘carbon budget’ analysis are in place. (Note that the phrase ‘carbon budget’ is used for simplicity, but as stated above, some analyses are not limited solely to carbon dioxide emissions).  

Although the parameters stated above are the main ones that shape a carbon budget, there are others that must also be considered. For example, aerosols (such as sulphur dioxide) have a cooling effect on the planet, so higher levels of aerosols (which may be harmful in other ways) have the potential to offset some of the warming effects of GHG emissions. Similarly, more CO2 will be able to be burned if other GHG emissions are reduced faster than expected, so some informed assumptions have to be made about these relationships. Another unknown is the extent to which carbon sequestration techniques such as carbon capture and storage (CCS) will be able to reduce the level of emissions from burning fossil fuels entering the atmosphere. 

As well as these issues, there are also complex questions surrounding climate sensitivity, changes in land use, and carbon cycle feedbacks, about which assumptions also have to be made, such as the extent to which emissions from CO2 will be absorbed by the oceans or how long CO2 will remain in the atmosphere (see Carbon Tracker and Grantham Institute, 2013). All these dynamics can increase or decrease the carbon budget, depending on the assumptions made. 

Although increasing numbers of scientific articles and organisations have offered estimates of carbon budgets, the following review is limited, by way of example, to two of the most influential and frequently cited references. The first is the foundational publication by Meinshausen et al (2009). This paper provides a comprehensive probabilistic analysis ‘aimed at quantifying GHG emission budgets for the 2000-2050 period that would limit warming throughout the twenty-first century to below 2°C’ (Meinshausen et al, 2009: 1158). The authors conclude that limiting cumulative CO2 emissions over 2000-2050 to 1,000Gt of CO2 yields a 25% probability of warming exceeding 2°C, and a limit of 1,440Gt of CO2 yields a 50% probability. Between 2000-2006 global CO2 emissions were approximately 234Gt, which must be subtracted from those carbon budget estimates. Emissions since that time must also be subtracted. The authors note that keeping to these budgets would require leaving more than half of proven, economically recoverable fossil fuels in the ground (raising issues about ‘stranded assets’ to which I will return briefly later). If GHG emissions in 2020 are 25% above 2000 levels, then the analysis indicates that the probability of exceeding 2°C rises to 53-87%. We see here the types of frameworks and scenarios that can be discussed with the benefit of carbon budget analyses. It allows us to identify the level of emissions we are aiming to achieve at a particular time, and then back-cast scenarios in order to determine how to achieve the stated goal.    

The more recent Carbon Tracker and the Grantham Institute analysis (2013) is based on the same models as Meinshausen et al (2009) but explores some alternative assumptions. For example, this report assumes higher levels of aerosols in the atmosphere (which will offset some of the warming) and assumes greater reductions of non-CO2 GHGs (which allows for higher CO2 emissions but results in the same overall warming effect). Based on these alternative assumptions, the report then offers estimates of various carbon budgets for the period 2013-2049, with various temperature thresholds (1.5°, 2.5°, 3° and 4°) and two different probabilities (50% and 80%). The results are shown below in Figure 1.



Figure 1 – Carbon budgets for different temperature thresholds and probabilities (from Carbon Tracker and Grantham Institute, 2013: 10).

These two brief reviews of carbon budgets serve the purpose of outlining the nature of these analyses and their key conclusions. It is worth noting that this method of understanding the climate challenge has been given increased credibility in recent years with the IPCC (2013) and the International Energy Agency (2012a: 3)  both now drawing on carbon budget methodologies as central tools in target-setting and policy formulation. 


3. NORMATIVE ASPECTS OF CARBON BUDGET ANALYSIS

As noted above, setting different parameters to the analysis can produce higher or lower carbon budgets. The choice of different parameters, therefore, can have socio-economic and political implications, and this draws the scientific analyses into more normative, value-laden, or ‘politicized’ spaces. Indeed, even after a carbon budget has been determined, a critical normative question still remains about how that budget should be distributed between and within nations of the world, and what decarbonisation strategies should be adopted to keep emissions within the carbon budget. In the following sub-sections some of these normative questions are raised.       

3.1. Where should the temperature threshold be set? 

The temperature threshold is one of the most important questions to answer when framing a carbon budget analysis. The lower the threshold, the lower carbon budget. As climate science and climate politics have developed over recent decades, a maximum 2°C temperature rise above pre-industrial levels has become entrenched in the political discourse as representing a relatively ‘safe’ threshold, beyond which humanity would enter increasingly ‘dangerous’ territory. In recent years this threshold has been continuously reaffirmed in high-level climate negotiations, including at Copenhagen (2009) and Cancun (2010). Because of this, many carbon budget analyses are framed by a 2°C temperature threshold to reflect the international consensus, such that it is.2   

The 2°C threshold is of course a somewhat arbitrary threshold – why not 1.8°C or 2.2°C? It is an easily understood round number which may have served a useful political purpose when the framework for a global climate response was first being seriously negotiated in the mid-1990s. The most recent climate science evidence however suggests that i) many ecosystems are more sensitive to impacts at 2°C than was previously thought, and that ii) many risks are self-reinforcing, threatening to produce cascading environmental impacts that would roll on to affect social systems (see Jordan et al, 2013; Smith et al, 2009; Mann, 2009; Lenton et al, 2008). If current scientific knowledge was available in the mid-1990s, the threshold could well have been set at 1.5°C or below. 

While some climate scientists, policy makers and activists argue that revising the temperature downward is a crucial step towards ensuring an appropriate alignment between scientific and policy objectives, others continue to argue that revising the threshold downward might have a negative effect if such a goal was widely perceived to be unattainable (see Jordan et al, 2013). Whatever the case, if once it was thought that 2°C was the guard-rail keeping humanity ‘safe’, it may now be more accurate to say that it represents the bare minimum dividing line between ‘dangerous’ and ‘extremely dangerous’ climate change (Anderson, 2012; see also, Spratt, 2014a; Spratt, 2014b).         

3.2. What probability of success should be assumed?

Once a temperature threshold has been determined, a carbon budget must be framed in relation to a particular probability of success or failure. If climate systems were perfectly understood, this would be unnecessary, because scientists would be able to state with relative certainty that if x amount of CO2 were released into the atmosphere then this would produce a temperature increase of precisely y. Needless to say, the complexity and interrelationships of climatic systems defy perfect understanding, so temperature effects from emissions can only ever be stated in terms of probability. This raises the normative question of what probability of avoiding dangerous climate change our species considers justified. The higher the probability of success, the lower the carbon budget.

In trying to arrive at an ‘appropriate’ probability, we need to situate this debate in the context of what is at stake if we fail. Emissions are already having an effect on climatic and broader environmental systems, with glaciers and ice caps melting, coral reefs eroding, the boundaries for vector-borne diseases expanding, and the frequency of extreme weather events increasing (see generally, IPCC, 2014).  If these effects are occurring already, the question raised is: what effects will flow from a 2°C or 4°C or 6°C degree temperature rise? (see Potsdam, 2012; Christoff, 2013). When the consequences of a course of action are small, the risk of failing to avoid those consequences is less important. But when consequences are potentially extremely dangerous, even catastrophic, then it is rational to expect a substantially higher probability of success (see generally, Gardiner, 2011).
  
The language used in the dominant political discourse about climate policy targets is quite clear.  The Copenhagen Accord and Cancun Agreements both state categorically that the goal must be to ‘hold the increase in global average temperature below 2°C, and to take action to meet this objective consistent with science and on the basis of equity’ (UNFCCC, 2011). The European Commission (2007) is equally clear, affirming the need to ‘ensure that global average temperatures do not exceed preindustrial levels by more than 2°C’ and states that we ‘must adopt the necessary domestic measures’ to ensure this is the case (italics added). Similarly, the UK’s Low Carbon Transition Plan (DECC, 2009: 5) states ‘average global temperatures must rise no more than 2°C’ (italics added; see also, Anderson, 2012).

The language does not talk of ‘hoping’ to avoid dangerous climate change, or that we should ‘try’ to avoid it, and it does not suggest that we should aim for a 50:50 chance of avoiding dangerous climate chance. By using language such as ‘ensure’ and ‘must’ it can  be assumed that, when framing a carbon budget analysis, the probabilities of avoiding climate change should be very high – arguably in the range of 80-95%, or higher. Not only should this follow from the scientific literature considering the potentially dire consequences of climate instability, it also follows from one of the underlying principles of the environmental movement – the ‘precautionary principle’. In short, we should not gamble with the climate. This is especially so given that those who will be most affected by climate disorder (those in the poorest nations and future generations) have not been responsible for it. For these types of reasons, most carbon budget analyses have assumed a probability of success at 66% or higher, although other scenarios have explored probabilities of 50%. The choice of probability is a normative one that significantly influences any carbon budget analysis.  

3.3. How should the global carbon budget be distributed?  

Once a global carbon budget has been determined, there remains the critical question of how that budget should be distributed amongst (and within) nations. One seemingly objective and equitable way to distribute a carbon budget is to share it out equally on a per capita basis. While this approach has some intuitive plausibility, it ignores at least two critical issues. First, it ignores any ‘differentiated responsibility’ for the historic causes of climate change. A strong moral case can be made that those nations most responsible for historic emissions should bear the greatest responsibility for dealing with the effects of emissions, and if dealing with climate change implies hardship or burden, then again, those who caused the problem should shoulder that burden more than those least responsible. But even on this issue, we find the richest nations (which generally have the highest historic emissions) arguing that they should not be responsible for GHG emissions in historic eras when it was not understood that emissions warmed the planet. The date at which the science of climate change was sufficiently well established is a matter of some debate, although 1990 – the year the IPCC’s First Assessment Report was published – is one reasonable option.     

A second problem with sharing the carbon budget equally on a per capita basis flows from the fact that billions of people still live lives of material destitution. Cheap fossil fuels provide vast reserves of dense energy that could be directed toward eliminating such impoverishment. Given this humanitarian predicament – wanting to eliminate poverty but also wanting to minimise GHG emissions – a strong moral case can also be made that if the world is to continue burning fossil fuels for some time, the bulk of that fossil energy should be spent lifting the poorest people out of destitution rather than increasing the wealth of the most affluent societies. Part of the reasoning here is that energy consumption has diminishing marginal returns to wellbeing, which implies that increased energy consumption will produce more wellbeing in the poorest nations than in the richest nations (see Diffenbaugh, 2013).3 

For these reasons, it follows that the apparent ‘equity’ of sharing a global carbon budget out equally on a per capita basis is in fact far from equitable. Instead, an equitable distribution would have to allow for more emissions from the poorer nations and those least responsible for historic causes of climate change, thus constraining the permissible emissions from the richest nations that are most responsible from climate and most technologically and financially capable of dealing with the necessary societal transformation.

This general position, in fact, has been accepted in the international climate negotiations, which acknowledges the need for ‘differentiated responsibility’, even if the exact weighting of distribution remains highly contested. The Copenhagen Accord (UNFCCC, 2010) clearly distinguishes between Annex 1 nations (broadly the OECD nations) and non-Annex 1 nations (broadly the non-OECD nations), and calls for a response to climate change ‘consistent with science and on the basis of equity’ (italics added). More specifically, the Accord acknowledges that ‘the time frame for peaking will be longer in developing countries’ and, most significantly, that ‘social and economic development and poverty eradication are the first and overriding priorities of developing countries’.   


4. THE RADICAL IMPLICATIONS OF CARBON BUDGET ANALYSIS

Having outlined the foundations of carbon budget analysis along with key parameters in relation to temperature thresholds, probabilities of success, and distributional issues, we are now in a position to unpack some of the implications by considering in more detail what these numbers actually mean for emissions reduction policies and strategies. In doing so, I draw primarily on the work of climate scientists, Kevin Anderson and Alice Bows, who have published a number of  rigorous and influential  papers on the economic policy implications of carbon budget analysis (Anderson and Bows, 2008a; Anderson and Bows, 2011; Anderson, 2012; Anderson, 2013). Although their conclusions can be seen as confronting, they in fact argue their case based on robust premises which, in ways discussed below, are actually very conservative. The numbers, in short, speak for themselves, but many find the message confronting because the numbers show that keeping temperatures below 2°C will require  Annex 1 nations to immediately initiate deliberate and planned ‘degrowth’ strategies of reduced consumption and economic contraction. The controversy this evidence-based conclusion has provoked has prompted Anderson (2013) to note that their critics ‘don’t so much disagree with our conclusion, but rather they simply dislike it’. In this section their arguments are outlined and analysed.  

Anderson and Bows offer their analyses on the following explicit assumptions and parameters (see especially, Anderson and Bows, 2011; Anderson, 2013):

1. The world should aim to keep warming below 2°C. As discussed above, 2°C used to be considered the ‘safe’ threshold, but more recent evidence suggests that a 2°C rise would be ‘dangerous’, which is why increasing numbers of scientists are questioning the 2°C threshold and considering a reduced target of 1.5°C or less (see Jordan et al, 2013; Sprat, 2014a; Spratt, 2014b). By staying with the 2°C threshold, Anderson and Bows are being conservative in their assumptions and keeping in line with the agreed goal of mainstream international climate discourse. 

2. The probability of exceeding 2°C is set at 50%. Although Anderson and Bows offer various scenarios based on different probabilities of exceeding 2°C, for present purposes their argument which assumes a 50% probability of exceeding 2°C is being considered. As discussed above, given the grave consequences that are likely to flow from a 2°C temperature rise or more, a 50% probability of exceeding that threshold is an extremely conservative premise. Not only does the language of the international community reflect a far lower probability (arguably in the vicinity of 1-10%), the precautionary principle would imply that a 50% chance of failure is far too risky.   

3. Non-Annex 1 countries peak in emissions by 2025. In order to determine how much of the global carbon budget is left for Annex 1 nations, Anderson and Bows first determine how much of the carbon budget non-Annex 1 nations will need to minimally develop their economies on the basis of equity. In making this assessment, they make what they acknowledge are ‘extremely ambitious’ (Anderson, 2013) assumptions with respect to the anticipated emissions peak in non-Annex 1 countries and their post-peak decarbonisation trajectory (as outlined in Anderson and Bows, 2011; Anderson and Bows, 2008a). Specifically, they assume that the non-Annex 1 nations will peak in emissions by 2025 and thereafter reduce emissions at an unprecedented 7% p.a. Note, however, that these ‘extremely ambitious’ assumptions are, if anything, favourable to the Annex 1 nations, since they imply less of the carbon budget is used up by the non-Annex 1 nations, leaving as much as possible for the Annex 1 nations.4 

4. Annex 1 nations must reduce emissions by 8-10% p.a. The Annex 1 carbon budget is determined by subtracting the non-Annex 1 emissions from the global carbon budget. Based on the above assumptions (all of which can be understood to leave a favourable carbon budget for Annex 1 nations), it follows that keeping to the carbon budget requires Annex 1 nations to decarbonise their economies by 8-10% p.a. over coming decades. Even that conclusion can be considered understated, given that the scenario was formulated in 2011 (Anderson and Bows, 2011), and since then carbon emissions globally have continued to rise (and indeed, at an increased rate). Every year emissions increase (or do not meet the 8-10% decarbonisation requirement) the decarbonisation strategies required to keep to the carbon budget become more stringent.   

5. Emissions reductions of more than 3% or 4% p.a. are incompatible with a growing economy. Given that energy consumption and economic growth are intimately connected (Ayres and Warr, 2009), and that any significant transition to renewable and more efficient energy systems is going to take many years and probably decades to roll out (see Smil, 2014; Smil, 2010), it is widely accepted amongst orthodox economists that emissions reductions of more than 3% or 4% p.a. are incompatible with a growing economy. This view is supported by the pre-eminent climate change economist, Nicholas Stern (2006); the UK’s Committee on Climate Change; and, as Anderson (2013) notes, ‘virtually every 2°C emission scenario developed by “Integrated Assessment Modellers”’. Anderson (2013) also points out that ‘if reductions of 4% each year are to occur in an economy growing at 2% each year, then the carbon intensity of the economy must continually improve at around 6% year on year’. Despite considerable engagement with the literature, Anderson admits that he has found no examples of economists suggesting that prolonged emissions reductions of 3% or 4% or more are compatible with a growing economy. On the contrary, Stern observes that annual reductions greater than 1% have ‘been associated with economic recession or upheaval’ (Stern, 2006: 204). Indeed, one of the only examples of deep and prolonged emissions reductions is during the collapse of the Soviet Union, when emissions fell by approximately 5% p.a. for ten years (Anderson, 2012: 25). As the Russian economy stabilised, however, and once more began to grow, emissions again began to rise. All this firmly suggests that decarbonising an economy by 8-10% p.a. is not something that can be achieved while growing the economy in conventional GDP terms.   

Admittedly, this is a point that economists, including Stern, assert without a much elaboration. It is certainly a key issue that deserves more critical attention, and obviously planning for decarbonisation will involve different dynamics than decarbonisation through collapse or recession. All the same, the implicit reasoning seems relatively strong. Scaling up renewables takes many years, even decades, so does improving efficiency (Smil, 2010; Jackson, 2009). Even the theoretically ‘ideal’ scenarios for scaling up renewables and efficiency have to be placed in social and political context, where those ‘ideal’ scenarios will never be fully achieved. Therefore, one can conclude with some confidence that decarbonisation of 8-10% p.a. will never be achieved solely through a ‘supply side’ transition to renewables and more efficient production, especially in a growing economy. In order to achieve significant absolute reductions in emissions of 8-10%, the transition to renewables and more efficient processes must supplemented by planned ‘demand side’ reductions in energy consumption, and this energy descent requirement is what puts into question the continuation of economic growth (Ayres and Warr, 2009).

6. Therefore, the Annex 1 nations must initiate a ‘degrowth’ strategy. If the Annex 1 nations must reduce emissions by 8-10% p.a. over coming decades in order to keep within their carbon budget; and, if emissions reductions of more than 3% or 4% are incompatible with economic growth, it follows, as Anderson and Bows conclude, that ‘for a reasonable probability of avoiding the 2°C characterisation of dangerous climate change, the wealthier (Annex 1) nations need, temporarily, to adopt a degrowth strategy’ (see Anderson, 2013). Although they have not provided much detail on what they mean by ‘degrowth’, the clear implication is that it means giving up the conventional pursuit of economic growth and deliberately seeking an equitable reduction of energy and resource consumption as necessary to meet their 8%-10% decarbonisation requirements. While this ‘radical’ conclusion flows logically from the conservative assumptions outlined above, it is a conclusion that contradicts most other large scale decarbonisation proposals which almost always assume that maintaining a safe climate is consistent with continued economic growth in both developing and the developed nations. (see, e.g. Grantham, 2013; SDSN and IDDRI, 2014). 
 

Perhaps the most compelling aspect of the argument put forward by Anderson and Bows is the cautious and moderate way in which the underlying assumptions are framed.  Each of the premises could in fact be justifiably more challenging. For example, if the temperature threshold was set at 1.5°C not 2°C; or if the probability of avoiding that threshold was raised to 80% or 90% not 50%; or if less ambitious figures were given for peak emissions and decarbonisation rates for the non-Annex 1 nations; and especially if all of those assumptions were not so moderately stated, then the available carbon budget left for the Annex 1 nations would be hugely reduced. This would demand significantly higher decarbonisation rates for Annex 1 nations, perhaps in the vicinity of 15% or 20% p.a. Accordingly, even if critics take issue with specific assumptions (e.g. argue that the temperature threshold should be 2.5°C or that decarbonisation at 6% p.a. is compatible with growth), this would not effect the overall conclusion that keeping to the carbon budget requires degrowth in the Annex 1 nations. Nevertheless, as noted, even some of the most promising climate policy documents of recent times (e.g. SDSN and IDDRI, 2014; Grantham Institute, 2013) steadfastly refuse to accept that an adequate response to climate might require rethinking the growth paradigm.5  

While critics will doubtless continue to object to degrowth strategies on the basis of a range of other arguments (including both socio-economic outcomes and political efficacy), when the above figures of the carbon budget are taken seriously, the case for some form of degrowth strategy is extremely strong on scientific grounds. In this sense the onus is on critics of the Anderson and Bows proposition to demonstrate any fundamental flaws in the key assumptions or logic of the argument. In fact, critics really need to respond to the degrowth argument based on more challenging premises and even higher decarbonisation requirements, given that the argument from Anderson and Bows is really too moderately stated (e.g. the probability of success should be far higher than 50%).   

It should be noted also that although this argument for degrowth is based solely on carbon budget analysis, it finds much support in more general ‘limits to growth’ literature (see generally, Meadows et al, 2004; Rockstrom et al, 2009; Trainer, 2010; Turner, 2012; Hopkins and Miller, 2012; Alexander, 2014a) and, more specifically, the emerging degrowth literature (see Latouche, 2009; Latouche, 2014b; Kallis, 2011; Alexander, 2012a; Victor, 2012). These literatures argue that the developed nations (in particular) must give up the growth paradigm for various ecological and social reasons, of which climate change is only one. 
     
Endnotes

1. The author would like to thank John Wiseman, Brett Paris, and David Spratt for very helpful feedback on an earlier version of this paper. It should not be assumed that these reviewers agree with all aspects of the following analysis.

2. It should be noted that 2°C is not accepted as a safe threshold by many of the least developed countries or the Association of Small Island States who, at Copenhagen and elsewhere, have been pushing for reduced thresholds. See also, Spratt, 2014a; Spratt, 2014b).

3. However, as discussed briefly later in the paper, it is critical that the carbon budget spent in the poorest nations, with the intent of lifting those nations out of poverty, avoids creating infrastructure that essentially locks them into decades of high-carbon living.

4. The other reason this premise can be considered ‘favourable’ to the Annex 1 nations is because the calculations are based on ‘production-based’ accounting not ‘consumption-based’ accounting. Given that many of the emissions in the non-Annex 1 nations are used up producing things which are ultimately consumed in the Annex 1 nations, a ‘consumption-based’ accounting of emissions would leave less of the carbon budget for the Annex 1 nations.

5. Two other potential responses to the argument that some form of degrowth is necessary to achieve key carbon budget targets are to point to the contribution which ‘carbon capture and storage’ (CCS) and geo-engineering could make to addressing climate change risks. While a full review of the rapidly expanding literature on both these options is beyond the scope of this paper, I do note the extensive range of serious ethical, governance and technical questions which have been raised about geo-engineering (see, e.g., Hamilton, 2013). As for CCS, this, indeed, may need to play a role in reducing emissions, but the technology at present is highly undeveloped, especially in the context of a decarbonisation requirement of 8-10% p.a. that must start immediately. Even when, or if, it becomes ready, implementation will take many years, probably decades, so it is not something that affects the necessity for exploring and implementing more immediate decarbonisation strategies.

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