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Beyond 'dangerous' climate change: emission scenarios for a new world
Kevin Anderson and Alice Bows Phil. Trans. R. Soc. A 2011 369, 20-44 doi: 10.1098/rsta.2010.0290

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Phil. Trans. R. Soc. A (2011) 369, 20–44 doi:10.1098/rsta.2010.0290

Beyond ‘dangerous’ climate change: emission scenarios for a new world
BY KEVIN ANDERSON1,3
1 Tyndall

AND

ALICE BOWS2, *

Centre for Climate Change Research, School of Mechanical, Aerospace and Civil Engineering, and 2 Sustainable Consumption Institute, School of Earth, Atmospheric and Environmental Sciences, University of Manchester, PO Box 88, Manchester M60 1QD, UK 3 School of Environmental Sciences and School of Development, University of East Anglia, Norwich NR4 7JT, UK
The Copenhagen Accord reiterates the international community’s commitment to ‘hold the increase in global temperature below 2 degrees Celsius’. Yet its preferred focus on global emission peak dates and longer-term reduction targets, without recourse to cumulative emission budgets, belies seriously the scale and scope of mitigation necessary to meet such a commitment. Moreover, the pivotal importance of emissions from nonAnnex 1 nations in shaping available space for Annex 1 emission pathways received, and continues to receive, little attention. Building on previous studies, this paper uses a cumulative emissions framing, broken down to Annex 1 and non-Annex 1 nations, to understand the implications of rapid emission growth in nations such as China and India, for mitigation rates elsewhere. The analysis suggests that despite high-level statements to the contrary, there is now little to no chance of maintaining the global mean surface temperature at or below 2◦ C. Moreover, the impacts associated with 2◦ C have been revised upwards, sufficiently so that 2◦ C now more appropriately represents the threshold between ‘dangerous’ and ‘extremely dangerous’ climate change. Ultimately, the science of climate change allied with the emission scenarios for Annex 1 and non-Annex 1 nations suggests a radically different framing of the mitigation and adaptation challenge from that accompanying many other analyses, particularly those directly informing policy.
Keywords: emission scenarios; Annex 1; non-Annex 1; cumulative emissions; climate policy; emission pathways

1. Introduction
The 2009 Copenhagen Accord [1] has received widespread criticism for not including any binding emission targets. Nevertheless, it does reiterate the international community’s commitment to ‘hold the increase in global temperature below 2 degrees Celsius, and take action to meet this objective
*Author for correspondence (alice.bows@manchester.ac.uk). Electronic supplementary material is available at http://dx.doi.org/10.1098/rsta.2010.0290 or via http://rsta.royalsocietypublishing.org. One contribution of 13 to a Theme Issue ‘Four degrees and beyond: the potential for a global temperature increase of four degrees and its implications’.

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While the inclusion of nearer-term targets is certainly a welcome complement to targets for 2050.royalsocietypublishing. Building particularly on previous analyses by Anderson & Bows [2] and more recently by Macintosh [3]. though this is not made clear in the Accord. it is assumed that the ‘2 degrees Celsius’ relates to the temperature rise above pre-industrial levels. Alongside these global analyses a growing range of ever more detailed national-level energy and emission scenarios are being developed (e. 2010 Beyond dangerous climate change 21 consistent with science and on the basis of equity’ [1].g.g. Total cumulative emissions produced by nations that underwent industrialization in the nineteenth century and first half of the twentieth century will be eclipsed if the five billion people currently resident in non-Annex 1 nations remain or become locked into a fossil fuel economy. as it stands. Trans. the paper translates earlier global assessments of cumulative emissions into emission pathways for Annex 1 and non-Annex 1 nations. However. Phil.5]). . preferring instead to focus on the ‘peaking of global and national emissions as soon as possible’ and the need for ‘Annex I Parties to implement .org on December 27.6–10]). each with a differing quantity of cumulative emission over the twenty-first century and hence with different temperature implications (e. A (2011) . Clearly. Recent years have seen the development of an increasing number of global emissions scenarios. this dramatic potential for emissions growth within non-Annex 1 nations is typically neglected in global and national mitigation scenarios.g. . Specifically. By considering global emission budgets alongside emission pathways for non-Annex 1 nations. Moreover. Although included in non-mitigation energy scenarios (e. quantified economy-wide emissions targets for 2020’. quantify the degree of mitigation required to meet this commitment nor does it give an indication of whether it is still possible to do so. electricity and transport within Annex 1 nations coupled with the very rapid industrialization of many non-Annex 1 nations. Analysis framing The first decade of the new millennium has witnessed unprecedented increases in emissions reflecting ongoing high levels of energy usage for heat. the Accord recognizes ‘that the time frame for peaking will be longer in developing countries’ and also. the Accord makes no mention of cumulative emissions as providing the scientifically credible framing of mitigation. however. such integration is rare with 1 For the purpose of this paper. this paper illustrates the increasing relevance of the latter for the mitigation policies of Annex 1 nations. and despite making reference to being guided by the ‘science’. R. very significantly. Soc. [11–13]). the Accord still falls short of acknowledging what the science makes absolutely clear—it is cumulative emissions that matter. The importance of the distinction between Annex 1 and non-Annex 1 is also noted in the Accord. in particular China and India. [2. that ‘social and economic development and poverty eradication are the first and overriding priorities of developing countries’. integrating national and global analyses is a prerequisite of understanding the scale and rate of mitigation. This paper takes both the Accord’s commitment to ‘hold the increase in global temperature below 2 degrees Celsius’ along with its focus on the nearer term targets. and considers these in light of post-2000 and recession-adjusted emission trends.1 The Accord does not. [4.Downloaded from rsta. impacts and adaptation associated with differing levels of climate change. 2.3.

2 Such analysis cannot substitute for detailed national-level assessments. China) and regions such as sub-Saharan Africa. Anderson and A. Without such quantification it is not possible to derive the accompanying range of twenty-first century cumulative emissions budgets from which emission pathways can be derived. at least a very low one [16]. However. to ensure that global average temperature increases do not exceed preindustrial levels by more than 2◦ C’ [15] (emphasis added).royalsocietypublishing.3 The paper comprises three principal analyses. but does offer clear guidance as to the scale and rate of mitigation necessary to avoid particular rises in temperature above pre-industrial levels. whilst China’s total emissions are now higher than those from any other nation.org on December 27. Phil. The previous Secretary of State for Energy and Climate Change. . below 2 degrees Celsius’ reflects the clear and long-established stances of both the European Union (EU) Commission and the UK Government. hence. In the absence of such quantification. Ed Miliband. probabilities may be inferred based on the approach developed for the Intergovernmental Panel on Climate Change’s (IPCC’s) reports. the language of many Government statements suggests. The EU maintains it ‘must adopt the necessary domestic measures .Downloaded from rsta. this paper provides an improved and more contextual understanding of the extent of the mitigation challenge specifically and the adaptation challenge more generally. EU’s and UK Government’s 2 Similar but less-contextual analyses also illustrate the division of global emissions between Annex 1 3 It and non-Annex 1 nations (e. the UK Government published its UK Low Carbon Transition Plan. . the Accord. temperature. . EU and the UK do not make explicit what quantitative ‘risk’ of exceeding 2◦ C is considered ‘acceptable’. 5] (emphasis added). (a) Determining the ‘appropriate’ probability for 2◦ C The framing of the Copenhagen Accord around the importance of ‘hold[ing] to . Following this approach. Although this language is qualitatively clear. is important to note that within non-Annex 1 nations there will be significant differences in peaking years and emission reduction rates between the rapidly industrializing nations (e. in which it stated explicitly that ‘to avoid the most dangerous impacts of climate change. their per capita emissions are around one fifth of those for the USA. [14]). For example. A (2011) . are unlikely to succeed those in the USA in the next two to three decades (see note 17 for a discussion on cumulative per capita emissions). stating ‘we should limit climate change to a maximum of two degrees’ [18] (emphasis added). The second explores the implications of incorporating all greenhouse gases within the scenario pathways for a similar chance of exceeding 2◦ C. Trans. subsequently reiterated this commitment. if not a zero probability of exceeding 2◦ C. By disaggregating selected global emission pathways into Annex 1 and non-Annex 1 nations. R. Within the UK. Bows little more than perfunctory correlation between national and global emission pathways. 2010 22 K. 23]. in July 2009.g. and given current trends and agreements. The third considers how a slower uptake of mitigation measures combined with later emissions peaking impact on cumulative emissions and. . Soc. the Accord’s.g. The first derives pathways for CO2 emissions consistent with reasonable-to-low probabilities of exceeding 2◦ C. p. p. average global temperatures must rise no more than 2◦ C’ [17. whereby a correlation is made between the language of likelihood and quantified probabilities [19.

where the relevant policy community (and recent legislation) align themselves closely with the science of climate change.6 In part this reflects the continued dominance of ‘end point’ targets7 rather than scientifically credible cumulative emission budgets and their accompanying emission pathways. R. the ‘less likely’ end of the spectrum. and wider public and private decision making in both bringing about the scale of mitigation accompanying 2◦ C and responding to the impacts and associated adaptation of a failure to significantly mitigate. Trans. at least collectively. albeit with the important caveat that other nations. at their highest 5–33% of exceeding 2◦ C). more recently. the report proceeds to describe an emissions pathway out to 2050. 8 The 63 per cent probability of exceeding 2◦ C is an outcome of the CCC’s modelling approach and relates to its global cumulative emissions budget.org on December 27. these have since been re-evaluated with the latest assessments suggesting a significant increase in the severity of some impacts for a 2◦ C temperature rise (e. Given the UK budget is premised on the CCC’s choice of regime for apportioning global emissions between nations. The first report of the UK’s Committee for Climate Change (CCC) [8] heralded a significant departure from a focus on end-point and typically long-term targets. the IPCC categorizes a 33 per cent probability of missing or exceeding something as ‘unlikely’. acknowledging explicitly the need to re-align policy with cumulative emissions rather than simplistic targets. 10 per cent as ‘very unlikely’. the disjuncture remains. [20. However. but between dangerous and ‘extremely dangerous’ climate change. 6 Although this paper explicitly steers away from issues of governance. 7 Typically 2050 but also. Although the language of many high-level statements on climate change supports unequivocally the importance of not exceeding 2◦ C. there are clearly major implications for all tiers of government.g. Phil. although the UK Government’s framing of its climate change legislation is the first to detail emission pathways. Nevertheless. in which case the importance of low probabilities of exceeding 2◦ C increases substantially. it is reasonable to describe the UK’s budget as correlating with a 63 per cent chance of exceeding 2◦ C. A (2011) 4 At . and even a highly conservative judgement would suggest the statements represent no more than a 5–33% chance of exceeding 2◦ C. 21]. ceteris paribus.4 If government responses to climate change are to be evidence-based or at least informed significantly by science. not between acceptable and dangerous climate change. The characterization of 2◦ C5 as the appropriate threshold between acceptable and ‘dangerous’ climate change is premised on an earlier assessment of the scope and scale of the accompanying impacts. the argument for low probabilities is reinforced still further. the accompanying policies or absence of policies demonstrate a pivotal disjuncture between high level aspirations and the policy reality. Complementing the UK’s 2050 emission-reduction target with short-term budgets. As it stands the carbon budget and emission pathway now enshrined in legislation are underpinned by analysis assuming a 63 per cent probability of exceeding 2◦ C [8.royalsocietypublishing.e. 5 per cent as ‘extremely unlikely’ and 1 per cent as ‘exceptionally unlikely’. However.Downloaded from rsta. even within nations such as the UK. 5 Or at least the rate of increase associated with a 2◦ C rise by 2100.8 a position that cannot be reconciled with the probabilities implied repeatedly by Government statements (i. p. Soc. 2020. that 2◦ C now represents a threshold. 2010 Beyond dangerous climate change 23 statements all clearly imply very low probabilities of exceeding 2◦ C. it is reasonable to assume.21]). it is still far removed from its and others’ high-level commitments to ‘limit climate change to a maximum of two degrees’ [18]. do not exceed their apportioned emissions budgets. Consequently.

within the non-Annex 1 nations. infrastructures.g. exploring consistency. but rather are premised on a cumulative emissions framing of climate change for which richer and more qualitative scenarios could be developed in terms of mitigation. 2010 24 K.royalsocietypublishing. This is certainly important for the transition of Annex 1’s existing built environment and infrastructures. it is appreciably more important for the development of new built environments. 16]. nuclear power. In general there remains a common view that underperformance in relation to emissions now can be compensated with increased emission reductions in the future. Bows While the climate specialists within the CCC are aware of the implications of their analysis and conclude explicitly that ‘it is not now possible to ensure with high likelihood that a temperature rise of more than 2◦ C is avoided’ [8. the framing of much of the detailed research and practice around adaptation. The scenario pathways developed in this paper are explicitly ‘backcasting’ and quantitative. 10 Such geographical vulnerability will need to be considered alongside other cultural. the relative simplicity of the analysis presented here permits the connection between temperature targets and emission reductions to be readily assessed. impacts and adaptation. p. carbon capture and storage. as the impacts of rising temperatures are unlikely to be linear and also given rising temperatures are increasingly likely to be accompanied by additional feedbacks and hence further temperature rises. Yet. institutional and economic factors if resilience to the impacts of climate change is to be embedded in development. the scenarios are internally consistent. Anderson and A. assessing plausibility and providing policy guidance [23]. adaptation must consider more extreme climate change futures than those associated with 2◦ C [22]. the language of many policy statements suggests such implications are not either understood or accepted.Downloaded from rsta. the gap between the scientific and policy understanding of the challenge needs urgently to be addressed. This 9 This is particularly evident in the continued recourse to the implementation of future and innovative low-carbon technologies (e.10 3. Soc. However. R.org on December 27. They are not vision-based. With regard to exploring the consistency of scenarios. From a mitigation perspective. These approaches vary in terms of ‘backcasting’ and ‘forecasting’. in relation to climate change it suggests the scale of current emissions and their relationship to the cumulative nature of the issue is not adequately understood. Scenario pathway assumptions Scenario approaches are increasingly used within mitigation and adaptation research for visioning alternative futures. agricultural practices and water regimes etc. Trans. As it stands and in keeping with the dominant policy discourse. A (2011) . where an opportunity still exists for societies to locate in areas geographically less vulnerable to the impacts of climate change. In that sense. etc. is informed primarily by the 2◦ C characterization of dangerous climate change.9 Although for some environmental concerns delaying action may be a legitimate policy response.) as the principal route by which emissions reductions will be achieved. Phil. What is perhaps less evident is the implication of this gap for adaptation. and range from top-down and quantitative through to more bottom-up and qualitative assessments. marine-based biofuels. if guided quantitatively at all. a position that cannot be reconciled with the rate of reductions implied in high-level statements on 2◦ C.

org on December 27. Soc. building particularly on the work of Macintosh [3] and Anderson & Bows [2.11 (a) Cumulative emission budget The scenario pathways developed in this paper illustrate quantitatively the scale of mitigation implied in high-level policy statements on 2◦ C. are more robustly incorporated than is possible through the coarser regimes reliant on global warming potential. how drought conditions may impact energy use for desalination and grey-water recycling or the impacts of changing precipitation and temperature on biomass yields. Moreover. but a recognition that the range of impacts associated with different levels of climate change and differential impacts on temperature and precipitation make bottom-up analysis much more challenging. Trans. if not all. the cumulative budget for CO2 -only is lower than would be the equivalent CO2 e greenhouse gas value. The advantage of this regime is that nonCO2 emissions. The scenario pathways are all premised on a cumulative emission budget approach. with regard to achieving consistency. A (2011) . Given there are merits and drawbacks for each of the budgetary regimes.25. and with direct reference to Annex 1 and non-Annex 1 nations. 2010 Beyond dangerous climate change 25 contrasts with most. for example. for a given temperature and assuming other factors remain unchanged.royalsocietypublishing. Macintosh’s high budget is excluded from the analysis. The CO2 -only budgets considered in this paper are the same as the middle and lower estimates used by Macintosh [3]. This is not a criticism of existing bottom-up analyses. Phil. both are considered in this paper. the potential of culturally distinct migrants to embed alternative practices into established transport and housing energy use. The budgetary regime used by Macintosh [3] separates CO2 emissions from non-CO2 greenhouse gases and aerosols by applying Meinshausen et al.’s [7] assumptions on the net radiative forcing of the non-CO2 components. the approach poorly represents the contextual framing of emission scenarios. R. including aerosols. the link between aerosol emissions and assumptions about fossil fuel combustion and rates of deforestation. 11 For (i) The CO2 -plus regime (C +) and twenty-first century budgets example. However. However. bottom-up mitigation analyses where consistency is constrained to issues of mitigation with climate related impacts typically exogenous to the analyses. given the analysis here illustrates pathways offering an ‘unlikely to extremely unlikely’4 chance of exceeding 2◦ C. although offering significant scientific merit. if not impossible.26]. few if any energy scenarios addressing mitigation include reductions in efficiency of thermal power stations if the temperature of cooling water rises. While Macintosh [3] focused on CO2 -only emissions in correlating twentyfirst century budgets with global mean temperatures (denoted by the CO2 plus regime).Downloaded from rsta. Macintosh also analysed a higher budget of 2055 GtCO2 (560 GtC) as an ‘outer marker’ of abatement necessary for avoiding a 2◦ C. the budgets within Anderson & Bows’ analysis were for the basket of six Kyoto gases. Consequently.24] but also on a range of wider studies [7. the scenario pathways demonstrate the disjuncture between such high-level statements and the emission pathways proposed by many policy-advisers and academics.

Bows The two remaining budgets. 13 Probabilities based on Meinshausen et al.’s PRIMAP tool [28] does not permit a direct calculation of the probability of exceeding 2◦ C for emission pathways that maintain a substantial and long-term emission burden. Soc. R. Consequently. according to Macintosh reflects the ‘risk that climate-carbon cycle feedbacks respond earlier and more strongly than previously believed’ and corresponds with a higher probability of not exceeding 2◦ C. Evidently. The two CO2 e budgets within this paper are those used within Anderson & Bows [2] and represent the low (1376 GtCO2 e) and high (2202 GtCO2 e) ends of the IPCC AR4 cumulative emission range for stabilization at 450 ppmv CO2 e [29]. it assumes the ‘CO2 equivalence’ of Kyoto gases reasonably captures the warming implications of non-CO2 emissions from producing food for an increasing and more affluent population. The latter.’s PRIMAP tool for estimating probabilities of exceeding 2◦ C [28]. These emissions are typically related to agriculture and food production. Phil. 15 Refers to the lowest level of annual emissions considered viable in the scenario. The first is informed by the Garnaut Climate Change Review’s 450 ppm CO2 e stabilization scenario [27]12 and according to Macintosh [3] provides an approximate 50 per cent chance of not exceeding 2◦ C. 14 ‘Twenty-first century low-emission’ scenarios are premised on low fossil fuel combustion and low deforestation rates. Trans.royalsocietypublishing. it is necessary to use up-to-date and complete emissions data to construct future emission pathways. (b) Empirical data The continued and high level of current emissions is consuming the twentyfirst century emission budget at a rapid rate. a coarse-level but nevertheless adequate estimate is possible if the long lived gases within the ‘emissions floor’15 are added to the 2000–2050 cumulative values.Downloaded from rsta. In relation to aerosols it assumes they are both short-lived and sufficiently highly correlated with fossil fuel combustion and deforestation as to have little net impact on temperatures associated with twenty-first century lowemission scenario pathways [10].13 (ii) The basket of six regime (B6) and twenty-first century budgets The B6 regime. 12 For more details see Macintosh [3]. Anderson and A. 1578 GtCO2 (430 GtC) and 1321 GtCO2 (360 GtC). but it more appropriately captures the contextual implications of alternative emission scenario pathways. The probabilities related to 2◦ C in the B6 regime do however take into account the radiative forcing of the different emissions including aerosols based on assumptions embedded in Meinshausen’s et al. Within this paper data are aggregated for the latest year available from a number of different sources. A (2011) . are taken directly from Macintosh [3]. 2010 26 K. Currently Meinshausen’s et al. used previously by Anderson & Bows [2].14 Moreover. assumes the correlation between global mean temperature and cumulative emissions of the basket of six Kyoto gases as adequate for informing policy-makers of the scale of mitigation necessary.’s [7] model assumptions can be calculated using the PRIMAP tool [28] if the 2000–2049 emissions are known.org on December 27. However. the CO2 e regime is not as scientifically robust as the CO2 -only regime.

data are taken for each Annex 1 and non-Annex 1 nation from the Global Carbon Project using the Carbon Dioxide Information Analysis Centre (CDIAC) [30] and aggregated to produce an Annex 1 and non-Annex 1 total.39]. a recent study by the International Maritime Organisation [37] has produced a time series for greenhouse gas emissions associated with international shipping activity.Downloaded from rsta. However. The 2006–2008 emissions are derived from estimates of fire emissions using satellite data from the Oak Ridge National Laboratory Distributed Active Archive Center Global Fire Emissions Database in combination with a biogeochemical model [43]. This crude method of apportionment was used previously (e. though inevitably coarse-level. 2010 Beyond dangerous climate change 27 (i) Energy and industrial process emissions For energy and process related CO2 emissions from 2000 until 2008. Their figures are estimated based on deforestation statistics published by the United Nations Food and Agriculture Organization [42] and a bookkeeping method up until 2005. and given difficulties in apportioning international shipping emissions to nations [38. Trans. To estimate the proportion of international shipping CO2 emissions split between Annex 1 and non-Annex 1 nations. division of emissions between Annex 1 and non-Annex 1 nations. Non-Annex 1 international aviation CO2 data are taken from the International Energy Agency [33] as non-Annex 1 nations do not submit this information to the UNFCCC. The nationally constructed data from this source exclude CO2 emissions from international aviation and shipping. However. A (2011) .royalsocietypublishing. [36]). Instead. To include these additional emissions. 16 A hybrid approach for apportioning aviation emissions between regions may provide insights into potential apportionment regimes for shipping [40]. international aviation CO2 for Annex 1 nations is taken from the memo submissions to the United Nations Framework Convention on Climate Change (UNFCCC) [32]. data are taken from an interpolation between the 2005 and 2010 EPA projections. These data provide a figure for the global aggregated CO2 and other greenhouse gas emissions between 1990 and 2007. the data have previously been subject to high levels of uncertainty [34–36]. the data are not disaggregated into national statistics. For international marine bunkers. R. Soc.16 (ii) Deforestation and land-use change For deforestation and land-use change (hereafter referred to as ‘deforestation’) data between 2000 and 2008 carbon emissions are again taken from the Global Carbon Project Carbon Budget Update 2009 [41]. Phil. is also used here as an adequate.org on December 27. (iii) Non-CO2 greenhouse gas data The non-CO2 greenhouse gas emission data for 2000–2005 are based on the US Environmental Protection Agency (EPA) estimates [44]. data are not taken from CDIAC as their bunker fuel CO2 emission data are not disaggregated between nations and global marine bunker emissions are based on sales records that currently underestimate significantly the global greenhouse gas emission burden [31]. an assumption is taken that shipping activity is directly proportional to each nation’s proportion of global GDP.g. For 2006 and 2007.

Trans. Although the crisis is beginning to show within 2008 emissions inventories. Soc. R. the same percentage growth rates for national emission trends are applied as for Annex 1 and non-Annex 1 domestic CO2 emissions between 2008 and 2010. Non-Annex 1 nation aviation bunkers are assumed to be stable at 2007 levels until 2009. do not exceed the global ‘2◦ C’ cumulative budget.5 per cent in 2010. However. In the absence of such data. Annex 1 and non-Annex 1 non-CO2 greenhouse gas emissions are assumed to proportionally follow the percentage change in their CO2 counterparts.Downloaded from rsta. the 2010 growth figure is assumed to be half the recent decade’s average (i. Phil. then the rate of growth for non-CO2 greenhouse gas emissions is also assumed to halve. — Decide on a global cumulative CO2 and greenhouse gas emission budget associated with a range of probabilities of exceeding 2◦ C. 2010 28 K. but given China is already reporting high levels of growth for early 2010.e.org on December 27.royalsocietypublishing. 2. estimates draw on the work of Macintosh [3] and the Global Carbon Project [41]. A (2011) . after which they grow at 2 per cent in 2010. Given the absence of recent data from the EPA. (c) Economic downturn The economic downturn of 2007–2009 had a direct impact on greenhouse gas emission growth rates. when added to non-Annex 1 and deforestation emissions.5 per cent decline in emissions in 2009. it is estimated Annex 1 nations’ emissions declined by 2 per cent in 2008.0 per cent in 2009 rising to 1. Scenario pathway development Following a brief explanation of how historical and deforestation emissions are accounted for. the construction of the scenario pathways involves the following steps. remaining static in 2009 and 2010. again half the recent decade’s average. Bows This dataset is identical to the one used within Anderson & Bows [2] but in this case individual national statistics are aggregated to produce the Annex 1 and non-Annex 1 totals. if the rate of growth halves for Annex 1 CO2 emissions. data were not available for either 2008–2010 bunker fuel emissions or 2009–2010 domestic fossil fuel CO2 emissions. Consequently. For international aviation bunkers. particularly those associated with energy. growth in global fossil fuel CO2 (excluding bunkers) is assumed to be −3. Anderson and A. fossil fuel CO2 (excluding bunkers) is assumed to decline by 6 per cent in 2009. Given the international marine bunker figures are based on proportions of global GDP. In other words.7%). it is assumed that their growth is also impacted by the economic downturn. 4. Non-Annex 1 nations are assumed to exhibit 0. non-CO2 greenhouse gas emission growth rates are typically lower than those for global fossil fuel CO2 by approximately 1–2% per year. — Construct emission pathways for the Annex 1 nations for which the cumulative emissions. For the emissions of non-CO2 greenhouse gases. stabilizing at 0 per cent in 2010. For Annex 1 nations. — Construct emission pathways for the non-Annex 1 nations with varying peak dates.

A (2011) 17 Factoring . 19 It is worth noting that a recent paper [45] based on analysis undertaken at Tsinghua University in Beijing makes the case that ‘reasonable rights and interests should be strived for. 2010 Beyond dangerous climate change 29 — Construct emission pathways for the non-Annex 1 nations with a 2030 peak date and more ‘orthodox’ annual reduction rates following the peak.royalsocietypublishing. However. only data for fossil fuel combustion. — Assess the potential future climate impact of these more ‘politically acceptable’ and ‘economic feasible’ pathways.17 Getting an appropriate balance of responsibilities is a matter of judgement that inevitably will not satisfy all stakeholders and certainly will be open to challenge.19 (b) Deforestation emissions To explore the constraints on emissions from Annex 1 nations of continued growth in emissions from non-Annex 1 nations. R. Given temperature correlates with cumulative emissions of greenhouse gases. the highly constrained emission-space now remaining for a 2–3◦ C rise in global mean surface temperature leaves little option but to explicitly neglect the responsibility of historical emissions in developing pragmatic twenty-first century emission profiles.18 is a pragmatic decision that. Whilst such an outcome may have some moral legitimacy. Trans. (a) Historical emissions In developing emission pathways for Annex 1 and non-Annex 1 regions it is necessary to make explicit which region is deemed responsible for which emissions. However. the approach adopted for this paper in which historical (and deforestation) emissions are taken to be global overheads. it is important to reflect briefly on the treatment of recent historical emissions. based on the equity principle. 18 Emissions not attributable to any specific geographical location. industrial processes and agriculture are split between Annex 1 and non-Annex 1. — Construct emission pathways for the Annex 1 nations with a 2015 peak date and ‘orthodox’ annual emission-reduction rates following the peak. the authors demonstrate how China’s historical cumulative emissions are only one-tenth of the average in industrial countries and one-twentieth that of the USA. reflected through cumulative emissions per capita’. Such an approach could be argued to unreasonably favour non-Annex 1 nations as deforestation emissions occur within their geographical boundaries. Soc. Deforestation emissions are treated as a global overhead and thus removed from the available emission budgets prior to developing the pathways. if anything. given most Annex 1 countries have already deforested (emitting CO2 ) it could twentieth century emissions from Annex 1 nations into calculations of the ‘fair’ emission space available for Annex 1 in the twenty-first century would leave Annex 1 nations already in ‘emission debt’. it evidently would not provide for a politically consensual framing of emission apportionment. As it stands. However. a case could be made for considering the responsibility for twentieth century emissions in apportioning future twenty-first century emission-space between Annex 1 and non-Annex 1 regions. While the following analysis focuses specifically on the period 2000–2100. the implications of including twentieth century emissions and the concept of emission debt may guide the scope and scale of climate-related financial transfers (arguably as reparation) between Annex 1 and non-Annex 1 nations.Downloaded from rsta. Phil. Building on this cumulative emissions per capita approach.org on December 27. errs in favour of the Annex 1 nations.

All scenario pathways ((a) C+1. 2010 30 (a) 50 40 GtCO2 yr–1 30 20 10 0 2000 2020 2040 2060 2080 2100 year K. 98 per cent by 2050. (b) C+2. CO2 emissions associated with international bunkers and deforestation are included. the updated estimate used for this paper (266 GtCO2 over the twenty-first century) continues in this optimistic vein. non-Annex 1. but updated to include the most recent emission estimates provided by the Global Carbon Project [41]. The global overhead approach applied here does not absolve non-Annex 1 nations of responsibility for deforestation emissions. CO2 scenarios for approximately 37% chance of not exceeding 2◦ C. This scenario pathway results in a 56 per cent reduction from 1990 levels in emissions for Annex 1 nations by 2020.Downloaded from rsta. dotted line. For global emissions to remain within the budget. also be considered unreasonable to ascribe all of the non-Annex 1 deforestation emissions solely to non-Annex 1 nations. as their available budget for energy-related emissions. global including deforestation). While non-CO2 greenhouse gases are not included in the C+ scenario pathway. Annex 1. non-Annex 1 nations’ emissions still need to decline at 6 per cent per year following their peak in 2020 if global emissions are to remain within the cumulative budget. A (2011) (c) CO2 plus (C +) . will be reduced as a consequence of the emissions from deforestation. 11% per year). Soc. red line. Bows (b) (c) 2000 2020 2040 2060 2080 2100 year 2000 2020 2040 2060 2080 2100 year Figure 1. (c) C+3) are for the same cumulative twenty-first century CO2 budget of 1321 GtCO2 (blue line.royalsocietypublishing. Non-Annex 1 nations increase their emissions to 71 per cent higher than Phil. The original Anderson and Bows scenarios were optimistic compared with scenarios within the literature. Annex 1 nations are assumed to reduce their emissions from 2011 onwards towards virtually complete decarbonization by 2050. The first three scenario pathways (C+ pathways 1–3 shown in figure 1) use the lowest CO2 budget from Macintosh [3]. Anderson and A. R. along with the budget for Annex 1 nations’ energy emissions. The deforestation scenario used throughout the paper is taken as an average of the two scenarios used within Anderson & Bows [2].org on December 27. Trans. C+1 assumes non-Annex 1 emission growth continues at lower than economic downturn rates from 2010 to 2015 (3% per year) and that emissions peak in 2020. The second three (C+ pathways 4–6 in figure 2) use the mid-level CO2 budget from the same paper. Despite such significant reductions in Annex 1 nations (approx. All C+ scenario pathways take the development of emissions within the nonAnnex 1 nations as the starting point and then build a related Annex 1 emission pathway that holds CO2 emissions within the chosen budget.

Kyoto gas scenarios for approximately 39–48% chance of not exceeding 2◦ C ((a) B6 1 not viable). R. dotted line.org on December 27.28] this scenario pathway is estimated to have a 36 per cent20 probability of exceeding 2◦ C. and peak in 2025. (c) C+6) are for the same cumulative twenty-first century CO2 budget of 1578 GtCO2 (blue line. 21 Given it is not possible to have an immediate cessation of emissions from all Annex 1 nations. non-Annex 1. Using the PRIMAP tool developed by Meinshausen et al. this scenario pathway is not compatible with the lower of the cumulative carbon budgets. probabilities may vary slightly for the same twenty-first century budget. the cumulative twenty-first century CO2 e budget is 2202 GtCO2 e (blue line. ‘best estimates’ are presented. For (b) B6 2.21 20 PRIMAP provides a range of probabilities and a ‘best estimate’ using cumulative emissions between 2000 and 2049. All scenario pathways ((a) C+4. Annex 1. Soc. A (2011) . red line. owing to differences in the 2000–2049 emissions. Thus. 2010 Beyond dangerous climate change (a) 50 40 GtCO2 yr–1 30 20 10 0 2000 2020 2040 2060 2080 2100 year 31 (b) (c) 2000 2020 2040 2060 2080 2100 year 2000 2020 2040 2060 2080 2100 year Figure 2. dotted line. However. non-Annex 1. Following the same approach. Trans. [7. C+2 has non-Annex 1 emissions continuing to grow at a lower than pre-economic downturn rate until 2020 (3% per year). CO2 scenarios for approximately 50% chance of not exceeding 2◦ C. Phil. (b) C+5. non-Annex 1 nations use the entire carbon budget and leave no emission budget for Annex 1 nations. Here.royalsocietypublishing. if this is the case. Annex 1.Downloaded from rsta. global including deforestation). (a) 50 40 GtCO2e yr–1 30 20 10 0 2000 (b) 2020 2040 2060 year 2080 2100 2000 2020 2040 2060 year 2080 2100 Figure 3. red line. total including deforestation). 1990 levels by 2020 and then reduce them to 76 per cent below 1990 levels by 2050.

in this case. Global emissions thus peak in 2019 with Annex 1 emissions 6 per cent below 1990 by 2020 and 84 per cent by 2050. Within this scenario pathway. A (2011) . In addition to considering the effect of non-CO2 greenhouse gases contributing to the overall budget. Following the dip in emissions owing to the economic downturn. global emissions are broadly flat between 2014 and 2022. Bows To explore the potential of providing for more acceptable reduction rates while still offering a ‘reasonable’ chance of not exceeding 2◦ C. all B6 pathways (figures 3 and 4) take the development of emissions within the non-Annex 1 nations as the starting point and then build a related Annex 1 emission scenario pathway that must.royalsocietypublishing. This scenario pathway has an estimated 50 per cent chance of exceeding 2◦ C according to PRIMAP [28]. To remain within budget. Given this. although emissions are highest in 2020. Global emissions are 67 per cent below 1990 by 2050. This plausible but highly unlikely scenario has a 37 per cent chance of exceeding 2◦ C according to PRIMAP [28]. Both Annex 1 and non-Annex 1 emissions are assumed to decline post-peak at 5–6% per year. Non-Annex 1 emissions are 186 per cent above 1990 levels in 2020 and 45 per cent below them by 2050. no emission space is available for Annex 1 nations. C+6 uses the same higher budget but illustrates that if reductions are lower.2 billion global population (based on UN Phil. and if Annex 1 emissions begin to reduce immediately (as in C+1). R. 2010 32 K.Downloaded from rsta. non-Annex 1 nations’ emissions must still reduce at 7–8% per year after the peak date in order for global emissions to remain within the cumulative budget. The significant difference between the B6 and the C+ pathways is that the given emission budget is assumed to apply to the full basket of 6 greenhouse gases mirroring the approach taken in Anderson & Bows [2]. and peak in 2025 with a rapid decline to a maximum of 7–8% per year. Anderson and A. Soc. Trans. Annex 1’s emissions peak by 2010 and decline at 7–8% per year. C+5 again uses the higher budget within Macintosh [3] but assumes nonAnnex 1 emissions to continue to grow at 4 per cent per year rates until 2020. C+4 assumes non-Annex 1 nation emissions grow at 4 per cent per year until 2015 peaking in 2020. C+5 has a 52 per cent chance of exceeding 2◦ C. and as a result of a step-change in emission growth from non-Annex 1 nations. an essential difference is the requirement for significant emissions space post-2050 to allow for greenhouse gas emissions (specifically N2 O and CH4 ) associated with food production for an approximate 9. The Annex 1 nations have more room to grow in early years than in C+1. C+3 assumes nonAnnex 1 nations’ emissions grow at a much reduced rate (1% per year) until 2025.org on December 27. keep total greenhouse gas emissions within the chosen budget. global emissions peak in 2011 and Annex 1 nations’ future emissions do not grow any higher than current levels. Thus the penalty for a five year delay in the non-Annex 1 peak date is an additional 2 per cent per year on top of the emission reduction rate for both Annex 1 and non-Annex nations. (d) Basket of six scenario pathways (B6) In a similar approach to the C+ pathways. The next three scenario pathways (figure 2) use the higher budget of 1578 GtCO2 within Macintosh [3]. at 4–5% per year for non-Annex 1 nations following the peak date. but are assumed to reach a peak by 2015. in addition to an immediate Annex 1 reduction.

1 GtCO2 e. emissions from 2017 onwards for non-Annex 1 nations must tend immediately towards the emissions floor of 5. The cumulative twenty-first century CO2 e budget is 2202 GtCO2 e.1 GtCO2 e as a minimum annual greenhouse gas emission for non-Annex 1 nations and 0. red line.67 tCO2 e per person from 2050 onwards for food-related nonCO2 greenhouse gases compared with an approximate figure of 0. the assumed minimum level of greenhouse gas production related to food is more optimistic still at 6 GtCO2 e per year as opposed to 7. The PRIMAP tool to estimate the probability of exceeding the 2◦ C threshold assumes the vast majority of emissions are released pre-2050 (fig.org on December 27. dotted line. Soc. This is in line with the value chosen by the UK [8] and results in an estimated 0. 2 in [7]). B6 2 makes identical assumptions to B6 1 but for the ‘high’ IPCC emission budget (figure 3). (b) B6 4).3 billion in Annex 1 nations [46]. A (2011) . total including deforestation. B6 1 uses the IPCC ‘low’ emission budget and assumes that between 2010 and 2015 non-Annex 1 emissions grow at slightly lower (3% per year) than preeconomic downturn rates and peak by 2020 (figure 3). Trans. Assuming by 2050 there are 7.Downloaded from rsta.46]. Given the food-related nonCO2 greenhouse gases post-2050.5 GtCO2 e per year. Emission reductions for non-Annex 1 nations in this case are 6 per cent per year. and 1. 2010 Beyond dangerous climate change (a) 50 40 GtCO2e yr–1 33 (b) 30 20 10 0 2000 2020 2040 2060 year 2080 2100 2000 2020 2040 2060 year 2080 2100 Figure 4. median estimate for 2050 [46]). where non-Annex 1 emissions peak in 2020.royalsocietypublishing. Annex 1. non-Annex 1. The additional space allowed leads to a viable scenario pathway. this scenario pathway is not viable.9 billion people in nonAnnex 1 nations. In an update to the previous Anderson & Bows [2] study. Blue line. and assuming food consumption is more evenly balanced between Annex 1 and non-Annex 1 nations than currently. Given that within the B6 scenario pathways there is a substantial cumulative emission total for the post2050 emissions (with at least 300 GtCO2 e from greenhouse gases associated with Phil.95 GtCO2 e per person for 2010 [44. In other words. while for Annex 1 they gradually build from around 3 per cent per year for 2015 to 2020 to 6 per cent later in the century. Kyoto gas scenarios for approximately 38–48% chance of not exceeding 2◦ C ((a) B6 3. R. while Annex 1 nation emissions decline from 2010 onwards.86 GtCO2 e per year for Annex 1 nations. this would allow approximately 5.

pathways are constructed that assume non-Annex 1 nations’ emissions continue to develop along their current trajectory until 2025. For example. 2010 34 K. Phil. More gradual reductions in emissions from non-Annex 1 nations would render this scenario pathway impossible. — The amount of non-CO2 greenhouse gas emissions released per year possible post-2050 is 6 GtCO2 e (in line with assumptions made by the UK CCC [8]) of which 3 GtCO2 e per year is from N2 O. — Thus 150 GtCO2 e of cumulative emissions are added to the pre-2050 emissions to estimate an alternative probability. following a levelling off of emissions until 2014. This scenario pathway has at least a 38 per cent probability of exceeding 2◦ C. If 150 GtCO2 e is added to the cumulative emission total for each scenario. Trans. A (2011) 22 This . B6 3 assumes non-Annex 1 nation emissions peak in 2025 following a growth of 3 per cent per year between 2010 and 2020 (figure 4). inputting the 2000–2049 cumulative total for each B6 scenario into PRIMAP will result in an underestimate of the probability of exceeding 2◦ C. and potentially as high as 47 per cent once post-2050 emissions are factored in. then reducing at is an explicitly conservative assumption and results in slightly higher probabilities of not exceeding 2◦ C than would be the case if some allowance were to be made for post-2050 emissions of methane. To account for this underestimate. With steep emission reductions for non-Annex 1 nations post-peak of 6 per cent per year. PRIMAP estimates an approximate ten percentage point increase in probability of exceeding 2◦ C (see table 1. Bows food production).22 — N2 O and methane each account for approximately 50 per cent of the nonCO2 greenhouse gases post-2050 (Smith. For both the C+ and B6 regimes. Both B6 3 and B6 4 take the IPCC’s ‘high’ cumulative budget as a constraint.Downloaded from rsta. — The shorter-lived nature of methane compared with N2 O results in a negligible impact on post-2050 warming from methane. (e) Orthodox scenario pathways The final scenario pathways developed are unconstrained by a particular emission budget (figure 5). B6 3 has the same probability of exceeding 2◦ C as B6 2. The emission reductions post-peak for non-Annex 1 nations are 4–5% per year. B6 2 has at least a 39 per cent chance of exceeding 2◦ C and is potentially as high as 48 per cent. an alternative probability is calculated assuming the following. with considerably slower growth of 1 per cent per year until a peak date in 2025 (figure 4). Anderson and A. Annex 1 nations would need to reduce emissions from 2010 onwards at more than 10 per cent per year to remain within the high IPCC cumulative budget. R. emissions decrease at 6 per cent per year. peaking in 2030.royalsocietypublishing. figure is in brackets). Soc. whereas for Annex 1 nations.org on December 27. personal communication). B6 4 mirrors the assumptions within C+3.

2010 orthodox B6 [3662] a These b This 35 scenario pathways are not viable as they could not remain within the carbon budget prescribed. A (2011) 37% 50% 52% — — 39% (48%)d 39% (48%)d 38% (47%)d 88% 88% (92%)d +223% (+163%) 3% 2007 313 2007 139 2007 313 2007 532 2007 363 2007 153 2007 [265] 2010 [639] 2007 [429] 2007 [552] 2015 [729] 2015 [891] 2020 742 2025 916 2025 742 2020 780 2025 949 2025 1159 2017 [841] 2020 [1293] 2025 [1503] 2025 [1380] 2030 1747 2030 [2501] C+1 1321 C+2a 1321 C+3 1321 C+4 1578 C+5 1578 C+6a 1578 B6 1a. scenario pathway 2012 2007 2007 2019 2020 2024 2017 2017 2013–2018 57% (95%) 2013 2027 2028 5% (62%) 2% (60%) 34% (90%) +154% (24%) +111% (17%) 25% (82%) +135% (46%) 95% (95%) 61% (61%) — 4–6% 8–10% 6% 100% (100%) +220% (+38%) — 44% (95%) +220% (32%) 8% 7–8% 4–5% — 5–6% 6–7% 4–5% 3% +180% (128%) 3% 3% 6% (84%) +186% (45%) 5–6%b 5–6% 56% (98%) +143% (54%) 10–11% 7–8% 7–8% 5–6% 7–8% 4–5% — 3% 4–5% 4–5% 3% 3% 100% (100%) +193% (27%) — 6–7% 6–7% 56% (98%) +1714% (54%) 10–11% 6–7% 6–7% global 21st century CO2 or greenhouse gas budget in GtCO2 or [GtCO2 e] Annex 1 % reduction on 1990 levels by 2020 (2050) 36% non-Annex 1 % reduction on 1990 levels by 2020 (2050) Annex 1 peak date/21st century cumulative emissions in GtCO2 or [GtCO2 e] non-Annex 1 peak date/21st century cumulative emissions global peak in GtCO2 or [GtCO2 e] date approximate % of exceeding post-peak 2◦ C (based on post-peak post-peak global rate of 2000–2049 Annex 1 non-Annex 1 reduction emissions rate of rate of (includes using reduction reduction deforestation) PRIMAP) Phil. . R. Summary of scenario pathway characteristics. Trans. c All B6 scenario pathways assume an ‘emission floor’ of 6GtCO e for food-related emissions for an approximate 9 billion population post-2050 until 2 2100. Soc.Table 1. is the reduction rate following the period of relatively stable emissions until 2016.org on December 27. emission reduction rates would be altered for the same cumulative values.royalsocietypublishing. d The figure in brackets illustrates a higher probability to take into account the ongoing emissions associated with food production as opposed to greenhouse gas emissions tending to zero.c [1376] B6c 2 [2202] Beyond dangerous climate change B6c 3 [2202] B6c 4 [2202] orthodox C+ 2741 Downloaded from rsta. If a different ‘emission floor’ were to be used.

2. p. has post-peak emissions reducing at 3. R. 32].org on December 27. 2010 36 (a) 60 K.Downloaded from rsta. thus a reasonable probability of exceeding 4◦ C. Cumulative emissions of approximately 2700 GtCO2 are associated with stabilization of 550 ppmv CO2 . emissions are assumed to be relatively stable with a peak in 2016 and subsequent emission reductions of 3 per cent per year. cumulative emissions of CO2 alone are 2. Anderson and A. Stern concludes ‘it is likely to be difficult to reduce emissions faster than around 3 per cent per year’ [6. For the Annex 1 nations. The most stringent of the ADAM scenarios assumed emission reduction rates of approximately 3 per cent per year between a 2015 peak and 2050 [47 fig. Discussion (a) CO2 plus (C+) Although six C+ pathways were developed in the previous section. Orthodox B6 has cumulative emissions of greenhouse gases of 3662 GtCO2 e. total including deforestation. 5. their twenty-first century cumulative budgets suggest the future temperature increase compared with pre-industrial times is more likely to be of the order of 4◦ C rather than 2◦ C. red line. One exceeded the lower of the two chosen 23 The pathway of the CCC’s [8] most challenging scenario. ‘2016:4% low’. Figures in excess of 3500 GtCO2 e can be assumed to be closer to the 750 ppmv range.741 GtCO2 . Blue line. Emission scenarios for approximately 88–92% chance of not exceeding 2◦ C. Soc. a rate considered politically and economically acceptable23 (3% reduction per year). Furthermore. For orthodox C+. Both plots illustrate ‘orthodox’ mitigation pathways with (a) C+ for CO2 only (twenty-first century cumulative emissions: 2741 GtCO2 ) and (b) B6 for Kyoto gases (twenty-first century cumulative emissions: 3662 GtCO2 e). Trans. Stern [6] states ‘there is likely to be a maximum practical rate at which global emissions can be reduced’ pointing to ‘examples of sustained emissions cuts of up to 1 per cent per year associated with structural change in energy systems’ and that ‘cuts in emissions greater than this (1%) have historically been associated only with economic recession or upheaval’. two were rejected for exceeding the constraints on cumulative CO2 budgets related to the 2◦ C temperature threshold. 201–204]. pp. Phil. non-Annex 1. Bows (b) GtCO2e yr–1 40 20 0 2000 2020 2040 2060 year 2080 2100 2000 2020 2040 2060 year 2080 2100 Figure 5.royalsocietypublishing. dotted line.5 per cent per year from all sources. Annex 1. A (2011) . These scenario pathways both result in an 88 per cent chance of exceeding the 2◦ C threshold (potentially 92% for orthodox B6).

Annex 1 emissions continue to decline following the current economic downturn at rates in excess of 5 per cent per year. given a significant portion of emissions are attributable to food production post-2050. it is more Phil. emission reductions of 6 per cent per year for both Annex 1 and non-Annex 1 nations are necessary if nonAnnex 1 emissions continue at recent growth rates and peak in 2020. A (2011) . (b) Basket of six (B6) When developing the B6 pathways (figures 3 and 4). with a more probable figure closer to 48 per cent. post-peak emission reductions of 4–5 per cent per year are still needed from the aggregate of all nations. 50% of not exceeding 2◦ C) because. under the IPCC’s higher budget. if these rates are sustained for a further five years (i. For the IPCC’s ‘high’ end of the range. Consequently. However. it became apparent immediately that the ‘low’ IPCC cumulative emission value was not viable if non-Annex 1 emissions peak as late as 2020. to 1%.org on December 27. Therefore. This result is in line with the scenario pathway analysis within Anderson & Bows [2]. Those pathways remaining within the lower budget required an immediate and rapid decline in Annex 1 emissions and an early peak in non-Annex 1 emissions. Even if non-Annex 1 emissions grow at much slower rates to a 2025 peak. post-peak emission reductions of 4–5% per year were insufficient to stay within the cumulative budget. 37% of not exceeding 2◦ C) owing to non-Annex 1 emissions both continuing with recent growth rates out to 2020 and peaking in 2025. Furthermore. 2010 Beyond dangerous climate change 37 budgets (approx. to 2025). Even if Annex 1 nations agree on the scale of necessary emission reductions. Given these pathways explicitly exclude non-CO2 greenhouse gas emissions. In all cases. Trans. the minimum probability of not exceeding the 2◦ C threshold achievable in this scenario pathway set is 38 per cent. compared with current growth of 3–4% per year [48]). and nonAnnex 1 post-peak reductions are 6 per cent per year or less. the rates of reduction for CO2 presented in table 1 illustrate the change necessary within the energy system primarily.e. figure 2 and table 1 illustrate that a 5 year delay in the peak year for non-Annex 1 nations (from 2020 to 2025) forces a 2 per cent increase in reduction rates globally in addition to an immediate emission reduction for Annex 1 nations. all viable scenario pathways exhibit emission reduction rates well in excess of those typically considered to be politically and economically feasible.royalsocietypublishing. there continues to be an absence of any meaningful global action to mitigate emissions or set binding targets. R. in addition to the emissions growth and peak years. unless the latter’s emission growth was constrained to rates much lower than historical trends (i.Downloaded from rsta. 50%) chance of not exceeding 2◦ C. Moreover.e. The other surpassed the higher of the two cumulative budgets (approx. For the higher (approx. Soc. no emissions space remains for Annex 1 nations. this probability is likely to be a significant underestimate. figures 1 and 2 illustrate the need for complete decarbonization of the Annex 1 energy system by around 2050. (c) Orthodox In light of the recent Copenhagen negotiations.

A (2011) . the overarching data and trend lines underpinning Köne and Büke’s analysis were available at the time many of the scenarios were developed. it is unlikely that emission growth rates will be significantly moderated during the coming decade. this despite irrefutable evidence to the contrary [48]. To explore the implications of this. are more closely aligned with much higher climate change futures associated with at least 3–4◦ C of warming. R. For example. it is perhaps surprising they are central to so many scenarios. slow action to mitigate emissions on the part of Annex 1 nations. 27 The inclusion of bio-CCS also demonstrates a degree of non-contextual engagement with technology. while it may be argued that the latter approach benefits from greater internal consistency and more theoretically coherent parameters. Although these will go some way towards addressing future high-carbon lock-in. These bio-CCS scenarios all included wider CCS facilities. Phil.14] illustrate the non-contextual framing that typifies much of this form of analysis. Of the principal 450 ppmv scenarios reviewed. no CCS power plants have yet being built and consequently large-scale CCS remains a theoretical possibility with no operating experience of capture rates (though many of the component processes have undergone testing).27 At least half of the scenarios relied on significant levels of ‘overshoot’ (between 500 and 590 ppmv CO2 e)28 and 24 Though constrained explicitly to consider top-down emissions only with coarse high-level divisions between food.org on December 27. recent overviews of scenarios generated by a range of different international integrated assessment modelling communities [10. (d) Simple and complex scenarios The scenarios developed in this paper are relatively contextual24 and as such complement the wealth of scenarios from more non-contextual integrated assessment models. deforestation.Downloaded from rsta. This non-contextual approach to technology extends to nuclear power. 2010 38 K. the two orthodox scenario pathways paint a picture of ongoing nonAnnex 1 emission growth. yet were without detailed analysis of potentially significant constraints on storage capacity. included as a ‘key energy supply technology’ in all but one of the 450ppmv scenarios reviewed. Given the many unknowns around bio-CCS. Resulting cumulative emissions. Trans. Aside from the considerable bio-energy debate surrounding the sustainability of biofuels. Soc. energy and industrial processes.26 Over a third factored in negative emissions through the inclusion of geo-engineering in the form of ‘biomass with carbon capture and storage’ (CCS) technologies. 25 Bottom-up and built on typically idealized inputs with only limited regard for ‘real-world’ constraints. the majority had a global emissions peak in 2010. Bows probable that non-Annex 1 nations will set targets based on levels of carbon or energy intensity improvements.25 However. the outputs are typically removed from the political and empirical reality within which responses to climate change are developed. 26 While Köne & Büke’s [48] paper was published after many of the scenarios referred to. here too the integrated assessment modelling approach typically treats these wider concerns as exogenous and resolvable. and then sustained emission reductions at rates considered politically and economically feasible. Whilst sufficient uranium exists for moderate increases in conventionally fuelled reactors. Anderson and A.royalsocietypublishing. while still within the bounds of possibility of not exceeding the 2◦ C threshold (8–12% chance). significant ramping up of nuclear capacity is likely to require fast breeder reactors with major challenges associated with their widespread introduction.

Soc. at first sight.29 The non-contextual framing of many complex modelling approaches (including integrated assessment modelling). 6. allied with their inevitable opaqueness and often abstract and implicit assumptions. only the global economic slump has had any significant impact in reversing the trend of rising emissions. the division related to Annex B regions.org on December 27. the difference in responses is related less to different interpretations of the science underpinning climate change and much more to differing assumptions related to five fundamental and contextual issues. Phil. appears to be the same question: what emissionreduction profiles are compatible with avoiding ‘dangerous’ climate change? However. However. if they exist at all.g. with Annex 1 and non-Annex 1 nations returning rapidly to their earlier economic and emissions trajectories and with the failure of Copenhagen to achieve a binding agreement to reduce emissions in line with 2◦ C. Trans. Conclusions Over the past five years a wealth of analyses have described very different responses to what. (1) (2) (3) (4) (5) What delineates dangerous from acceptable climate change? What risk of entering dangerous climate change is acceptable? When is it reasonable to assume global emissions will peak? What reduction rates in post-peak emissions is it reasonable to consider? Can the primacy of economic growth be questioned in attempts to avoid dangerous climate change? 28 Overshoot scenarios remain characterized by considerable uncertainty and are the subject of substantive ongoing research (e. on closer investigation.50]). R. Making explicit the implications of particular assumptions (such as peak emission dates or very low probabilities of exceeding 2◦ C) provides insights that not only are intelligible to wider stakeholders and decision-makers. For all practical purposes aggregated emissions related to Annex 1 are the same as those for Annex B. leaves space for the simpler. the conclusions arising from this paper are significantly bleaker than those of the authors’ 2008 paper. the prospects for avoiding dangerous climate change. A (2011) . more transparent and contextual approach to scenarios presented in this paper. are increasingly slim.Downloaded from rsta. [49. Furthermore. In both these regards and with the continued high-level reluctance to face the real scale and urgency of the mitigation challenge. despite the actual date being around 2006. disaggregating global into Annex 1 and nonAnnex 1 emission pathways only serves to exacerbate the scale of this disjuncture between the rhetoric and reality of mitigation. 29 Within the integrated assessment modelling scenarios referred to. but can also provide ‘contextual’ parameters and constraints to more complex modelling approaches. 2010 Beyond dangerous climate change 39 several assumed fossil fuel CO2 emissions from non-Annex 1 nations would exceed those from Annex 1 as late as 2013–2025 [14]. (e) Development on the authors’ 2008 paper Two years on from earlier analysis by Anderson & Bows [2].royalsocietypublishing.

Downloaded from rsta. while the rhetoric of policy is to reduce emissions in line with avoiding dangerous climate change. For example.royalsocietypublishing. on closer examination these analyses suggest such reduction rates are no longer sufficient to avoid dangerous climate change. the CCC [8] and ADAM [47]. Soc. R. in discussing arguments for and against carbon markets the CCC state ‘rich developed economies need to start demonstrating that a low-carbon economy is possible and compatible with economic prosperity’ [8. Bows While (1) and. 30 Regions can evidently identify what may constitute dangerous within their geographical boundaries. p. 33 With policies themselves lagging even further behind in terms of both actual reductions achieved or planned for.org on December 27. Trans. then would it be more reasonable to characterize ‘1◦ C as the new 2◦ C’ ? 32 Assuming the logic for the 2◦ C characterization of what constitutes dangerous still holds. and despite the evident logic for revising the 2◦ C threshold. Phil. conceding that avoiding dangerous (and even extremely dangerous) climate change is no longer compatible with economic prosperity. at their most crude level. However. Despite such clarity. the CCC are. Nevertheless. those providing policy advice frequently take a much less categorical position. However. but given many impacts (and the responsibility for them) extend well beyond such boundaries any regional assessment needs to be within the context of a more global perspective.33 This already demanding conclusion becomes even more challenging when assumptions about the rates of viable emission reductions are considered alongside an upgrading of the severity of impacts for 2◦ C.21]. In stark contrast.31 there is little political appetite and limited academic support for such a revision. the recent reassessment of these impacts upwards suggests current analyses of mitigation significantly underestimate what is necessary to avoid dangerous climate change [20. many academics and wider policy advisers undertake their analyses of mitigation with relatively high probabilities of exceeding 2◦ C and consequently risk entering a prolonged period of what can now reasonably be described as extremely dangerous climate change. given that it is a ‘political’ interpretation of the severity of impacts that informs where the threshold between acceptable and dangerous climate change resides. 160].32 Put bluntly.30 the latter three have pivotal regional dimensions that. such as those developed by Stern [6]. Anderson and A. In relation to the first two issues. the Copenhagen Accord and many other highlevel policy statements are unequivocal in both their recognition of 2◦ C as the appropriate delineator between acceptable and dangerous climate change and the need to remain at or below 2◦ C. although the implications of their more nuanced analyses are rarely communicated adequately to policy makers. annual rates of emission reduction beyond the peak years are constrained to levels thought to be compatible with economic growth—normally 3 per cent to 4 per cent per year. can be understood in relation to Annex 1 and non-Annex 1 emission profiles. given the CCC acknowledge ‘it is not now possible to ensure with high likelihood that a temperature rise of more than 2◦ C is avoided’ and given the view that reductions in emissions in excess of 3–4% per year are not compatible with economic growth. Moreover. Within global emission scenarios. most policy advice is to accept a high probability of extremely dangerous climate change rather than propose radical and immediate emission reductions. A (2011) . 2010 40 K. to a lesser extent. 31 If the impacts are to remain the principal determinant of what constitutes dangerous. (2) are issues for international consideration. in effect.

Stern and ADAM analyses. particularly those directly informing policy. R. it is often allied with biomass combustion to provide ‘negative’ emissions (§5d). 2010 Beyond dangerous climate change 41 In prioritizing such economic prosperity over avoiding extremely dangerous climate change. Real hope and opportunity. a profound departure from the more ‘feasible’ assumptions framing the majority of such reports. There is now little to no chance of maintaining the rise in global mean surface temperature at below 2◦ C. 35 With the only exception being C+4 where Annex 1 emissions are stable until 2016. [20. sufficiently so that 2◦ C now more appropriately represents the threshold between dangerous and extremely dangerous climate change.org on December 27. do global emissions peak by 2020. in 2010. the CCC. Phil. remains untried for a large scale power station. The analysis within this paper offers a stark and unremitting assessment of the climate change challenge facing the global community. at least temporarily. which. All premise their principal analyses and economic assessments on the ‘infeasible’ assumption of global emissions peaking between 2010 and 2016.g. Without such negative emissions. Consequently. reducing thereafter. Moreover. despite repeated high-level statements to the contrary. A (2011) 34 The . Soc. this paper is not intended as a message of futility. if it is to arise at all.royalsocietypublishing. will do so from a raw reference to ‘feasible’ technologies typically extends to carbon capture and storage. 2010 represents a political tipping point. However. 36 In essence. The science of climate change allied with emission pathways for Annex 1 and non-Annex 1 nations suggests a profound departure in the scale and scope of the mitigation and adaption challenge from that detailed in many other analyses. as the scenario pathways developed within this paper demonstrate. Stern. Consequently. the 2010 global peak central to many integrated assessment model scenarios as well as the 2015–2016 date enshrined in the CCC. Trans. The scale of this departure is further emphasized when disaggregating global emissions into Annex 1 and non-Annex 1 nations. do not reflect any orthodox ‘feasibility’. By contrast. while in terms of emission reduction rates their analyses favour the ‘challenging though still feasible’ end of orthodox assessments. the approach they adopt in relation to peaking dates is very different. the logic of such studies suggests (extremely) dangerous climate change can only be avoided if economic growth is exchanged. but rather a bare and perhaps brutal assessment of where our ‘rose-tinted’ and well intentioned (though ultimately ineffective) approach to climate change has brought us.g. for a period of planned austerity within Annex 1 nations36 and a rapid transition away from fossil-fuelled development within non-Annex 1 nations. and with tentative signs of global emissions returning to their earlier levels of growth. ADAM and similar analyses suggest they are guided by what is feasible. several of the major analyses (e.34 However. Only if Annex 1 nations reduce emissions immediately35 at rates far beyond those typically countenanced and only then if non-Annex 1 emissions peak between 2020 and 2025 before reducing at unprecedented rates. [9.Downloaded from rsta.10]) will have increased cumulative emissions and hence further increased probabilities of exceeding 2◦ C (see also footnote 27). a planned economic contraction to bring about the almost immediate and radical reductions necessary to avoid the 2◦ C characterization of dangerous climate change whilst allowing time for the almost complete penetration of all economic sectors with zero or very low carbon technologies. the impacts associated with 2◦ C have been revised upwards (e. Moreover.21]).

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