You are on page 1of 26

Downloaded from rsta.royalsocietypublishing.

org on December 27, 2010

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

References This article cites 22 articles, 4 of which can be accessed free
http://rsta.royalsocietypublishing.org/content/369/1934/20.full.h
tml#ref-list-1

Article cited in:
http://rsta.royalsocietypublishing.org/content/369/1934/20.full.html#rel
ated-urls

This article is free to access

Rapid response Respond to this article
http://rsta.royalsocietypublishing.org/letters/submit/roypta;369/
1934/20

Subject collections Articles on similar topics can be found in the following
collections

atmospheric chemistry (9 articles)
environmental engineering (22 articles)

Email alerting service Receive free email alerts when new articles cite this article - sign up
in the box at the top right-hand corner of the article or click here

To subscribe to Phil. Trans. R. Soc. A go to:
http://rsta.royalsocietypublishing.org/subscriptions

This journal is © 2011 The Royal Society

Downloaded from rsta.royalsocietypublishing.org on December 27, 2010

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 AND ALICE BOWS2, *
1 TyndallCentre 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 non-
Annex 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’.

20 This journal is © 2011 The Royal Society

[11–13]). quantified economy-wide emissions targets for 2020’. R. Moreover. the Accord recognizes ‘that the time frame for peaking will be longer in developing countries’ and also. Building particularly on previous analyses by Anderson & Bows [2] and more recently by Macintosh [3]. it is assumed that the ‘2 degrees Celsius’ relates to the temperature rise above pre-industrial levels. that ‘social and economic development and poverty eradication are the first and overriding priorities of developing countries’. electricity and transport within Annex 1 nations coupled with the very rapid industrialization of many non-Annex 1 nations. By considering global emission budgets alongside emission pathways for non-Annex 1 nations. and considers these in light of post-2000 and recession-adjusted emission trends. 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 . While the inclusion of nearer-term targets is certainly a welcome complement to targets for 2050. very significantly.g. integrating national and global analyses is a prerequisite of understanding the scale and rate of mitigation. however. Trans.g. Phil. 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.g. . Analysis framing The first decade of the new millennium has witnessed unprecedented increases in emissions reflecting ongoing high levels of energy usage for heat. this paper illustrates the increasing relevance of the latter for the mitigation policies of Annex 1 nations. 2010 Beyond dangerous climate change 21 consistent with science and on the basis of equity’ [1]. as it stands.royalsocietypublishing. the Accord makes no mention of cumulative emissions as providing the scientifically credible framing of mitigation.5]). Clearly.3.org on December 27. Soc. such integration is rare with 1 For the purpose of this paper. 2. [2. Alongside these global analyses a growing range of ever more detailed national-level energy and emission scenarios are being developed (e. 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.1 The Accord does not. in particular China and India. this dramatic potential for emissions growth within non-Annex 1 nations is typically neglected in global and national mitigation scenarios. Downloaded from rsta. the Accord still falls short of acknowledging what the science makes absolutely clear—it is cumulative emissions that matter. and despite making reference to being guided by the ‘science’. 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. each with a differing quantity of cumulative emission over the twenty-first century and hence with different temperature implications (e. A (2011) . Although included in non-mitigation energy scenarios (e. Recent years have seen the development of an increasing number of global emissions scenarios. though this is not made clear in the Accord. the paper translates earlier global assessments of cumulative emissions into emission pathways for Annex 1 and non-Annex 1 nations. However.6–10]). [4. Specifically. . The importance of the distinction between Annex 1 and non-Annex 1 is also noted in the Accord. impacts and adaptation associated with differing levels of climate change.

2010 22 K. Trans. For example. but does offer clear guidance as to the scale and rate of mitigation necessary to avoid particular rises in temperature above pre-industrial levels. p. EU and the UK do not make explicit what quantitative ‘risk’ of exceeding 2◦ C is considered ‘acceptable’. to ensure that global average temperature increases do not exceed preindustrial levels by more than 2◦ C’ [15] (emphasis added). and given current trends and agreements. probabilities may be inferred based on the approach developed for the Intergovernmental Panel on Climate Change’s (IPCC’s) reports.g. at least a very low one [16]. The EU maintains it ‘must adopt the necessary domestic measures . the language of many Government statements suggests. The previous Secretary of State for Energy and Climate Change. . 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). hence. subsequently reiterated this commitment. 5] (emphasis added). in which it stated explicitly that ‘to avoid the most dangerous impacts of climate change. 23]. The third considers how a slower uptake of mitigation measures combined with later emissions peaking impact on cumulative emissions and. Downloaded from rsta. Soc.2 Such analysis cannot substitute for detailed national-level assessments. By disaggregating selected global emission pathways into Annex 1 and non-Annex 1 nations. EU’s and UK Government’s 2 Similar but less-contextual analyses also illustrate the division of global emissions between Annex 1 and non-Annex 1 nations (e. whereby a correlation is made between the language of likelihood and quantified probabilities [19. . Bows little more than perfunctory correlation between national and global emission pathways. Although this language is qualitatively clear. average global temperatures must rise no more than 2◦ C’ [17. the Accord.3 The paper comprises three principal analyses. . . in July 2009. R. 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.royalsocietypublishing.g. Anderson and A. However. their per capita emissions are around one fifth of those for the USA. A (2011) . 3 It 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. (a) Determining the ‘appropriate’ probability for 2◦ C The framing of the Copenhagen Accord around the importance of ‘hold[ing] to . Ed Miliband. the Accord’s. below 2 degrees Celsius’ reflects the clear and long-established stances of both the European Union (EU) Commission and the UK Government. whilst China’s total emissions are now higher than those from any other nation. Within the UK.org on December 27. the UK Government published its UK Low Carbon Transition Plan. The first derives pathways for CO2 emissions consistent with reasonable-to-low probabilities of exceeding 2◦ C. Following this approach. this paper provides an improved and more contextual understanding of the extent of the mitigation challenge specifically and the adaptation challenge more generally. p. [14]). In the absence of such quantification. The second explores the implications of incorporating all greenhouse gases within the scenario pathways for a similar chance of exceeding 2◦ C. China) and regions such as sub-Saharan Africa. temperature. stating ‘we should limit climate change to a maximum of two degrees’ [18] (emphasis added). if not a zero probability of exceeding 2◦ C. Phil.

where the relevant policy community (and recent legislation) align themselves closely with the science of climate change.21]). although the UK Government’s framing of its climate change legislation is the first to detail emission pathways.e. not between acceptable and dangerous climate change. 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. 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. 7 Typically 2050 but also. Nevertheless.6 In part this reflects the continued dominance of ‘end point’ targets7 rather than scientifically credible cumulative emission budgets and their accompanying emission pathways. at least collectively.org on December 27. more recently. ceteris paribus. 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. 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. it is reasonable to describe the UK’s budget as correlating with a 63 per cent chance of exceeding 2◦ C. A (2011) . the disjuncture remains. do not exceed their apportioned emissions budgets. it is reasonable to assume. at their highest 5–33% of exceeding 2◦ C). 5 Or at least the rate of increase associated with a 2◦ C rise by 2100. Phil. it is still far removed from its and others’ high-level commitments to ‘limit climate change to a maximum of two degrees’ [18]. R. the IPCC categorizes a 33 per cent probability of missing or exceeding something as ‘unlikely’. 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. Consequently. and even a highly conservative judgement would suggest the statements represent no more than a 5–33% chance of exceeding 2◦ C. 2010 Beyond dangerous climate change 23 statements all clearly imply very low probabilities of exceeding 2◦ C.g. However. Downloaded from rsta. 2020. Given the UK budget is premised on the CCC’s choice of regime for apportioning global emissions between nations. 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. 4 At the ‘less likely’ end of the spectrum. in which case the importance of low probabilities of exceeding 2◦ C increases substantially. 21]. albeit with the important caveat that other nations. but between dangerous and ‘extremely dangerous’ climate change. 10 per cent as ‘very unlikely’. the report proceeds to describe an emissions pathway out to 2050. Trans. that 2◦ C now represents a threshold. However. the argument for low probabilities is reinforced still further. [20. p. 6 Although this paper explicitly steers away from issues of governance.8 a position that cannot be reconciled with the probabilities implied repeatedly by Government statements (i. 5 per cent as ‘extremely unlikely’ and 1 per cent as ‘exceptionally unlikely’. 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. even within nations such as the UK. the accompanying policies or absence of policies demonstrate a pivotal disjuncture between high level aspirations and the policy reality. acknowledging explicitly the need to re-align policy with cumulative emissions rather than simplistic targets.4 If government responses to climate change are to be evidence-based or at least informed significantly by science.royalsocietypublishing. Complementing the UK’s 2050 emission-reduction target with short-term budgets. Soc.

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

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

The latter. R. 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.13 (ii) The basket of six regime (B6) and twenty-first century budgets The B6 regime. Trans. These emissions are typically related to agriculture and food production. (b) Empirical data The continued and high level of current emissions is consuming the twenty- first century emission budget at a rapid rate. it is necessary to use up-to-date and complete emissions data to construct future emission pathways.14 Moreover. are taken directly from Macintosh [3]. 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.’s PRIMAP tool for estimating probabilities of exceeding 2◦ C [28]. 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]. Consequently. 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. 15 Refers to the lowest level of annual emissions considered viable in the scenario. but it more appropriately captures the contextual implications of alternative emission scenario pathways. 14 ‘Twenty-first century low-emission’ scenarios are premised on low fossil fuel combustion and low deforestation rates.royalsocietypublishing. 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 low- emission scenario pathways [10]. Evidently. 12 For more details see Macintosh [3]. 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.org on December 27. Bows The two remaining budgets. Soc.’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. 2010 26 K. However. the CO2 e regime is not as scientifically robust as the CO2 -only regime. Within this paper data are aggregated for the latest year available from a number of different sources. A (2011) . used previously by Anderson & Bows [2]. Currently Meinshausen’s et al. 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. Anderson and A. 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.’s [7] model assumptions can be calculated using the PRIMAP tool [28] if the 2000–2049 emissions are known. Phil. Downloaded from rsta. 1578 GtCO2 (430 GtC) and 1321 GtCO2 (360 GtC). 13 Probabilities based on Meinshausen et al.

org on December 27. The nationally constructed data from this source exclude CO2 emissions from international aviation and shipping. 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. 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. 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. an assumption is taken that shipping activity is directly proportional to each nation’s proportion of global GDP. 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]. Instead. Trans. For 2006 and 2007. For international marine bunkers. However. the data are not disaggregated into national statistics.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]. the data have previously been subject to high levels of uncertainty [34–36].royalsocietypublishing. division of emissions between Annex 1 and non-Annex 1 nations. These data provide a figure for the global aggregated CO2 and other greenhouse gas emissions between 1990 and 2007. This crude method of apportionment was used previously (e. though inevitably coarse-level.g. Downloaded from rsta. a recent study by the International Maritime Organisation [37] has produced a time series for greenhouse gas emissions associated with international shipping activity. A (2011) .39]. (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]. 2010 Beyond dangerous climate change 27 (i) Energy and industrial process emissions For energy and process related CO2 emissions from 2000 until 2008. However. data are taken from an interpolation between the 2005 and 2010 EPA projections. is also used here as an adequate. [36]). and given difficulties in apportioning international shipping emissions to nations [38. Phil. 16 Ahybrid approach for apportioning aviation emissions between regions may provide insights into potential apportionment regimes for shipping [40]. R. international aviation CO2 for Annex 1 nations is taken from the memo submissions to the United Nations Framework Convention on Climate Change (UNFCCC) [32]. To include these additional emissions. 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]. Soc. To estimate the proportion of international shipping CO2 emissions split between Annex 1 and non-Annex 1 nations.

Soc. — Decide on a global cumulative CO2 and greenhouse gas emission budget associated with a range of probabilities of exceeding 2◦ C.royalsocietypublishing. Phil. after which they grow at 2 per cent in 2010. R. if the rate of growth halves for Annex 1 CO2 emissions. 4. Given the international marine bunker figures are based on proportions of global GDP. Trans. data were not available for either 2008–2010 bunker fuel emissions or 2009–2010 domestic fossil fuel CO2 emissions. the 2010 growth figure is assumed to be half the recent decade’s average (i. However.5 per cent decline in emissions in 2009. again half the recent decade’s average. remaining static in 2009 and 2010. Non-Annex 1 nations are assumed to exhibit 0. fossil fuel CO2 (excluding bunkers) is assumed to decline by 6 per cent in 2009.7%). stabilizing at 0 per cent in 2010. Scenario pathway development Following a brief explanation of how historical and deforestation emissions are accounted for.5 per cent in 2010. Given the absence of recent data from the EPA. Annex 1 and non-Annex 1 non-CO2 greenhouse gas emissions are assumed to proportionally follow the percentage change in their CO2 counterparts. it is assumed that their growth is also impacted by the economic downturn. — Construct emission pathways for the Annex 1 nations for which the cumulative emissions. the construction of the scenario pathways involves the following steps. growth in global fossil fuel CO2 (excluding bunkers) is assumed to be −3. For the emissions of non-CO2 greenhouse gases. non-CO2 greenhouse gas emission growth rates are typically lower than those for global fossil fuel CO2 by approximately 1–2% per year. 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. then the rate of growth for non-CO2 greenhouse gas emissions is also assumed to halve. In the absence of such data. In other words. 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. Although the crisis is beginning to show within 2008 emissions inventories. Anderson and A. it is estimated Annex 1 nations’ emissions declined by 2 per cent in 2008. — Construct emission pathways for the non-Annex 1 nations with varying peak dates.e. Non-Annex 1 nation aviation bunkers are assumed to be stable at 2007 levels until 2009. 2010 28 K. but given China is already reporting high levels of growth for early 2010. Downloaded from rsta. (c) Economic downturn The economic downturn of 2007–2009 had a direct impact on greenhouse gas emission growth rates.0 per cent in 2009 rising to 1. when added to non-Annex 1 and deforestation emissions. do not exceed the global ‘2◦ C’ cumulative budget. particularly those associated with energy. 2. For international aviation bunkers.org on December 27. For Annex 1 nations. estimates draw on the work of Macintosh [3] and the Global Carbon Project [41]. A (2011) . Consequently.

However. 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.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. Whilst such an outcome may have some moral legitimacy. 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. the approach adopted for this paper in which historical (and deforestation) emissions are taken to be global overheads. R. Soc. Such an approach could be argued to unreasonably favour non-Annex 1 nations as deforestation emissions occur within their geographical boundaries. errs in favour of the Annex 1 nations. 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. based on the equity principle. only data for fossil fuel combustion. industrial processes and agriculture are split between Annex 1 and non-Annex 1.19 (b) Deforestation emissions To explore the constraints on emissions from Annex 1 nations of continued growth in emissions from non-Annex 1 nations. Deforestation emissions are treated as a global overhead and thus removed from the available emission budgets prior to developing the pathways. given most Annex 1 countries have already deforested (emitting CO2 ) it could 17 Factoring 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’. 18 Emissions not attributable to any specific geographical location. However. Downloaded from rsta. it evidently would not provide for a politically consensual framing of emission apportionment. While the following analysis focuses specifically on the period 2000–2100. Building on this cumulative emissions per capita approach. Trans. As it stands. it is important to reflect briefly on the treatment of recent historical emissions.royalsocietypublishing. 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. 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. — Construct emission pathways for the Annex 1 nations with a 2015 peak date and ‘orthodox’ annual emission-reduction rates following the peak. However. — Assess the potential future climate impact of these more ‘politically acceptable’ and ‘economic feasible’ pathways. A (2011) . reflected through cumulative emissions per capita’.18 is a pragmatic decision that.org on December 27. 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. Phil. (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. if anything. Given temperature correlates with cumulative emissions of greenhouse gases.

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

Annex 1. For (b) B6 2. this scenario pathway is not compatible with the lower of the cumulative carbon budgets. red line. (a) 50 (b) 40 GtCO2e yr–1 30 20 10 0 2000 2020 2040 2060 2080 2100 2000 2020 2040 2060 2080 2100 year year Figure 3. red line. [7. 2010 Beyond dangerous climate change 31 (a) 50 (b) (c) 40 GtCO2 yr–1 30 20 10 0 2000 2020 2040 2060 2080 2100 2000 2020 2040 2060 2080 2100 2000 2020 2040 2060 2080 2100 year year year Figure 2. 1990 levels by 2020 and then reduce them to 76 per cent below 1990 levels by 2050.28] this scenario pathway is estimated to have a 36 per cent20 probability of exceeding 2◦ C. owing to differences in the 2000–2049 emissions. dotted line. Annex 1. non-Annex 1 nations use the entire carbon budget and leave no emission budget for Annex 1 nations. Soc. Here. probabilities may vary slightly for the same twenty-first century budget. Trans. Thus. Following the same approach. the cumulative twenty-first century CO2 e budget is 2202 GtCO2 e (blue line. (c) C+6) are for the same cumulative twenty-first century CO2 budget of 1578 GtCO2 (blue line. ‘best estimates’ are presented. total including deforestation). R. Downloaded from rsta. CO2 scenarios for approximately 50% chance of not exceeding 2◦ C. global including deforestation).royalsocietypublishing. 21 Given it is not possible to have an immediate cessation of emissions from all Annex 1 nations. Using the PRIMAP tool developed by Meinshausen et al. (b) C+5. All scenario pathways ((a) C+4.org on December 27. However. non-Annex 1.21 20 PRIMAP provides a range of probabilities and a ‘best estimate’ using cumulative emissions between 2000 and 2049. if this is the case. C+2 has non-Annex 1 emissions continuing to grow at a lower than pre-economic downturn rate until 2020 (3% per year). non-Annex 1. Kyoto gas scenarios for approximately 39–48% chance of not exceeding 2◦ C ((a) B6 1 not viable). and peak in 2025. dotted line. A (2011) . Phil.

R. keep total greenhouse gas emissions within the chosen budget.2 billion global population (based on UN Phil. 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]. (d) Basket of six scenario pathways (B6) In a similar approach to the C+ pathways. Given this. 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. Anderson and A. Following the dip in emissions owing to the economic downturn. in this case. Bows To explore the potential of providing for more acceptable reduction rates while still offering a ‘reasonable’ chance of not exceeding 2◦ C. C+5 again uses the higher budget within Macintosh [3] but assumes non- Annex 1 emissions to continue to grow at 4 per cent per year rates until 2020. In addition to considering the effect of non-CO2 greenhouse gases contributing to the overall budget. global emissions are broadly flat between 2014 and 2022. at 4–5% per year for non-Annex 1 nations following the peak date. Global emissions thus peak in 2019 with Annex 1 emissions 6 per cent below 1990 by 2020 and 84 per cent by 2050. C+5 has a 52 per cent chance of exceeding 2◦ C. C+3 assumes non- Annex 1 nations’ emissions grow at a much reduced rate (1% per year) until 2025. and peak in 2025 with a rapid decline to a maximum of 7–8% per year. Soc. and as a result of a step-change in emission growth from non-Annex 1 nations. although emissions are highest in 2020. 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. and if Annex 1 emissions begin to reduce immediately (as in C+1). C+6 uses the same higher budget but illustrates that if reductions are lower. Global emissions are 67 per cent below 1990 by 2050. Within this scenario pathway. The Annex 1 nations have more room to grow in early years than in C+1. 2010 32 K. but are assumed to reach a peak by 2015. Trans. 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 next three scenario pathways (figure 2) use the higher budget of 1578 GtCO2 within Macintosh [3].royalsocietypublishing. 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. This scenario pathway has an estimated 50 per cent chance of exceeding 2◦ C according to PRIMAP [28]. global emissions peak in 2011 and Annex 1 nations’ future emissions do not grow any higher than current levels.org on December 27. 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. in addition to an immediate Annex 1 reduction. C+4 assumes non-Annex 1 nation emissions grow at 4 per cent per year until 2015 peaking in 2020. Annex 1’s emissions peak by 2010 and decline at 7–8% per year. This plausible but highly unlikely scenario has a 37 per cent chance of exceeding 2◦ C according to PRIMAP [28]. A (2011) . To remain within budget. no emission space is available for Annex 1 nations.

1 GtCO2 e.67 tCO2 e per person from 2050 onwards for food-related non- CO2 greenhouse gases compared with an approximate figure of 0. (b) B6 4). 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 pre- economic downturn rates and peak by 2020 (figure 3). This is in line with the value chosen by the UK [8] and results in an estimated 0. total including deforestation. and 1.9 billion people in non- Annex 1 nations. The PRIMAP tool to estimate the probability of exceeding the 2◦ C threshold assumes the vast majority of emissions are released pre-2050 (fig. while Annex 1 nation emissions decline from 2010 onwards. The cumulative twenty-first century CO2 e budget is 2202 GtCO2 e. Annex 1. Trans. 2010 Beyond dangerous climate change 33 (a) 50 (b) 40 GtCO2e yr–1 30 20 10 0 2000 2020 2040 2060 2080 2100 2000 2020 2040 2060 2080 2100 year year Figure 4.95 GtCO2 e per person for 2010 [44.1 GtCO2 e as a minimum annual greenhouse gas emission for non-Annex 1 nations and 0. median estimate for 2050 [46]). this scenario pathway is not viable. and assuming food consumption is more evenly balanced between Annex 1 and non-Annex 1 nations than currently. Soc. Given the food-related non- CO2 greenhouse gases post-2050. 2 in [7]).royalsocietypublishing. 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. Given that within the B6 scenario pathways there is a substantial cumulative emission total for the post- 2050 emissions (with at least 300 GtCO2 e from greenhouse gases associated with Phil.86 GtCO2 e per year for Annex 1 nations. where non-Annex 1 emissions peak in 2020.46].org on December 27. A (2011) . B6 2 makes identical assumptions to B6 1 but for the ‘high’ IPCC emission budget (figure 3). non-Annex 1. In other words.5 GtCO2 e per year. Kyoto gas scenarios for approximately 38–48% chance of not exceeding 2◦ C ((a) B6 3. The additional space allowed leads to a viable scenario pathway. Assuming by 2050 there are 7. emissions from 2017 onwards for non-Annex 1 nations must tend immediately towards the emissions floor of 5. Blue line. dotted line.3 billion in Annex 1 nations [46]. red line. 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. R. In an update to the previous Anderson & Bows [2] study. Emission reductions for non-Annex 1 nations in this case are 6 per cent per year. this would allow approximately 5. Downloaded from rsta.

whereas for Annex 1 nations.22 — N2 O and methane each account for approximately 50 per cent of the non- CO2 greenhouse gases post-2050 (Smith. 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. inputting the 2000–2049 cumulative total for each B6 scenario into PRIMAP will result in an underestimate of the probability of exceeding 2◦ C. B6 3 has the same probability of exceeding 2◦ C as B6 2. figure is in brackets). — 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. peaking in 2030. Both B6 3 and B6 4 take the IPCC’s ‘high’ cumulative budget as a constraint.org on December 27. The emission reductions post-peak for non-Annex 1 nations are 4–5% per year. Bows food production). — Thus 150 GtCO2 e of cumulative emissions are added to the pre-2050 emissions to estimate an alternative probability. pathways are constructed that assume non-Annex 1 nations’ emissions continue to develop along their current trajectory until 2025. (e) Orthodox scenario pathways The final scenario pathways developed are unconstrained by a particular emission budget (figure 5). Trans. with considerably slower growth of 1 per cent per year until a peak date in 2025 (figure 4). an alternative probability is calculated assuming the following. personal communication). emissions decrease at 6 per cent per year. More gradual reductions in emissions from non-Annex 1 nations would render this scenario pathway impossible. Downloaded from rsta. If 150 GtCO2 e is added to the cumulative emission total for each scenario. following a levelling off of emissions until 2014. With steep emission reductions for non-Annex 1 nations post-peak of 6 per cent per year. This scenario pathway has at least a 38 per cent probability of exceeding 2◦ C.royalsocietypublishing. A (2011) . B6 2 has at least a 39 per cent chance of exceeding 2◦ C and is potentially as high as 48 per cent. B6 4 mirrors the assumptions within C+3. PRIMAP estimates an approximate ten percentage point increase in probability of exceeding 2◦ C (see table 1. For example. Soc. then reducing at 22 Thisis 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. 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). Phil. Anderson and A. R. and potentially as high as 47 per cent once post-2050 emissions are factored in. To account for this underestimate. 2010 34 K. For both the C+ and B6 regimes. — The shorter-lived nature of methane compared with N2 O results in a negligible impact on post-2050 warming from methane.

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

Phil. 5. non-Annex 1. Discussion (a) CO2 plus (C+) Although six C+ pathways were developed in the previous section. 2. 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). Emission scenarios for approximately 88–92% chance of not exceeding 2◦ C. 201–204]. 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.5 per cent per year from all sources. For orthodox C+. Stern concludes ‘it is likely to be difficult to reduce emissions faster than around 3 per cent per year’ [6. emissions are assumed to be relatively stable with a peak in 2016 and subsequent emission reductions of 3 per cent per year. Furthermore. has post-peak emissions reducing at 3. Figures in excess of 3500 GtCO2 e can be assumed to be closer to the 750 ppmv range.royalsocietypublishing. a rate considered politically and economically acceptable23 (3% reduction per year).org on December 27. Bows (a) (b) 60 GtCO2e yr–1 40 20 0 2000 2020 2040 2060 2080 2100 2000 2020 2040 2060 2080 2100 year year Figure 5. For the Annex 1 nations. pp. red line. Soc. 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. Cumulative emissions of approximately 2700 GtCO2 are associated with stabilization of 550 ppmv CO2 . R. Annex 1. These scenario pathways both result in an 88 per cent chance of exceeding the 2◦ C threshold (potentially 92% for orthodox B6). Orthodox B6 has cumulative emissions of greenhouse gases of 3662 GtCO2 e. One exceeded the lower of the two chosen 23 The pathway of the CCC’s [8] most challenging scenario. thus a reasonable probability of exceeding 4◦ C. 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’. 32]. dotted line. Blue line. Anderson and A. total including deforestation. ‘2016:4% low’. 2010 36 K. A (2011) . cumulative emissions of CO2 alone are 2. p. two were rejected for exceeding the constraints on cumulative CO2 budgets related to the 2◦ C temperature threshold.741 GtCO2 . Downloaded from rsta.

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

For example. while still within the bounds of possibility of not exceeding the 2◦ C threshold (8–12% chance).25 However. Phil. Soc. Downloaded from rsta. Aside from the considerable bio-energy debate surrounding the sustainability of biofuels. 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). 25 Bottom-up and built on typically idealized inputs with only limited regard for ‘real-world’ constraints. recent overviews of scenarios generated by a range of different international integrated assessment modelling communities [10. it is perhaps surprising they are central to so many scenarios. Whilst sufficient uranium exists for moderate increases in conventionally fuelled reactors. the two orthodox scenario pathways paint a picture of ongoing non- Annex 1 emission growth. included as a ‘key energy supply technology’ in all but one of the 450ppmv scenarios reviewed. yet were without detailed analysis of potentially significant constraints on storage capacity. A (2011) . deforestation. are more closely aligned with much higher climate change futures associated with at least 3–4◦ C of warming. the outputs are typically removed from the political and empirical reality within which responses to climate change are developed. (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. To explore the implications of this. 2010 38 K. the overarching data and trend lines underpinning Köne and Büke’s analysis were available at the time many of the scenarios were developed.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. energy and industrial processes.royalsocietypublishing. Bows probable that non-Annex 1 nations will set targets based on levels of carbon or energy intensity improvements. These bio-CCS scenarios all included wider CCS facilities. and then sustained emission reductions at rates considered politically and economically feasible.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. R. Given the many unknowns around bio-CCS. Of the principal 450 ppmv scenarios reviewed. slow action to mitigate emissions on the part of Annex 1 nations. here too the integrated assessment modelling approach typically treats these wider concerns as exogenous and resolvable. this despite irrefutable evidence to the contrary [48]. Anderson and A. Resulting cumulative emissions. 27 The inclusion of bio-CCS also demonstrates a degree of non-contextual engagement with technology.org on December 27. Although these will go some way towards addressing future high-carbon lock-in. 26 While Köne & Büke’s [48] paper was published after many of the scenarios referred to.14] illustrate the non-contextual framing that typifies much of this form of analysis. while it may be argued that the latter approach benefits from greater internal consistency and more theoretically coherent parameters. it is unlikely that emission growth rates will be significantly moderated during the coming decade. significant ramping up of nuclear capacity is likely to require fast breeder reactors with major challenges associated with their widespread introduction. Trans. the majority had a global emissions peak in 2010. This non-contextual approach to technology extends to nuclear power.

Phil. 6. Soc. on closer investigation. if they exist at all. despite the actual date being around 2006. A (2011) . (e) Development on the authors’ 2008 paper Two years on from earlier analysis by Anderson & Bows [2]. 29 Within the integrated assessment modelling scenarios referred to. Downloaded from rsta. allied with their inevitable opaqueness and often abstract and implicit assumptions.g. but can also provide ‘contextual’ parameters and constraints to more complex modelling approaches. the conclusions arising from this paper are significantly bleaker than those of the authors’ 2008 paper. Furthermore. 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. leaves space for the simpler. However. disaggregating global into Annex 1 and non- Annex 1 emission pathways only serves to exacerbate the scale of this disjuncture between the rhetoric and reality of mitigation.29 The non-contextual framing of many complex modelling approaches (including integrated assessment modelling).org on December 27. Conclusions Over the past five years a wealth of analyses have described very different responses to what. 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. 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. For all practical purposes aggregated emissions related to Annex 1 are the same as those for Annex B. (1) What delineates dangerous from acceptable climate change? (2) What risk of entering dangerous climate change is acceptable? (3) When is it reasonable to assume global emissions will peak? (4) What reduction rates in post-peak emissions is it reasonable to consider? (5) 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. the division related to Annex B regions.royalsocietypublishing. are increasingly slim. at first sight. In both these regards and with the continued high-level reluctance to face the real scale and urgency of the mitigation challenge. 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]. only the global economic slump has had any significant impact in reversing the trend of rising emissions. more transparent and contextual approach to scenarios presented in this paper. the prospects for avoiding dangerous climate change. R. [49. Trans.50]). appears to be the same question: what emission- reduction profiles are compatible with avoiding ‘dangerous’ climate change? However.

Phil. those providing policy advice frequently take a much less categorical position.org on December 27. Soc. A (2011) . Bows While (1) and.31 there is little political appetite and limited academic support for such a revision. in effect. 2010 40 K. can be understood in relation to Annex 1 and non-Annex 1 emission profiles. 160]. For example. Trans. 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. Within global emission scenarios.royalsocietypublishing. Despite such clarity. In stark contrast. R. Nevertheless. although the implications of their more nuanced analyses are rarely communicated adequately to policy makers.30 the latter three have pivotal regional dimensions that. However. and despite the evident logic for revising the 2◦ C threshold. Downloaded from rsta. 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. 30 Regions can evidently identify what may constitute dangerous within their geographical boundaries. However. Moreover. the recent reassessment of these impacts upwards suggests current analyses of mitigation significantly underestimate what is necessary to avoid dangerous climate change [20. to a lesser extent. most policy advice is to accept a high probability of extremely dangerous climate change rather than propose radical and immediate emission reductions. given that it is a ‘political’ interpretation of the severity of impacts that informs where the threshold between acceptable and dangerous climate change resides. such as those developed by Stern [6]. p.32 Put bluntly. 33 With policies themselves lagging even further behind in terms of both actual reductions achieved or planned for. the Copenhagen Accord and many other high- level 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. 31 If the impacts are to remain the principal determinant of what constitutes dangerous.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. the CCC are. 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. the CCC [8] and ADAM [47]. (2) are issues for international consideration.21]. conceding that avoiding dangerous (and even extremely dangerous) climate change is no longer compatible with economic prosperity. Anderson and A. 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. while the rhetoric of policy is to reduce emissions in line with avoiding dangerous climate change. In relation to the first two issues. 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. on closer examination these analyses suggest such reduction rates are no longer sufficient to avoid dangerous climate change. at their most crude level. 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.

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

Edmonds. V.034) 4 Shell. S64–S81. L. D.1016/j. J. Copenhagen. R. P. Phil. H. 10 Clarke. Norwich. Similar thanks go to Steve Sorrel. Tignor. DC: US Department of Energy. London. Averyt.06. 2 Anderson.enpol. 2009 Copenhagen: in the balance press briefing.. M. S.1016/j. Tyndall Centre briefing note 40. L. L. Anderson and A.. A 366. Grateful thanks go to the following Tyndall Centre. Norwich.. H. UK: The Stationery Office. L. 2009 FCCC/CP/2009/L. N. Sustainable Consumption Institute and Manchester Alumni researchers: Rudra Shrestha.eneco.. (doi:10. Belgium: European Commission.1098/rsta. Frieler. J. Meinshausen. 2010 42 K. M.. Raper.. B. M. Hare. R.enpol. Dan Calverley and Richard Starkey. & Ritchie.. (eds) 2007 Contribution of working group 1 to the fourth assessment report of the Intergovernmental Panel on Climate Change. D.. S. S. M. A (2011) . UK: Foreign Office and Department for Energy and Climate Change. Z. J. Starkey. 7 Meinshausen. The Netherlands: Shell International BV. R. Paris. Agnolucci. Knutti. Richels.01. Denmark: United Nations Climate Change Conference. S. Shackley. 31. 5 IEA. 14 Clarke. L. Energy Econ. R. Colyer.. Edmonds. & Bows. This paper is intended as a small contribution to such a vision and future of hope. France: International Energy Agency. Soc. Bachir Ismael Ouedraogo. & Allen. 2009 International climate policy architectures: overview of the EMF 22 international scenarios. S. H.0138) 3 Macintosh.2009. A. 2009 Defining dangerous climate change—a call for consistency.2008. & Millier. & Tavoni... J. senior fellow of the Sussex Energy Group at the University of Sussex. Washington. Bows and dispassionate assessment of the scale of the challenge faced by the global community.. H. Bows.7.. UK: University of East Anglia. 2009 Adaptation and mitigation strategies: supporting European climate policy. K. 2007 Scenarios of greenhouse gas emissions and atmospheric concentrations. M. (doi:10.. C.. & Ekins.. 2009 World energy outlook. & Miliband. Trans. K. 3863–3882.. NY: Cambridge University Press. Jacoby. Dhar. & Bows. Neufeldt. R. N. K.. (doi:10. R. Brussels.1016/j. UK: Department of Energy and Climate Change. 17 DECC. R. H.. Cambridge. Qin. New York.. Krey. S. 2006 Stern review on the economics of climate change. 2010 Keeping warming within the 2◦ C limit after Copenhagen. 9 Hulme. 2009 The UK low carbon transition plan: national strategy for climate and energy. A. 2008 Reframing the climate change challenge in light of post-2000 emission trends..002) 12 Wang. Rose. Soc. J. M. 1158–1162. T. 2008 Low-carbon society scenarios for India. A. 2008 The Tyndall decarbonisation scenarios—part II: scenarios for a 60% CO2 reduction in the UK. E. A.2010. The Hague. 16 Anderson. 3764–3773. K. W.royalsocietypublishing. Downloaded from rsta. M. UK. 18 Miliband. & Richels. London. Energy Policy 38. Nature 458. 2964–2975. K. Frame. for their assistance and valuable comments in relation to this research. 19 Solomon. (doi:10. D. M. R. D. UK: Cambridge University Press.. Mander. 2008 Carbon emission scenarios for China to 2100. References 1 Copenhagen Accord.. Pitcher.2008. S156–S176. & Mahapatra. Reilly. 2008 Building a low-carbon economy—the UK’s contribution to tackling climate change. 13 Sukla.. Maria Sharmina.1038/nature08017) 8 CCC. & Watson. 2009 Greenhouse-gas emission targets for limiting global warming to 2◦ C. P. Climate Policy 8. (doi:10.org on December 27. 2007 Limiting global climate change to 2 degrees Celsius: the way ahead for 2020 and beyond. 15 European Commission. Chen.. 2008 Shell energy scenarios to 2050. all of whom are based at the University of Manchester. Tyndall Centre working paper 121. Phil. A. 6 Stern. Energy Policy 36. Marquis.013) 11 Anderson. Manning. Trans.. P.. Cambridge.10.

H. New York. (doi:10.1016/j.. 31 Eyring. 28 PRIMAP. A (2011) .. Gigilo. A. & Meinshausen. L. 2009 Carbon budget and trends 2008.1073/pnas. H. Geophys. org/carbonbudget.enpol. 2006 Living within a carbon budget. D. In press. Anderson. R. 39 Gilbert. Potsdam. S. 298–313. 1999 The annual net flux of carbon to the atmosphere from land use 1850–1990. E.010) 41 Global Carbon Project.. Pachauri. J.2008. USA 106. 2010 Apportioning aviation CO2 emissions to regional administrations for monitoring and target setting. M. R. Sci. et al. (doi:10. France: International Energy Agency. London. & Anderson. Shackley. Paris. UK: University of Manchester.1038/nature08019) 26 Matthews. Transport Policy 17. Biogeosciences 6.1016/j. et al. 43 van der Werf. & Mander. Meinshausen. Tellus B 51B.enpol.. Proc. J. Morton.07. Res. A. UK. (doi:10.1016/ j. H.1029/2003JD003751) 36 Anderson. Nature 912. T. (doi:10. Mander. 829–832. G. 2009 Defining dangerous anthropogenic interference. 2005 Emissions from international shipping: 1.0901303106) 22 New. Bows. D. 3754–3763. 2009 Global CO2 emissions from fossil-fuel burning. Nature 458.003) 24 Bows.. Manchester.. A. Trans. M. 2010 The PRIMAP model. P. 38 Environmental Audit Committee. Environ. S. II and III to the fourth assessment report of the Intergovernmental Panel on Climate Change. 2010 GHG data from UNFCCC. 42 Houghton. UK: The Stationery Office. F. & Lauer. J. K. D17305. C. N.1029/2004JD005619) 35 Corbett. 4650. J. R. R. Jones. A. G. 2009 Reducing the CO2 and other emissions from shipping: fourth report of session 2008–2009. Cambridge. UK: Tyndall Centre... 110. 4133–4137.0812355106) 21 Mann.059) 32 UNFCCC.. & Anderson. (doi:10. M. K. 40 Wood. P. J. R. Starkey.5194/bg-6-235-2009) Phil.atmosenv. Manchester. Kohler. Geophys. (doi:10.1038/ climate. Frame.06. J. 1163–1166. R..2009. 2010 Beyond dangerous climate change 43 20 Smith. D. Transport impacts on atmosphere and climate: shipping. (doi:10. 2009 The proportionality of global warming to cumulative carbon emissions. UK: Potsdam Institute for Climate Impact Research. (doi:10.2010.. P. Bleda. Soc. 2009 Estimates of fire emissions from an active deforestation region in the southern Amazon based on satellite data and biogeochemical modelling. Natl Acad.. Gillett. van Aardenne. Oak Ridge. J. J. Randerson. Stott. Atmos. A. (eds) 2007 Contribution of working groups I. NY: United Nations. 143–144. A. 2009 Warming caused by cumulative carbon emissions towards the trillionth tonne. 2003 Updated emissions from ocean shipping. G. Proc. New York. V.royalsocietypublishing. Bows. 2008 The Tyndall decarbonisation scenarios—part I: development of a backcasting methodology with stakeholder participation. TN: Oak Ridge National Laboratory. Energy Policy 36. L. Cambridge. Lowe. Sci. 2008 The Garnaut climate change review. 4065–4066. 3714–3722. 2008. The last 50 years.1073/pnas. R.. R.globalcarbonproject. & Anderson.. Bows. S. R. L.. T. S. & Andres.126) 23 Mander. K. 235–249. Nature 459.. 2009 CO2 emissions from fuel combustion. W. & Ekins. B. D.. 34 Eyring. M. M. P.2009. 2009 Mind the gap. A.003) 37 Buhaug. N. 206–215. cement manufacture.. O. 2008 From long-term targets to cumulative emission pathways: reframing UK climate policy. USA 106. W. & Starkey. See www. J. K. DeFries. (doi:10. Bows.. 30 Boden. & Reisenger... P.. 108. Liverman. 2010 Shipping and climate change: scope for unilateral action. UK: Cambridge University Press. (doi:10.01. R. (doi:10. S. & Zickfeld. (doi:10... K.1016/j.04. Energy Policy 36. 2009 2nd IMO GHG study.. & Kohler. 33 IEA.1038/nature08047) 27 Garnaut. Huntingford. J. Downloaded from rsta. Marland. A.org on December 27. and gas flaring: 1751–2006. 2009 Assessing dangerous climate change through an update of the Intergovernmental Panel on Climate Change (IPCC) ‘reasons for concern’. Natl Acad. Collatz.. Agnolucci. NY: Cambridge University Press. A. K. London. V. UK: International Maritime Organisation. S. A. D. R. K. 25 Allen. et al. 29 IPCC. Res. P. & Kasibhatla.tranpol. C. C.

(doi:10. Renew. Sustainable Energy Rev. Planet. Office of Atmospheric Programs. 2010 44 K.. Bows 44 EPA. 2006 Global anthropogenic non-CO2 greenhouse gas emissions: 1990–2020. 48 Köne. K. Fei. Anderson and A.2008. & Bin.002) 50 Schneider. A. (doi:10.gloplacha. Downloaded from rsta. T. Climate Change Division. 2906–2915. Ç. 15 728–15 735.un. 2009 The use of economic analysis in climate change appraisal of post-2012 climate policy. See esa.. & Büke. H. T. D. S. 45 Jiankun. 46 UN. Wenying.006) 49 Nusbaumer. China: Tsinghua University. 47 Hof. 2010. 164–172. Forecasting of CO2 emissions from fuel combustion using trend analysis.org on December 27. Soc.1016/j. USA 102. Proc. A.0506356102) Phil. Sci. Bilthoven. D. Glob.rser. 2005 Probabilistic assessment of ‘dangerous’ climate change and emissions pathways.1016/j. 2009 Long-term climate change mitigation target and carbon permit allocation. G. The Netherlands: Netherlands Environmental Assessment Agency. 14. Natl Acad. H. R. & Mastrandrea. 2008 Climate and carbon cycle changes under the overshoot scenario. Trans. L. M. (doi:10. Change 62.royalsocietypublishing. Beijing. M.2010. & Matsumoto. J.1073/ pnas.org/UNPP. US Environmental Protection Agency.. C. 2010 UN Population Division’s annual estimates and projections. den Elzen. & van Vuuren. A (2011) . J.01.06.