Four degrees and beyond: the potential for a global ... - Amper

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38 K. Anderson and A. Bows probable that non-Annex 1 nations will set targets based on levels of carbon or energy intensity improvements. Although these will go some way towards addressing future high-carbon lock-in, it is unlikely that emission growth rates will be significantly moderated during the coming decade. To explore the implications of this, the two orthodox scenario pathways paint a picture of ongoing non- Annex 1 emission growth, slow action to mitigate emissions on the part of Annex 1 nations, and then sustained emission reductions at rates considered politically and economically feasible. Resulting cumulative emissions, while still within the bounds of possibility of not exceeding the 2 ◦ C threshold (8–12% chance), are more closely aligned with much higher climate change futures associated with at least 3–4 ◦ C of warming. (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. 25 However, while it may be argued that the latter approach benefits from greater internal consistency and more theoretically coherent parameters, the outputs are typically removed from the political and empirical reality within which responses to climate change are developed. For example, recent overviews of scenarios generated by a range of different international integrated assessment modelling communities [10,14] illustrate the non-contextual framing that typifies much of this form of analysis. Of the principal 450 ppmv scenarios reviewed, the majority had a global emissions peak in 2010, this despite irrefutable evidence to the contrary [48]. 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. These bio-CCS scenarios all included wider CCS facilities, yet were without detailed analysis of potentially significant constraints on storage capacity. 27 At least half of the scenarios relied on significant levels of ‘overshoot’ (between 500 and 590 ppmv CO2e) 28 and 24Though constrained explicitly to consider top-down emissions only with coarse high-level divisions between food, deforestation, energy and industrial processes. 25Bottom-up and built on typically idealized inputs with only limited regard for ‘real-world’ constraints. 26While Köne & Büke’s [48] paper was published after many of the scenarios referred to, the overarching data and trend lines underpinning Köne and Büke’s analysis were available at the time many of the scenarios were developed. 27The inclusion of bio-CCS also demonstrates a degree of non-contextual engagement with technology. 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). Given the many unknowns around bio-CCS, it is perhaps surprising they are central to so many scenarios. This non-contextual approach to technology extends to nuclear power, included as a ‘key energy supply technology’ in all but one of the 450ppmv scenarios reviewed. Whilst sufficient uranium exists for moderate increases in conventionally fuelled reactors, significant ramping up of nuclear capacity is likely to require fast breeder reactors with major challenges associated with their widespread introduction; here too the integrated assessment modelling approach typically treats these wider concerns as exogenous and resolvable. Phil. Trans. R. Soc. A (2011) Downloaded from rsta.royalsocietypublishing.org on November 30, 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], despite the actual date being around 2006. 29 The non-contextual framing of many complex modelling approaches (including integrated assessment modelling), allied with their inevitable opaqueness and often abstract and implicit assumptions, leaves space for the simpler, more transparent and contextual approach to scenarios presented in this paper. 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, but can also provide ‘contextual’ parameters and constraints to more complex modelling approaches. (e) Development on the authors’ 2008 paper Two years on from earlier analysis by Anderson & Bows [2], only the global economic slump has had any significant impact in reversing the trend of rising emissions. However, 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 prospects for avoiding dangerous climate change, if they exist at all, are increasingly slim. Furthermore, 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. In both these regards and with the continued high-level reluctance to face the real scale and urgency of the mitigation challenge, the conclusions arising from this paper are significantly bleaker than those of the authors’ 2008 paper. 6. Conclusions Over the past five years a wealth of analyses have described very different responses to what, at first sight, appears to be the same question: what emissionreduction profiles are compatible with avoiding ‘dangerous’ climate change? However, on closer investigation, 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. (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.g. [49,50]). 29 Within the integrated assessment modelling scenarios referred to, the division related to Annex B regions. For all practical purposes aggregated emissions related to Annex 1 are the same as those for Annex B. Phil. Trans. R. Soc. A (2011) Downloaded from rsta.royalsocietypublishing.org on November 30, 2010
Page 1 and 2: ISSN 1364-503X volume 369 number 19
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Page 5 and 6: Editorial David Garner Phil. Trans.
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Water availability in +2 ◦ C and
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(a) number of models, black line nu
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change in run-off (%) change in run
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Agriculture and food systems in sub
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REVIEW Phil. Trans. R. Soc. A (2011
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Review. Interactions in a 4 ◦ C w
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Editorial Editorial 3 D. Garner Pre
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