Beyond ‘dangerous’ climate change: emission scenarios for a new world

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 emission-reduction 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?

While (1) and, to a lesser extent, (2) are issues for international consideration,³⁰ the latter three have pivotal regional dimensions that, at their most crude level, can be understood in relation to Annex 1 and non-Annex 1 emission profiles.

In relation to the first two issues, 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. Despite such clarity, those providing policy advice frequently take a much less categorical position, although the implications of their more nuanced analyses are rarely communicated adequately to policy makers. Moreover, given that it is a ‘political’ interpretation of the severity of impacts that informs where the threshold between acceptable and dangerous climate change resides, the recent reassessment of these impacts upwards suggests current analyses of mitigation significantly underestimate what is necessary to avoid dangerous climate change [20,21]. Nevertheless, and despite the evident logic for revising the 2^°C threshold,³¹ there is little political appetite and limited academic support for such a revision. In stark contrast, 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.³² Put bluntly, while the rhetoric of policy is to reduce emissions in line with avoiding dangerous climate change, most policy advice is to accept a high probability of extremely dangerous climate change rather than propose radical and immediate emission reductions.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. Within global emission scenarios, such as those developed by Stern [6], the CCC [8] and ADAM [47], 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. However, on closer examination these analyses suggest such reduction rates are no longer sufficient to avoid dangerous climate change. For example, 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, p. 160]. However, 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, the CCC are, in effect, conceding that avoiding dangerous (and even extremely dangerous) climate change is no longer compatible with economic prosperity.

In prioritizing such economic prosperity over avoiding extremely dangerous climate change, the CCC, Stern, ADAM and similar analyses suggest they are guided by what is feasible.³⁴ However, 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. All premise their principal analyses and economic assessments on the ‘infeasible’ assumption of global emissions peaking between 2010 and 2016; a profound departure from the more ‘feasible’ assumptions framing the majority of such reports. The scale of this departure is further emphasized when disaggregating global emissions into Annex 1 and non-Annex 1 nations, as the scenario pathways developed within this paper demonstrate.

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, do global emissions peak by 2020. Consequently, the 2010 global peak central to many integrated assessment model scenarios as well as the 2015–2016 date enshrined in the CCC, Stern and ADAM analyses, do not reflect any orthodox ‘feasibility’. By contrast, the logic of such studies suggests (extremely) dangerous climate change can only be avoided if economic growth is exchanged, at least temporarily, for a period of planned austerity within Annex 1 nations³⁶ and a rapid transition away from fossil-fuelled development within non-Annex 1 nations.

The analysis within this paper offers a stark and unremitting assessment of the climate change challenge facing the global community. There is now little to no chance of maintaining the rise in global mean surface temperature at below 2^°C, despite repeated high-level statements to the contrary. Moreover, the impacts associated with 2^°C have been revised upwards (e.g. [20,21]), sufficiently so that 2^°C now more appropriately represents the threshold between dangerous and extremely dangerous climate change. Consequently, and with tentative signs of global emissions returning to their earlier levels of growth, 2010 represents a political tipping point. 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, particularly those directly informing policy.

However, this paper is not intended as a message of futility, 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. Real hope and opportunity, if it is to arise at all, will do so from a raw and dispassionate assessment of the scale of the challenge faced by the global community. This paper is intended as a small contribution to such a vision and future of hope.

Acknowledgements