Beyond 'dangerous' climate change: Emission scenarios for a new world

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. © 2011 The Royal Society.