The 1992 UN Framework Convention on Climate Change (UNFCCC) commits signatories to achieving a “stabilisation of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system”, leaving unspecified the level of global warming that is “dangerous” (Oppenheimer and Petsonk 2005; Liverman 2009). The Intergovernmental Panel on Climate Change (IPCC) assessments have progressively improved the evidence base on the potential impacts of climate change, but large uncertainties remain. These uncertainties, combined with the geographical diversity of impacts, vulnerabilities and adaptive capacities, and lack of clarity around risk tolerance, have made it difficult to arrive at a precise temperature ceiling for avoidance of “dangerous” climate impacts.
The main outcomes of the UNFCCC 16th Conference of the Parties (CoP16) were the Cancun Agreements of 2010 (See Appendix 1 for the relevant text from the Cancun Agreements). In the CoP16 Draft Decision document (UNFCCC 2010), ,4 and 5, the CoP commits to keeping the global mean temperature rise to no higher than 2 degrees Celsius above pre-industrial temperatures, and in ,138 and 139, the CoP also commits to review, between 2013-2015, the adequacy of this goal.
The adoption of this 2 °C target occurred despite increasing evidence that for at least some nations and ecosystems, there is already a risk of severe impacts at 2 °C (Richardson et al. 2009). This is why, on the insistence of some of the more vulnerable State Parties, the Cancun Agreements include a commitment to review this, and consider a lower 1.5°C target.
The Dangerous Climate Change Assessment Project (DanCCAP) has aimed to address the difficulty in defining dangerous climate change by adopting a system-by-system expert elicitation on dangerous climate change impacts on several Earth systems of concern. Scientists who are primary experts on five “systems” – coral reefs, Arctic ecosystems, Arctic permafrost carbon cycling, mountains and ice sheets – were independently surveyed on the risks of climate change to each system1. The risks to individual systems were then combined to create a profile, showing the accumulation of 1 Additional surveys on Amazon tropical forests and sea level rise are currently underway, but had not been completed at the time of writing this final report.
This report summarises the key results from five DanCCAP system surveys, presenting a risk profile showing experts’ estimates of “dangerous climate change” for each system. The report begins with a description of the approach used in the expert elicitation. This is followed by a summary of key results for each system assessed. The report concludes with an aggregate risk profile. The full survey reports for each system are included as Appendices.