Reframing the climate change challenge in light of post-2000 emission trends

The 2007 Bali conference heard repeated calls for reductions in global greenhouse gas emissions of 50 per cent by 2050 to avoid exceeding the 2°C threshold. While such endpoint targets dominate the policy agenda, they do not, in isolation, have a scientific basis and are likely to lead to dangerously misguided policies. To be scientifically credible, policy must be informed by an understanding of cumulative emissions and associated emission pathways. This analysis considers the implications of the 2°C threshold and a range of post-peak emission reduction rates for global emission pathways and cumulative emission budgets. The paper examines whether empirical estimates of greenhouse gas emissions between 2000 and 2008, a period typically modelled within scenario studies, combined with short-term extrapolations of current emissions trends, significantly constrains the 2000-2100 emission pathways. The paper concludes that it is increasingly unlikely any global agreement will deliver the radical reversal in emission trends required for stabilization at 450ppmv carbon dioxide equivalent (CO2e). Similarly, the current framing of climate change cannot be reconciled with the rates of mitigation necessary to stabilize at 550ppmv CO2e and even an optimistic interpretation suggests stabilization much below 650ppmv CO2e is improbable. © 2008 The Royal Society.