ABSTRACT
Climate change is widely held to be the most urgent issue facing humanity. After decades of study and debate, it is now generally accepted that we need to limit the global temperature rise to 2oC in order to avoid the prospect of catastrophic irreversible global warming, with many pushing for a lower target of 1.5oC.1 According to the latest climate science, the two degree target means returning atmospheric greenhouse gas concentrations to 350 parts per million (ppm), though most climate policy is geared towards a target of 450ppm.2 In 2009, concentrations were already at 399ppm.3 To stabilise concentrations at 450ppm, global greenhouse gas emissions must be at least halved from 1990 levels by 2050, meaning that developed countries may need to cut emissions by 85 per cent.4
