Australians need to reduce their per-capita greenhouse gas emissions to 5% of 2000 levels by 2050 if the international community is to stabilize the concentration of atmospheric CO2 at 450 parts per million (ppm) [18]. Since the Garnaut report was published, it has become apparent that 350 ppm is a more realistic target if global warming is to be limited to 2°C. Either target is a huge challenge and will require unprecedented changes to the way we generate and use energy. See Figure 8.1 to get a better idea of the challenge.