Introduction to special topic: Energy pathways to a low-carbon society

Energy and carbon are at the nexus of climate change, environment, health, and socio-economic development. The imperative to move towards cleaner and renewable energy to reduce greenhouse gas is gaining significant public and private sector support. Reducing carbon in the atmosphere has fast emerged as a major means to achieve this, since carbon content can be measured and hence the pathways can be well-defined. The December 2009 Copenhagen Accord recognized "the scientific view that the increase in global temperature should be below 2 degrees Celsius on the basis of equity and in the context of sustainable development." To achieve this goal, the emerging scenario (e.g., the International Energy Agency (IEA) Report: World Energy Outlook 2009) is that the atmospheric concentration of CO₂ be stabilized at around 450 ppm. If global emissions peak in 2015, we estimate that annual reductions in CO ₂ concentration of up to 5% would be necessary, equivalent to the Kyoto Protocol targets. Delaying reductions beyond the 2015 peak, however, would necessitate more drastic reduction rates that would be very difficult to achieve. To reach the necessary annual reduction in either case, investment in nonfossil energy must be significantly increased.