IPCC working group 1 (on the physical scientific aspects of the climate system and climate change) and working group 2 (on the vulnerability of socio-economic and natural systems to climate change) concluded that Greenhouse gas emissions must be rapidly eliminated if the world is to remain habitable. The fundamental question considered by IPCC working group 3 (on mitigation of climate change) was therefore how to decarbonize the global economy. It considered economic scenarios up to the year 2100 compatible with several representative carbon pathways and assumed continued exponential global economic growth. Depending on the scenario, the global economy by the year 2100 would be as much as ten times larger than today yet be carbon neutral, and at least some scenarios would have temperatures only 2oC above pre-industrial levels. Depending on the scenario, over 90% of the energy would be produced by technologies that do not yet exist. In addition, several of the scenarios place heavy reliance on Carbon Capture and Storage (CCS) even though such technologies are only currently available at very small scales.

Even at current levels of energy consumption, decarbonization will be challenging. The debate it therefore: is continued global exponential growth compatible with a habitable planet?