CO2 emission reduction assumptions overly optimistic, says study

Stabilization of atmospheric concentrations of CO₂ and other greenhouse gases was the primary objective of the 1992 United Nations Framework Convention on Climate Change approved by almost all countries, including the United States, said Wigley.

“Stabilization is a more daunting challenge than many realize and requires a radical ‘decarbonization’ of energy systems,” said Wigley. “Global energy demand is projected to grow rapidly, and these huge new demands must be met by largely carbon-neutral energy sources -- sources that either do not use fossil fuels or which capture and store any emitted CO₂.”

Calculations by the Nature authors show that at least two-thirds of the amount of carbon that has to be removed from the energy supply in order to stabilize atmospheric CO₂ concentrations at roughly 500 parts per million is assumed to occur automatically by the IPCC authors. Atmospheric CO₂ levels are currently at about 390 parts per million.

Enormous advances in energy policy in the coming decades will be needed to stabilize atmospheric concentrations of CO₂ at levels currently considered “acceptable,” the Nature authors concluded.

Unlike the IPCC authors, who built in assumptions about future “spontaneous” technological innovations, the Nature commentary authors began with a set of “frozen technology” scenarios as baselines -- scenarios in which energy technologies are assumed to stay at present levels. “With a frozen technology approach, the full scope of the carbon-neutral technology challenge is placed into clear view,” said Green.

“In the end, there is no question whether technological innovation is necessary -- it is,” the authors wrote in Nature. “The question is, to what degree should policy focus explicitly on motivating such innovation? The IPCC plays a risky game in assuming that spontaneous advances in technological innovation will carry most of the burden of achieving future emissions reductions, rather than focusing on those conditions that are necessary and sufficient for those innovations to occur.”