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Assuming the best?

New analysis looks at ­technology advances woven into IPCC scenarios

Renewable energy sources, such as wind, could help society
reduce emissions of carbon dioxide. (Photo by Bob Henson.)

Reducing global emissions of carbon dioxide over the coming century will be more challenging than society has been led to believe, according to a research commentary that appeared on 3 April in Nature.

The authors, from the University of Colorado at Boulder (CU), NCAR, and McGill University, say the Inter­governmental Panel on Climate Change (IPCC) has significantly underestimated the technological challenges of reducing CO2 emissions. The commentary, “Dangerous Assumptions,” concludes that the IPCC is overly optimistic in assuming that, even without action by policy­makers, society will develop and implement new technologies to ­dramatically reduce the growth of future emissions.

Because of rapid economic development, changes in “carbon intensity”—
CO2 emissions per unit of energy ­consumed—already are greater than those predicted by the IPCC, according to CU’s Roger Pielke Jr., lead author of the Nature commentary. In Asia, for instance, the demands of more energy-intensive economies are being met with conventional fossil-fuel technologies, a process expected to continue there for decades and eventually move into Africa.

In estimating the emissions reductions required to stabilize CO2 concentrations, the IPCC divides future emissions changes into those that will occur spontaneously (such as in the absence of climate policies) and those that are policy driven. According to the authors, this division hides the full challenge associated with stabilizing the amount of carbon dioxide in the atmosphere. Co-author Tom Wigley of NCAR notes that stabilizing 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.

Daniel Wildcat
Tom Wigley.
(Photo by Carlye Calvin.)

The Nature commentary points out that to stabilize CO2 levels at around 500 parts per million (compared to the present level of about 390 ppm), the IPCC scenarios assume that 57% to 96% of the total carbon removed from the energy supply over the coming century would occur spontaneously. ”We believe these kinds of assumptions in the analysis blind us to reality and could potentially distort our ability to develop effective policies,” says Pielke.

According to Wigley, “Stabilization is a more daunting challenge than many realize and requires a radical ‘decarbonization’ of energy systems. 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 that capture and store any emitted carbon dioxide.”

Unlike the large future “spontaneous“ technological innovations assumed by the IPCC, the Nature commentary authors began with a set of “frozen technology“ scenarios as baselines—scenarios in which energy-consuming and energy-producing 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,” says McGill’s Christopher Green.

“In the end, our message should be viewed optimistically rather than pessimistically,” Pielke notes, “because it is only with a clear-eyed view of the mitigation challenge that we can ever hope to adopt effective policies. We hope that our analysis is one step toward such a clear-eyed view.“


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