IPCC’s CO2 Emissions-Reduction Assumptions Overly Optimistic?

National Center for Atmospheric Research
Public release date: 2-Apr-2008

Contact: Rachael Drummond

Tom Wigley

National Center for Atmospheric Research/University Corporation for
Atmospheric Research

Roger Pielke Jr.
University of Colorado, Boulder

Emission reduction assumptions for carbon dioxide overly optimistic, study says

BOULDER–Reducing global emissions of carbon dioxide (CO2) over the
coming century will be more challenging than society has been led to
believe, according to a new research commentary appearing April 3 in

The authors, from the University of Colorado at Boulder, the National
Center for Atmospheric Research (NCAR) in Boulder, and McGill
University in Montreal, say the Intergovernmental Panel on Climate
Change (IPCC) has significantly underestimated the technological
challenges of reducing CO2 emissions. The study, “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.

“In the end, there is no question whether technological innovation is
necessary–it is,” write the authors in the Nature commentary. “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.”

Recent changes in “carbon intensity”–CO2 emissions per unit of
energy consumed–already are higher than those predicted by the IPCC
because of rapid economic development, says lead author Roger Pielke
Jr. of the University of Colorado. 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 for CO2 concentration
stabilization, 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. This division hides the
full challenge associated with stabilizing the amount of carbon
dioxide in the atmosphere. The Nature commentary points out, for
example, 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 percent of the total carbon removed from the
energy supply over the coming century would occur spontaneously.

“According to the IPCC report, the majority of the emission
reductions required to stabilize CO2 concentrations are assumed to
occur automatically,” says Pielke. “Not only is this reduction
unlikely to happen under current policies, but we are moving in the
opposite direction right now. We believe these kinds of assumptions
in the analysis blind us to reality and could potentially distort our
ability to develop effective policies.”

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, notes co-author Tom Wigley of

“Stabilization is a more daunting challenge than many realize and
requires a radical ‘decarbonization’ of energy systems,” Wigley says.
“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 CO2.”

Unlike the IPCC assumptions of large 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,” says
co-author Christopher Green of McGill University.

“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.”


The University Corporation for Atmospheric Research operates the
National Center for Atmospheric Research under primary sponsorship by
the National Science Foundation. Opinions, findings, conclusions, or
recommendations expressed in this release do not necessarily reflect
the views of the National Science Foundation.


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