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.
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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