Potential, Barriers, Opportunities, Policies, and
Costs of Stabilizing Atmospheric Greenhouse Gas Concentrations in the
Long Term |
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7.21 | Cost of stabilization depends on both the target
and the emissions pathway. |
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7.22 | There
is no single path to a low-emission future, and countries and regions
will have to choose their own path. Most model results indicate that known
technological options20
could achieve a broad range of atmospheric CO2 stabilization
levels, such as 550 ppmv, 450 ppmv, or below over the next 100 years or
more, but implementation would require associated socio-economic and institutional
changes. To achieve stabilization at these levels, the scenarios
suggest that a very significant reduction in world carbon emissions per
unit of GDP from year 1990 levels will be necessary. For the crucial energy
sector, almost all greenhouse gas mitigation and concentration stabilization
scenarios are characterized by the introduction of efficient technologies
for both energy use and supply, and of low- or no-carbon energy. However,
no single technology option will provide all of the emissions reductions
needed for stabilization. Reduction options in non-energy sources and
non-CO2 greenhouse gases will also provide significant potential
for reducing emissions. |
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7.23 | The development
and diffusion of new economically competitive and environmentally sound
technology can substantially reduce the costs of stabilizing concentrations
at a given level. A substantial body of work has considered the
implication of technology development and diffusion on the cost of meeting
alternative stabilization levels. The principal conclusion is that the
cost of emissions mitigation depends crucially on the ability to develop
and deploy new technology. The value of successful technology diffusion
appears to be large and depends upon the magnitude and timing of emissions
mitigation, the assumed reference scenario, and the economic competitiveness
of the technology. |
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7.24 | The pathway
to stabilization can be as important as the stabilization level itself
in determining mitigation cost. Economic modeling studies completed
since the SAR indicate that a gradual near-term transition from the world's
present energy system towards a less carbon-emitting economy minimizes
costs associated with premature retirement of existing capital stock.
It also provides time for investment in technology development and diffusion,
and may reduce the risk of lock-in to early versions of rapidly developing
low-emission technology. On the other hand, more rapid near-term action
would increase flexibility in moving towards stabilization, decrease environmental
and human risks associated with rapid climatic changes, while minimizing
potential implications of inertia in climate and ecological systems (see
Question 5). It may also stimulate more rapid deployment
of existing low-emission technologies and provide strong near-term incentives
to future technological changes that may help reduce the risks of lock-in
to carbon-intensive technologies. It also would give greater scope for
later tightening of targets should that be deemed desirable in light of
evolving scientific understanding. |
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7.25 |
Cost-effectiveness studies with a
century time scale estimate that the mitigation costs of stabilizing CO2
concentrations in the atmosphere increase as the concentration stabilization
level declines. Different baselines can have a strong influence on absolute
costs. While there is a moderate increase in the costs when passing
from a 750 to a 550 ppmv concentration stabilization level, there is a
larger increase in costs passing from 550 to 450 ppmv (see Figure
7-3) unless the emissions in the baseline scenario are very low (see
Figure 7-4). Although model
projections indicate long-term global growth paths of GDP are not significantly
affected by mitigation actions towards stabilization, these do not show
the larger variations that occur over some shorter time periods, sectors,
or regions. These results, however, do not incorporate carbon sequestration,
and did not examine the possible effect of more ambitious targets on induced
technological change. Costs associated with each concentration level depend
on numerous factors including the rate of discount, distribution of emission
reductions over time, policies and measures employed, and particularly
the choice of the baseline scenario. For scenarios characterized by a
focus on local and regional sustainable development for example, total
costs of stabilizing at a particular level are significantly lower than
for other scenarios. Also, the issue of uncertainty takes on increasing
importance as the time frame is expanded. |
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7.26 | Energy R&D
and social learning can contribute to the flow and adoption of improved
energy technologies throughout the 21st century. |
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7.27 |
Lower emissions scenarios require
different patterns of energy resource development and an increase in energy
R&D to assist accelerating the development and deployment of advanced
environmentally sound energy technologies. Emissions of CO2
due to fossil-fuel burning are virtually certain to be the dominant influence
on the atmospheric CO2 concentration trend during the 21st
century. Resource data assessed in the TAR may imply a change in the energy
mix and the introduction of new sources of energy during the 21st century.
Fossil-fuel resources will not limit carbon emissions during the 21st
century (see Figure 7-5).
The carbon in proven conventional oil and gas reserves is much less than
the cumulative carbon emissions associated with stabilization of CO2
at levels of 450 ppmv or higher.21
These resource data may imply a change in the energy mix and the introduction
of new sources of energy during the 21st century. The choice of energy
mix and associated technologies and investments -- either more in the
direction of exploitation of unconventional oil and gas resources, or
in the direction of non-fossil energy sources or fossil energy technology
with carbon capture and storage -- will determine whether, and if so,
at what level and cost, greenhouse concentrations can be stabilized. |
WGIII TAR Sections 2.5.1-2, 3.8.4, & 8.4.5 |
Figure 7-3: The
mitigation costs (1990 US$, present value discounted at 5% per year for
the period 1990 to 2100) of stabilizing CO2 concentrations
at 450 to 750 ppmv are calculated using three global models, based on
different model-dependent baselines. Avoided impacts of climate change
are not included. In each instance, costs were calculated based on two
emission pathways for achieving the prescribed target: S (referred as
WGI emissions pathways in WGIII TAR) and WRE as described in response
to Question 6. The bars show cumulative carbon emissions
between the years 1990 and 2100. Cumulative future emissions until carbon
budget ceiling is reached are reported above the bars in Gt C. Important correction to figure 7.3 |
WGIII TAR Sections 2.5.2, 8.4.1, 8.4.3, & 10.4.6 |
Other reports in this collection |