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REPORTS - ASSESSMENT REPORTS |
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Synthesis Report - Question 7
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Climate Change 2001: Synthesis Report |
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Integrating
Near- and Long-Term Considerations
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Climate
change decision making is a sequential process under uncertainty. Decision
making at any point in time entails balancing the risks of either insufficient
or excessive action.
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Development
of a prudent risk management strategy involves careful consideration of
the consequences (both environmental and economic), their likelihood,
and society's attitude toward risk. The latter is likely to
vary from country to country and perhaps even from generation to generation.
This report therefore confirms the SAR finding that the value of better
information about climate change processes and impacts and society's
responses to them is likely to be great. Decisions about near-term climate
policies are in the process of being made while the concentration stabilization
target is still being debated. The literature suggests a step-by-step
resolution aimed at stabilizing greenhouse gas concentrations. This will
also involve balancing the risks of either insufficient or excessive action.
The relevant question is not "what is the best course for the next
100 years," but rather "what is the best course for the near
term given the expected long-term climate change and accompanying uncertainties."
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Stabilizing
atmospheric concentrations would depend upon emissions reductions beyond
those agreed to in the Kyoto Protocol. Most post-SRES scenario
analyses suggest that achievement of stabilization at 450 ppmv may require
emission reductions during the period 2008 to 2012 in Annex I countries
that are significantly stronger than the Kyoto Protocol commitments. This
analysis also suggests that achieving the aggregate Kyoto commitments
may be consistent with trajectories that achieve stabilization at 550
ppmv or higher. Other analyses suggest a more gradual departure from emissions
baselines even for 450 ppmv followed by sharper reductions in subsequent
budget periods. The path is influenced by the representation of inertia
in the system and expectations about how initial reductions by Annex I
countries may relate to the strength and scope of emissions limitation
in subsequent periods.
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Climate
change mitigation raises both inter-regional and inter-temporal equity
considerations.
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Differences in the distribution of technological,
natural, and financial resources among and within nations and regions,
and between generations, as well as differences in mitigation costs,
are often key considerations in the analysis of climate change mitigation
options. Much of the debate about the future differentiation
of contributions of countries to mitigation and related equity issues
also considers these circumstances.22
The challenge of addressing climate change raises an important issue
of equity, namely the extent to which the impacts of climate change
or mitigation policies ameliorate or exacerbate inequities both within
and across nations and regions, and between generations. Findings
with respect to these different aspects of equity include:
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Equity within nations: Most studies show that
the distributional effects of a carbon tax are regressive unless
the tax revenues are used either directly or indirectly in favor
of the low-income groups; the regressive aspect can be totally or
partially compensated by a revenue-recycling policy.
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Equity across nations and regions: Greenhouse
gas stabilization scenarios assessed in this report assume that
developed countries and countries with economies in transition limit
and reduce their greenhouse gas emissions first.23
Another aspect of equity across nations and regions is that
mitigation of climate change can offset inequities that would be
exacerbated by the impacts of climate change (see Question
6).
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Equity between generations: Stabilization of
concentrations depends more upon cumulative than annual emissions;
emissions reductions by any generation will reduce the need for
those by future generations.24
Inter-generational equity can be promoted by reducing climate
change impacts through mitigation of climate change by any generation,
since not only would impacts -- which are expected to affect especially
those with the fewest resources --
be reduced, but also subsequent generations will have less climate
change to adapt to (see Question
6).
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Figure 7-5: Carbon in
oil, gas, and coal reserves and resources is compared with historic fossil-fuel
carbon emissions over the period 1860–1998, and with cumulative carbon emissions
from a range of SRES scenarios and TAR stabilization scenarios until the
year 2100. Data for current reserves and resources are shown in
the lefthand columns. Unconventional oil and gas includes tar sands, shale
oil, other heavy oil, coal bed methane, deep geopressured gas, gas in aquifers,
etc. Gas hydrates (clathrates) that amount to an estimated 12,000 Gt C are
not shown. The scenario columns show both SRES reference scenarios as well
as scenarios that lead to stabilization of CO2 concentrations
at a range of levels. Note that if by the year 2100 cumulative emissions
associated with SRES scenarios are equal to or smaller than those for stabilization
scenarios, this does not imply that these scenarios equally lead to stabilization.
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