Integrating
Near- and Long-Term Considerations
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.
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."
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.
Climate
change mitigation raises both inter-regional and inter-temporal equity
considerations.
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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