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| Question 9
What are the most robust findings
and key uncertainties regarding attribution of climate change and
regarding model projections of:
- Future emissions of greenhouse gases
and aerosols?
- Future concentrations of greenhouse gases
and aerosols?
- Future changes in regional and global
climate?
- Regional and global impacts of climate
change?
- Costs and benefits of mitigation and
adaptation options?
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Introduction
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The understanding of climate change, its impacts,
and the options to mitigate and adapt is developed through multi- and
interdisciplinary research and monitoring in an integrated assessment
framework. As understanding deepens, some findings become more
robust and some uncertainties emerge as critical for informed policy
formulation. Some uncertainties arise from a lack of data and a lack
of understanding of key processes and from disagreement about what is
known or even knowable. Other uncertainties are associated with predicting
social and personal behavior in response to information and events.
The uncertainties tend to escalate with the complexity of the problem,
as additional elements are introduced to include a more comprehensive
range of physical, technical, social, and political impacts and policy
responses. The climate responds to human influence without deliberation
or choice; but human society can respond to climate change deliberately,
making choices between different options. An objective of the TAR and
other IPCC reports is to explore, assess, quantify, and, if possible,
reduce these uncertainties.
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9.2
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In this report, a robust finding for climate change
is defined as one that holds under a variety of approaches, methods, models,
and assumptions and one that is expected to be relatively unaffected by
uncertainties. A robust finding can be expected to fall into the
categories of well-established (high level of agreement and high
amount of evidence) and established but incomplete (high level
of agreement, but incomplete evidence) in the literature. Robustness is
different from likelihood: A finding that an outcome is "exceptionally
unlikely" may be just as robust as the finding that it is "virtually
certain." A major development in the TAR is that of the multiple
alternative pathways for emissions and concentrations of greenhouse gases
as represented by the SRES. Robust findings are those that are maintained
under a wide range of these possible worlds.
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| 9.3 |
Key uncertainties in this context are those which,
if reduced, may lead to new and robust findings in relation to the questions
of this report. These findings may, in turn, lead to better or
more of the information that underpins policy making. The uncertainties
can never be fully resolved, but often they can be bounded by more evidence
and understanding, particularly in the search for consistent outcomes
or robust conclusions.
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9.4
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Robust findings and key uncertainties can be brought
together in the context of an integrated assessment framework.
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| 9.5 |
The integrated assessment framework described
in this report is used to bring together the robust findings and key uncertainties
in the model projections. Such a framework can encompass all the
disciplines involved in understanding the climate, the biosphere, and human
society. It emphasizes the linkages between the systems described in the
different Working Group reports of the TAR as well as considers linkages
between climate change and other environmental issues, and helps to identify
gaps in knowledge. It suggests how key uncertainties can affect the whole
picture. Figure 1-1 shows how
adaptation and mitigation can be integrated into the assessment. The human
and natural systems will have to adapt to climate change, and development
will be affected. The adaptation will be both autonomous and via government
initiatives, and adaptation actions will reduce (but cannot entirely avoid)
some of the impacts of climate change on these systems and on development.
Adaptation actions provide benefits but also entail costs. Mitigation is
unlike adaptation in that it reduces emissions at the start of the cycle,
it reduces concentrations (compared to what would otherwise occur), and
it reduces climate change and the risks and uncertainties associated with
climate change. It further reduces the need for adaptation, the impacts
of climate change, and effects on socio-economic development. It is also
different in that mitigation aims to address the impacts on the climate
system, whereas adaptation is primarily oriented to address localized impacts
of climate change. The primary benefit of mitigation is avoided climate
change, but it also has costs. In addition, mitigation gives rise to ancillary
benefits (e.g., reduced air pollution leading to improvements in human health).
A fully integrated approach to climate change assessment would consider
the whole cycle shown in Figure
1-1 dynamically with all the feedbacks but this could not be accomplished
in the TAR.
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| 9.6 |
Many of the robust findings as listed in Table
SPM-3 are concerned with the existence of a climate response
to human activities and the sign of the response. Many of the key
uncertainties are concerned with the quantification of
the magnitude and/or the timing of the response and the potential effects
of improving methods and relaxing assumptions. |
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