| 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. Key uncertainties in this context are
those that, if reduced, may lead to new and robust findings in relation
to the questions of this report. In the examples in Table
SPM-3, many of the robust findings relate to 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 timing of the response. After addressing the attribution
of climate change, the table deals in order with the issues illustrated
in Figure SPM-1. Figure
SPM-10 illustrates some of the main robust findings regarding climate
change. Table SPM-3 provides
examples and is not an exhaustive list.
Significant progress has been made in the TAR in many aspects of the knowledge
required to understand climate change and the human response to it. However,
there remain important areas where further work is required, in particular:
- The detection and attribution of climate change
- The understanding and prediction of regional changes in climate and
climate extremes
- The quantification of climate change impacts at the global, regional,
and local levels
- The analysis of adaptation and mitigation activities
- The integration of all aspects of the climate change issue into strategies
for sustainable development
- Comprehensive and integrated investigations to support the judgment
as to what constitutes
"dangerous anthropogenic interference with the climate system."
| Table
SPM-3: Robust findings and key uncertainties.a |
| Robust Findings |
|
Key Uncertainties |
| Observations show Earth's surface
is warming. Globally, 1990s very likely warmest decade in instrumental
record (Figure SPM-10b).
[Q9.8]
Atmospheric concentrations of main anthropogenic greenhouse gases
(CO2 (Figure
SPM-10a), CH4, N2O, and tropospheric O3)
increased substantially since the year 1750. [Q9.10]
Some greenhouse gases have long lifetimes (e.g., CO2,
N2O, and PFCs). [Q9.10]
Most of observed warming over last 50 years likely due to increases
in greenhouse gas concentrations due to human activities. [Q9.8] |
Climate change and attribution |
Magnitude and character of natural
climate variability. [Q9.8]
Climate forcings due to natural factors and anthropogenic aerosols
(particularly indirect effects). [Q9.8]
Relating regional trends to anthropogenic climate change. [Q9.8
& Q9.22] |
| CO2concentrations increasing
over 21st century virtually certain to be mainly due to fossil-fuel
emissions (Figure SPM-10a).
[Q9.11]
Stabilization of atmospheric CO2 concentrations at 450,
650, or 1,000 ppm would require global anthropogenic CO2
emissions to drop below year 1990 levels, within a few decades,
about a century, or about 2 centuries, respectively, and continue
to decrease steadily thereafter to a small fraction of current emissions.
Emissions would peak in about 1 to 2 decades (450 ppm) and roughly
a century (1,000 ppm) from the present. [Q9.30]
For most SRES scenarios, SO2 emissions (precursor for
sulfate aerosols) are lower in the year 2100 compared with year
2000. [Q9.10] |
Future emissions and concentrations
of greenhouse gases and aerosols based on models and projections with
the SRES and stabilization scenarios |
Assumptions underlying the wide rangeb
of SRES emissions scenarios relating to economic growth, technological
progress, population growth, and governance structures (lead to
largest uncertainties in projections). Inadequate emission scenarios
for ozone and aerosol precursors. [Q9.10]
Factors in modeling of carbon cycle including effects of climate
feedbacks.b [Q9.10] |
| Global average surface temperature
during 21st century rising at rates very likely without precedent
during last 10,000 years (Figure
SPM-10b). [Q9.13]
Nearly all land areas very likely to warm more than the global
average, with more hot days and heat waves and fewer cold days and
cold waves. [Q9.13]
Rise in sea level during 21st century that will continue for further
centuries. [Q9.15]
Hydrological cycle more intense. Increase in globally averaged
precipitation and more intense precipitation events very likely
over many areas. [Q9.14]
Increased summer drying and associated risk of drought likely over
most mid-latitude continental interiors. [Q9.14] |
Future changes in global and regional
climate based on model projections with SRES scenarios |
Assumptions associated with a wide
rangec of SRES scenarios, as above. [Q9.10]
Factors associated with model projectionsc, in particular
climate sensitivity, climate forcing, and feedback processes especially
those involving water vapor, clouds, and aerosols (including aerosol
indirect effects). [Q9.16]
Understanding the probability distribution associated with temperature
and sea-level projections. [Q9.16]
The mechanisms, quantification, time scales, and likelihoods associated
with large-scale abrupt/non-linear changes (e.g., ocean thermohaline
circulation). [Q9.16]
Capabilities of models on regional scales especially regarding
precipitation) leading to inconsistencies in model projections and
difficulties in quantification on local and regional scales. [Q9.16] |
| Projected climate change will have
beneficial and adverse effects on both environmental and socio-economic
systems, but the larger the changes and the rate of change in climate,
the more the adverse effects predominate. [Q9.17]
The adverse impacts of climate change are expected to fall disproportionately
upon developing countries and the poor persons within countries.
[Q9.20]
Ecosystems and species are vulnerable to climate change and other
stresses (as illustrated by observed impacts of recent regional
temperature changes) and some will be irreversibly damaged or lost.
[Q9.19]
In some mid- to high latitudes, plant productivity (trees and some
agricultural crops) would increase with small increases in temperature.
Plant productivity would decrease in most regions of the world for
warming beyond a few °C. [Q9.18]
Many physical systems are vulnerable to climate change (e.g., the
impact of coastal storm surges will be exacerbated by sea-level
rise, and glaciers and permafrost will continue to retreat). [Q9.18] |
Regional and global impacts of changes
in mean climate and extremes |
Reliability of local or regional detail
in projections of climate change, especially climate extremes. [Q9.22]
Assessing and predicting response of ecological, social (e.g.,
impact of vector- and water-borne diseases), and economic systems
to the combined effect of climate change and other stresses such
as land-use change, local pollution, etc. [Q9.22]
Identification, quantification, and valuation of damages associated
with climate change. [Q9.16,
Q9.22 & Q9.26] |
| Greenhouse gas emission reduction
(mitigation) actions would lessen the pressures on natural and human
systems from climate change. [Q9.28]
Mitigation has costs that vary between regions and sectors. Substantial
technological and other opportunities exist for lowering these costs.
Efficient emissions trading also reduces costs for those participating
in the trading. [Q9.31
& Q9.35-36]
Emissions constraints on Annex I countries have well-established,
albeit varied, "spill-over" effects on non-Annex I countries.
[Q9.32]
National mitigation responses to climate change can be more effective
if deployed as a portfolio of policies to limit or reduce net greenhouse
gas emissions. [Q9.35]
Adaptation has the potential to reduce adverse effects of climate
change and can often produce immediate ancillary benefits, but will
not prevent all damages. [Q9.24]
Adaptation can complement mitigation in a cost-effective strategy
to reduce climate change risks; together they can contribute to
sustainable development objectives. [Q9.40]
Inertia in the interacting climate, ecological, and socio-economic
systems is a major reason why anticipatory adaptation and mitigation
actions are beneficial. [Q9.39] |
Costs and benefits of mitigation and
adaptation options |
Understanding the interactions between
climate change and other environmental issues and the related socio-economic
implications. [Q9.40]
The future price of energy, and the cost and availability of low-emissions
technology. [Q9.33-34]
Identification of means to remove barriers that impede adoption
of low-emission technologies, and estimation of the costs of overcoming
such barriers. [Q9.35]
Quantification of costs of unplanned and unexpected mitigation
actions with sudden short-term effects. [Q9.38]
Quantification of mitigation cost estimates generated by different
approaches (e.g., bottom-up vs. top-down), including ancillary benefits,
technological change, and effects on sectors and regions. [Q9.35]
Quantification of adaptation costs. [Q9.25] |
a. 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. Key
uncertainties in this context are those that, if reduced,
may lead to new and robust findings in relation to the questions of
this report. This table provides examples and is not an exhaustive
list.
b. Accounting for these above uncertainties leads to a range
of CO2concentrations in the year 2100 between about 490
and 1,260 ppm.
c. Accounting for these above uncertainties leads to a range
for globally averaged surface temperature increase, 1990-2100, of
1.4 to 5.8°C (Figure
SPM-10b) and of globally averaged sea-level rise of 0.09 to 0.88
m. |
|
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