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REPORTS - ASSESSMENT REPORTS |
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Synthesis Report - Question 4
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Climate Change 2001: Synthesis Report |
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| Question 4
What is known about the influence of the
increasing atmospheric concentrations of
greenhouse gases and aerosols, and the projected human-induced change
in climate regionally and globally on:
- The frequency and magnitude of climate
fluctuations, including daily, seasonal, inter-annual, and decadal
variability, such as the El Niņo Southern Oscillation cycles and
others?
- The duration, location, frequency, and
intensity of extreme events such as heat waves, droughts, floods,
heavy precipitation, avalanches, storms, tornadoes, and tropical
cyclones?
- The risk of abrupt/non-linear changes
in, among others, the sources and sinks of greenhouse gases, ocean
circulation, and the extent of polar ice and permafrost? If so,
can the risk be quantified?
- The risk of abrupt or non-linear changes
in ecological systems?
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4.1
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This answer focuses on projected changes in the frequency
and magnitude of climate fluctuations as a result of increasing concentrations
of greenhouse gases and aerosols. Particular emphasis is placed on changes
in the frequency, magnitude, and duration of climatic extremes, which
represent important climate change risks for ecological systems and socio-economic
sectors. Projected abrupt or other non-linear changes in the biophysical
system are discussed here; the gradual changes in the physical, biological,
and social systems are discussed in Question 3.
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| 4.2 |
Models project that increasing atmospheric
concentrations of greenhouse gases will result in changes in daily, seasonal,
inter-annual, and decadal variability. There is projected to be a
decrease in diurnal temperature range in many areas, with nighttime lows
increasing more than daytime highs. A number of models show a general decrease
of daily variability of surface air temperature in winter and increased
daily variability in summer in the Northern Hemisphere land areas. Current
projections show little change or a small increase in amplitude for El Niño
events over the next 100 years. Many models show a more El Niño-like
mean response in the tropical Pacific, with the central and eastern equatorial
Pacific sea surface temperatures projected to warm more than the western
equatorial Pacific and with a corresponding mean eastward shift of precipitation.
Even with little or no change in El Niño strength, global warming
is
likely to lead to greater extremes of drying and heavy rainfall and increase
the risk of droughts and floods that occur with El Niño events in
many different regions. There is no clear agreement between models concerning
the changes in frequency or structure of other naturally occurring atmosphere-ocean
circulation pattern such as the North Atlantic Oscillation (NAO).
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WGI TAR Sections 9.3.5-6,
& WGII TAR Section 14.1.3 |
| 4.3 |
The duration, location, frequency, and intensity
of extreme weather and climate events are likely to very likely to change,
and would result in mostly adverse impacts on biophysical systems.
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| 4.4 |
Natural circulation patterns, such as ENSO and NAO, play
a fundamental role in global climate and its short-term (daily, intra- and
inter-annual) and longer term (decadal to multi-decadal) variability. Climate
change may manifest itself as a shift in means as well as a change in preference
of specific climate circulation patterns that could result in changes in
the variance and frequency of extremes of climatic variables (see Figure
4-1).
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WGI TAR Sections 1.2 &
2.7 |
| 4.5 |
More hot days and heat waves and fewer
cold and frost days are very likely over nearly all land areas. Increases
in mean temperature will lead to increases in hot weather and record hot
weather, with fewer frost days and cold waves (see Figure
4-1a,b). A number of models show a generally decreased daily variability
of surface air temperature in winter and increased daily variability in
summer in Northern Hemisphere land areas. The changes in temperature extremes
are likely to result in increased crop and livestock losses, higher energy
use for cooling and lower for heating, and increased human morbidity and
heat-stress-related mortality (see Table
4-1). Fewer frost days will result in decreased cold-related human morbidity
and mortality, and decreased risk of damage to a number of crops, though
the risk to other crops may increase. Benefits to agriculture from a small
temperature increase could result in small increases in the GDP of temperate
zone countries.
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WGI TAR Sections 9.3.6 &
10.3.2, & WGII
TAR Sections 5.3, 9.4.2,
& 19.5 |
| 4.6 |
The amplitude and frequency of extreme
precipitation events is very likely to increase over many areas and
the return period for extreme precipitation events are projected to decrease.
This would lead to more frequent floods and landslides with attendant loss
of life, health impacts (e.g., epidemics, infectious diseases, food poisoning),
property
damage, loss to infrastructure and settlements, soil erosion, pollution
loads, insurance and agriculture losses, amongst others. A general drying
of the mid-continental areas during summer is likely to lead to increases
in summer droughts and could increase the risk of wild fires. This general
drying is due to a combination of increased temperature and potential
evaporation that is not balanced by increases in precipitation. It is likely
that global warming will lead to an increase in the variability of Asian
summer monsoon precipitation.
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WGI TAR Section 9.3.6 &
WGII TAR Sections 4.3.8, 9.5.3,
9.7.10, & 9.8 |
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Figure 4-1: Schematic
diagrams showing the effects on extreme temperatures when (a) the
mean increases, leading to more record hot weather, (b) the variance increases,
and (c) when both the mean and variance increase, leading to much more record
hot weather. |
WGI TAR Figure 2.32 |
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