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REPORTS - ASSESSMENT REPORTS |
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Synthesis Report - Question 9
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Climate Change 2001: Synthesis Report |
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Future Changes in Regional and Global Climate
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| 9.12 |
The climate has changed during the 20th century; larger
changes are projected for the 21st century.
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9.13
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Under all SRES scenarios, projections show the global
average surface temperature continuing to rise during the 21st century
at rates of rise that are very likely to be without precedent during the
last 10,000 years, based on paleoclimate data (Figure
9-1b). It is very likely that nearly all land areas will warm
more rapidly than the global average, particularly those at high northern
latitudes in the cold season. There are very likely to be more hot days;
fewer cold days, cold waves, and frost days; and a reduced diurnal temperature
range.
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Q3.7, Q3.11,
& Q4.5 |
| 9.14 |
In a warmer world the hydrological cycle
will become more intense. Global average precipitation is projected
to increase. More intense precipitation events (hence flooding) are very
likely over many areas. Increased summer drying and associated risk of drought
is likely over most mid-latitude continental interiors. Even with little
or no change in El Niño amplitude, an increase in temperatures globally
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.
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Q2.24, Q3.8,
Q3.12, Q4.2,
& Q4.6 |
| 9.15 |
In a warmer world the sea level will rise,
primarily due to thermal expansion and loss of mass from glaciers and ice
caps, the rise being continued for hundreds of years even after stabilization
of greenhouse gas concentrations.
This is due to the long time scales on which the deep ocean adjusts to climate
change. Ice sheets will continue to react to climate change for thousands
of years. Models project that a local warming (annually averaged) of larger
than 3ºC, sustained for many millennia, would lead to virtually a complete
melting of the Greenland ice sheet with a resulting sea-level rise of about
7 m.
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Q3.9, Q3.14,
Q4.15, & Q5.4 |
| 9.16 |
Key uncertainties that influence the quantification
and the detail of future projections of climate change are those associated
with the SRES scenarios, and also those associated with the modeling of
climate change, in particular those that concern the understanding of key
feedback processes in the climate system, especially those involving clouds,
water vapor, and aerosols (including their indirect forcing). Allowing for
these uncertainties leads to a range of projections of surface temperature
increase for the period 1990 to 2100 of 1.4 to 5.8ºC (see Figure
9-1b) and of sea-level rise from 0.09 to 0.88 m. Another uncertainty
concerns the understanding of the probability distribution associated with
temperature and sea-level projections for the range of SRES scenarios. Key
uncertainties also affect the detail of regional climate change
and its impacts because of the limited capabilities of the regional models,
and the global models driving them, and inconsistencies in results between
different models especially in some areas and in precipitation. A further
key uncertainty concerns the mechanisms, quantification, time scales, and
likelihoods associated with large-scale abrupt/non-linear changes (e.g.,
ocean thermohaline circulation). |
Q3.6, Q3.9,
& Q4.9-19 |
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