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4.1. Has climate change already started to affect us?
4.1.1. Regional
changes in climate, particularly increases in temperature, have
already affected a diverse set of physical and biological systems
in many parts of the world.
Examples include: shrinkage of glaciers, thawing
of permafrost, later freezing and earlier break-up of ice on rivers
and lakes, lengthening of mid- to high-latitude growing seasons,
poleward and altitudinal shifts of plant and animal ranges, declines
of some plant and animal populations, and earlier flowering of trees,
emergence of insects and egg-laying in birds. More...
4.1.2. Regarding
human systems, there are preliminary indications that some social
and economic systems may have been affected by the recent increasing
frequency of floods and droughts in some areas. More...
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4.2. How potentially could climate change affect us?
4.2.1. Natural
systems can be especially vulnerable
to climate
change because of limited adaptive
capacity. While some species may benefit from climate change,
existing risks of extinction could increase for some more vulnerable
species. The risk of damage will increase with the magnitude and
rate of climate change. More...
4.2.2. Human
systems that are sensitive
to climate
change include mainly water resources; agriculture (especially
food security) and forestry; coastal zones and marine systems (fisheries);
human settlements, energy, and industry; insurance and other financial
services; and human health. Vulnerability
varies with geographic location, time, and social, economic, and
environmental conditions. Some effects will be adverse
but some others beneficial.
More...
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4.3. What other major impacts could climate change possibly have?
Some extreme events such as droughts, floods, heat
waves, avalanches, and windstorms are projected to increase in frequency
and/or severity, others such as cold spells are projected to decrease.
The damage, hardship, and death caused is also expected to increase
with global warming (see Figure
SPM-2). The impacts are expected to fall disproportionately
on the poorer regions. More...
There is a potential for large-scale and possibly
irreversible impacts but this risk has yet to be reliably quantified.
Examples include:
- slowing of the warm North Atlantic currents,
- large reductions in the Greenland and West Antarctic Ice Sheets
and
- accelerated global warming due to releases of terrestrial carbon
from permafrost regions and methane from hydrates in coastal sediments.
The likelihood of many of these changes is probably very low but
is expected to increase with the rate, magnitude, and duration of
climate
change. More...
See Table
SPM-1: Examples of impacts resulting from projected changes
in extreme climate events.
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4.4. What should be done?
Adaptation could reduce adverse impacts of climate
change and enhance beneficial impacts, but will incur costs
and will not prevent all damages. It is necessary to complement
mitigation
efforts with adaptation. More...
Based on a few published estimates, global warming
of up to a few degrees C would produce:
- net economic losses in many developing countries (low confidence6);
the higher the warming the greater the losses (medium confidence6).
- A mixture of economic gains and losses (low confidence6)
in developed countries, and losses for larger temperature increases
(medium confidence6).
- Decreases in world gross domestic product (GDP) of a few percent
(low confidence6),
and increasing net losses for larger increases in temperature
(medium confidence6)
(see Figure
SPM-2). More...
Policies that lessen pressures on resources, improve
management of environmental risks, and increase the welfare of the
poorest could simultaneously advance sustainable development and
equity, enhance adaptive
capacity, and reduce vulnerability to climate and other stresses.
More...
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