4.17 | Many natural and managed
ecosystems may change abruptly or non-linearly during the 21st century.
The greater the magnitude and rate of the change, the greater the risk of
adverse impacts. |
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4.18 | Changes in climate could
increase the risk of abrupt and non-linear changes in many ecosystems, which
would affect their biodiversity, productivity, and function. For
example, sustained increases in water temperatures of as little as 1°C,
alone or in combination with any of several stresses (e.g., excessive pollution
and siltation), can lead to corals ejecting their algae (coral bleaching;
see Figure 4-3 and Question
2), the eventual death of the corals, and a possible loss of biodiversity.
Climate change will also shift suitable habitats for many terrestrial and
marine organisms polewards or terrestrial ones to higher altitudes in mountainous
areas. Increased disturbances along with the shift in habitats and the more
restrictive conditions needed for establishment of species could lead to
abrupt and rapid breakdown of terrestrial and marine ecosystems, which could
result in new plant and animal assemblages that are less diverse, that include
more "weedy" species, and that increase risk of extinctions (see
Question 3). |
WGII TAR Sections 5.2, 6.4.5, & 17.2.4 | ||
4.19 | Ecological systems have many interacting non-linear processes and are thus subject to abrupt changes and threshold effects arising from relatively small changes in driving variables, such as climate. For example:
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WGII SAR Sections 13.2.2 & 13.6.2 |
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4.20 | Large-scale changes in vegetation
cover could affect regional climate. Changes in land surface characteristics,
such as those created by land cover, can modify energy, water, and gas fluxes
and affect atmospheric composition creating changes in local/regional climate
and thus changing the disturbance regime (e.g., in the Arctic). In areas
without surface water (typically semi-arid or arid), evapotranspiration
and albedo affect the local hydrologic cycle, thus a reduction in vegetative
cover could lead to reduced precipitation at the local/regional scale and
change the frequency and persistence of droughts. |
WGII TAR Sections 1.3.1, 5.2, 5.9, 10.2.6.3, 13.2.2, 13.6.2, & 14.2.1 | ||
WGII TAR Section 17.2.4 |
Other reports in this collection |