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Biodiversity, Agriculture and Forestry, and Climate
Change
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| 8.13 |
Changes in terrestrial and marine ecosystems are
closely linked to changes in climate and vice versa. Changes in
climate and in atmospheric concentrations of CO2 cause changes
in the biodiversity and function of some ecosystems. In turn, ecosystem
changes influence the land-atmosphere exchange of greenhouse gases (e.g.,
CO2, CH4, and N2O) and of water and energy,
and change surface albedo. Therefore, understanding these combined effects
and feedbacks are a requisite for evaluating the future state of the atmosphere
and the natural systems and their biodiversity.
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 WGI
TAR Section 4.5.3 |
| 8.14 |
Natural climate variations have illustrated
the impacts of climate change on natural and managed ecosystems. The
impacts of floods, droughts, and heat waves are etched into human history.
Further, the warming events associated with El Niño illustrate that
changes in climate patterns adversely affect fish, marine mammals, and coastal
and ocean biodiversity. Coastal ecosystems -- such as coral reefs, salt
marshes, and mangrove forests -- are affected by sea-level rise, warming
ocean temperatures, increased CO2 concentrations, and changes
in storm frequency and intensity. Table 8-1
gives main implications of climate change for natural ecosystems at the
regional scale.
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WGII TAR Chapters 5 &
6 |
| 8.15 |
Climate change is but one of many stresses
on managed and unmanaged ecosystems. Land-use change, resource demands,
deposition of nutrients and pollutants, harvesting, grazing, habitat fragmentation
and loss, and invasive species are major stressors on ecosystems. They can
lead to species extinction, resulting in losses of biodiversity. Therefore,
climate change constitutes an additional stress and could change or endanger
ecosystems and the many services they provide. As a result, the impact of
climate change will be influenced by management of natural resources, adaptation,
and interaction with other pressures. Figure
8-2 exemplifies the manner in which climate change interacts with other
factors in food supply and demand.
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WGII TAR Chapters 5 &
6, & WGIII
TAR Sections 4.1-2 |
| 8.16 |
Climate change can influence the distribution
and migration of species in unmanaged ecosystems. Populations of
many species are already threatened with extinction and are expected to
be placed at greater risk by the stresses of changing climate, rendering
portions of their current habitat unsuitable. Vegetation distribution models
since the SAR suggest that a mass ecosystem or biome movement is most unlikely
to occur because differerent species have different climate tolerance and
different migration abilities, and are affected differently by the arrival
of new species. Lastly, in a related sense, climate change can enhance
the
spreading of pests and diseases, thereby affecting both natural
ecosystems, crops, and livestock (e.g., changes in temperature and humidity
thresholds allow pests and diseases to move to new areas).
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WGII TAR Chapter 5 |
| 8.17 |
Carbon storage capacities of managed and
unmanaged ecosystems, particularly forests, influence impacts and feedbacks
with climate change. For example, forests, agricultural lands, and
other terrestrial ecosystems offer a significant carbon mitigation potential.
Although not necessarily permanent, conservation and sequestration may allow
time for other options to be further developed and implemented. Terrestrial
ecosystem degradation may be exacerbated by climate change, affecting the
storage of carbon, and adding to the stresses resulting from the current
deforestation practices. It should be noted that, if appropriate management
practices are not carried out, CO2 emissions in the future could
be higher. For example, abandoning fire management in forests or reverting
from direct seeding to intensive tillage in agriculture may result in rapid
loss of part, at least, of the accumulated carbon. |
WGIII TAR Section 4.3 &
SRLULUCF
SPM |
