4. Ecological limits to climate change
Climate Change and Biodiversity Conservation
Climate change will add to the stresses
causing environmental degradation, but the actual impacts of this
additional stress factor are hard to predict. It is therefore
necessary to try and make some generalizations about the potential
ecological limits to climate change in order to set emissions
reductions targets under the UNFCCC. Ecological limits can be
set using a combination of both scientific data and subjective
policy criteria. Within the context of the convention, the policy
criteria of most relevance to individual Parties will vary from
country to country. Whichever methodologies or forms of ecological
risk assessment techniques are used in this process, political
and value judgements will still need to be made.
There have been very few attempts to suggest critical levels of
climate change for ecosystems. This is partly due to the inappropriateness
of using global averages for ecosystem vulnerability analysis.
For example, while the Intergovernmental Panel on Climate Change
(IPCC) predictions of global sealevel rise are 4 cm per
decade over the next century, actual relative sealevel rise
for any particular coastal site is determined by a combination
of local sealevel rise, land subsidence, and sediment accretion
rates, and is further influenced by human coastal management and
transient events such as storms. Actual, relative sealevel
rise rates for 18 sites on the east coast of the USA have been
estimated to range from 0.9 mm per year to 13.0 mm per year.
It makes sense to predict and analyse climate
change impacts at local and regional levels
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The question of whether biomes or ecosystems
are threatened by climate change also needs to be looked at in
the context of spatial scale. The coral reef biome may not be
in great danger from climate change on a global scale (it may
even expand into new areas), but at a local level numerous individual
reefs or reef species may be threatened with extinction, with
serious consequences for the local fishing communities which depend
on coral reefs for their livelihood. Sensitivity of individual
reefs is increased by multiple and varying types of anthropogenic
stresses.
Scientifically supportable assessments require a regionally based
approach if they are to be of use to policymakers. Whilst
biodiversity conservation is a global goal, and its achievement
is to the benefit of humankind, its practice is generally focused
on national and sitespecific actions. It makes sense, therefore,
to try to identify critical climate change criteria and potential
indicator systems and species for different regions. In the Netherlands,
for instance, it has been suggested that changes in distribution
of climatesensitive species such as the longeared
owl, swallowtail butterfly, or prickly lettuce will make good
indicators. In addition to monitoring of biological indicators,
the predictive capacity of regional climate changes will need
to be radically improved in order to quantify threats to biodiversity
and conservation at a local scale.
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