climate change on UAE - Stockholm Environment Institute-US Center

populate itself, and imbalances in the food-web,
meaning that there is either not enough food for
top predators or there are too few predators to
control the population of prey species. In these
circumstances, the imbalances can quickly
stack up synergistically in a positive feedback
cycle: for example, as top predators dwindle,
prey species multiply quickly and begin to
deplete food sources for other species or <strong>change</strong>
the physical or chemical properties of their
ecosystem. For example, overfishing of Codfish
in the rich kelp (seaweed) forests of the Gulf of
Maine allowed sea urchins to prosper, which in
turn destroyed the kelp habitat (Jackson et al,
2001). Cod is now extinct in the North Atlantic,
and the habitat has, for all intensive purposes,
<strong>change</strong>d permanently.
Habitat destruction results in the loss of
ecosystem area or an impedance in ecosystem
function, and is, by far, the most pressing threat
to biodiversity worldwide. Pollution and habitat
misuse can destroy or impede key elements of
an ecosystem, lending to severe imbalances and
loss of ecosystem functionality. For example,
overgrazing in arid ecosystems commonly leads
to the trampling of biogenic crusts and the loss
of critical vegetation cover, which, in turn, leads
to increased runoff and erosion, nutrient losses,
and can promote invasive species.
The direct loss of habitat by land use <strong>change</strong> can
also result in the loss of biodiversity as parts of
an ecosystem are transformed for another use,
there is less area for the native ecosystem to
use. The relationship between species diversity
and area has been recognized since at least
the early 20 th century, and was formalized by
Williams (1964) and, later, Rosenzsweig (1995)
as a logarithmic curve. In numerous studies, as
larger areas are examined, the number of species
increases (i.e. from a small plot to a continent).
Geographical constraints, the ability to move,
migrate, and compete, and the ability to
escape small-scale disturbances all govern the
relationship between area and speciation.
Within a specific type of biome or ecosystem, as
the physical size of the ecosystem is reduced,
the number of species which can be supported
in the ecosystem is also reduced. Expansion
of urban areas, deforestation, sedimentation,
and agricultural expansion are all mechanisms
of direct habitat destruction. Fragmentation
restricts the ability for species to migrate or
expand. Thus, even if total habitat space is
large, but is subdivided into small fragments,
the net effect results in small, non-diverse (and
often functionally deficient) ecosystems.
Finally, <strong>climate</strong> <strong>change</strong> may already be
responsible for some species losses and
threatens to lead to rampant reductions in
biodiversity globally. Climate <strong>change</strong> shifts the
basic substrates upon which ecosystems rely:
as temperatures increase and precipitation
patterns are altered, ecosystems which used to
thrive in one region may be displaced to other
areas or disappear altogether. For many biomes
around the world, this shift may look like a mass
movement of ecosystems towards the poles or
higher elevations, while ecosystems already
near the poles or at high elevation may be lost
completely.
While the story is both complicated and
uncertain, it is likely that many sedentary
or non-migrating species will be unable to
move at the pace of <strong>climate</strong> <strong>change</strong>, and even
migratory species may find their migratory
routes falling out of synchrony with weather
and food patterns. For all of these reasons, it
is likely that <strong>climate</strong> <strong>change</strong> alone will lead to
significant biodiversity losses (Sala et al., 2000),
and the effect will be compounded where there
are already significant environmental stresses,
such as those described previously (Thomas et
al, 2004).
8.1. Biodiversity and ecological
thresholds
In 2000, Sala and others predicted that
“Mediterranean <strong>climate</strong> and grassland
ecosystems likely will experience the greatest
proportional <strong>change</strong> [loss] in biodiversity”
by 2100 due to the combined influence of
<strong>climate</strong> <strong>change</strong>, land use <strong>change</strong>, <strong>change</strong>s in
atmospheric CO 2
, and introduced (invasive)
species. Except for far northern and southern
latitudes, where <strong>climate</strong> <strong>change</strong> is expected to
have the most significant impacts, <strong>change</strong>s in
land use are expected to be responsible for the
heaviest toll on biodiversity. According to the
Sala et al. (2000) analysis, if we assume that
interactions amongst the drivers of biodiversity
<strong>change</strong> are synergistic and multiplicative,
164
Climate Change Impacts, Vulnerability & Adaptation