3. Worldwide loss of biodiversity
Climate Change and Biodiversity Conservation
Of some things there is no doubt.
The Earth's biodiversity is undergoing a highly deleterious simplification
as the result of human activities. Biological diversity is generally
taken to mean the combination of genetic variation, species richness,
and ecosystem and landscape diversity. Biodiversity at all levels
is currently being lost at an unprecedented rate. Just one measure
of this loss is the rate of species extinctions. Background extinction
rates through geological time have been roughly estimated at the
rate of one mammal and two birds every 400 years. Documented extinctions
for mammals and birds during the last 400 years are already at
50 times that rate and even this figure is undoubtedly a major
underestimate. The highest levels of biodiversity are in the tropics,
particularly in tropical forests. Estimates for the total number
of species range between five and 30 million species, less than
two million of which have been described by science. The top end
of this range is based largely on estimates of insect species
richness in tropical forests. Current rates of extinction from
the tropical forest biome alone have been estimated at 1-11 per
cent per decade.
There is a tendency for the issue of species extinctions to gain
the greatest attention in any public debate about conservation
and biodiversity loss. In fact, ecologists are becoming increasingly
concerned with maintaining diversity at all levels. Today's conservationists
are concerned with preserving and maintaining the full range of
biodiversity and functional values of ecosystems, not merely popular
species or more unusual habitats. The concept of ecosystem integrity
is often used to describe the full set of values that we should
strive to maintain in our natural areas. American conservation
biologist Reed Noss has argued that preserving ecosystem integrity
involves elements of ecosystem health, biodiversity, stability,
sustainability, naturalness, and beauty. In other words, we should
seek to conserve a broad range of interlinked values in ecosystems,
the subsequent outcome of which is likely to determine the robustness,
or otherwise, of natural areas to a changing climate.
Environmental hazards: habitat destruction,
pollution, over exploitation of natural resources, climate
change
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Humaninduced climate change adds another
layer to the already complex interplay of forces, natural and
anthropogenic, that shape our natural world. For too long nature
has been regarded as stable or constant in its makeup. It
is, in fact, highly dynamic, with most ecosystems being in some
form of transient state. It has been said with good reason that
"ecosystems are not only more complex than we think, but
more complex than we can think".
The need to prepare for adaptation to climate change is highlighting
the issue of ecological dynamism and complexity for the scientific
community and the public at large. Climate change impacts will
not be imposed on stable communities of plants and animals, but
on ecosystems that are constantly in a state of flux. For this
reason, impacts will be particularly hard to predict.
Further complicating the analysis of climate change impacts are
the effects of ongoing environmental degradation. Leading causes
of biodiversity loss worldwide include habitat destruction, pollution,
introduction of alien species, and overexploitation of wildlife,
fisheries, and forests. High amongst the driving forces behind
these problems are demographic change (including population growth),
consumption patterns, inefficient energy use, and commodity trade.
The net result of these many stresses is a loss of diversity and
a simplification of ecological complexity. These changes reduce
the resilience of ecosystems and weaken their capacity to adapt
to climate change. Ecological complexity is a prerequisite for
ameliorating the negative impacts of global climate change.
Already there are indications of how climate change could be affecting
ecosystems and species worldwide. These include:
- A warming trend and decreasing spring rainfall during the
last 100 years have increased the risk of wildfires in Yellowstone
National Park.
- The warmer, drier climate this century has also allowed an unprecedented
expansion of juniper woodlands in the intermountain region of
the western US. And subalpine firs and mountain hemlock
are invading alpine flower meadows.
- Climate change is one of the key factors that threatens a rare
fritillary butterfly with extinction as the last remaining mountaintop
habitats of Colorado become too warm.
- Sediment cores from the frozen mud of higharctic lakes
on Canada's remote Ellesmere Island reveal that after nearly 8,000
years of stability in lake vegetation, the 19th and 20th centuries
brought about major changes in lake flora, consistent with a warming
trend.
An increase in the death of coral reefs as a result of "bleaching"
associated with warmer water temperatures has been reported recently
from reefs around the world, including those in Indonesia, the
Philippines, Jamaica, and Pacific island nations such as the Cook
Islands and American Samoa.
- Deforestation in the rainforests of Xishuangbanna in South China
has led to local climate changes, including a reduction in the
cloud and fog necessary to maintain moisturedependent plants
such as mosses, ferns, and orchids in the forest canopy.
- A longterm drying trend in central Panama appears to be
leading to major changes in forest composition and reduction in
diversity. In the rich tropical forests of Barro Colorado Island,
several shrub and tree species are heading for local extinction.
- The current severe die back of coastal mangrove forest on the
island of Bermuda has been strongly linked to sealevel rise.
Additional signposts to the future climate can be discerned from
examining the pattern of extreme weather events. The impacts of
disasters such as Hurricane Hugo's devastating run through the
Caribbean in 1988, the southern African drought of 1991-1992 or
1995's catastrophic floods in northern Europe are likely to be
repeated more frequently as the climate warms.
Recent extreme weather events are a foretaste
of the future
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Of special concern is the phenomenon known
as El Niño, a periodic alteration of the winds and ocean
currents in the tropical Pacific. Weakening of the normal easterly
winds triggers El Niños by suppressing nutrientrich
coldwater upwellings and warming of the sea surface. The
severity of El Niños varies sharply, and whilst the weaker
ones are noticed mainly in South America, where marine fisheries
drop off markedly, stronger ones are felt around the world. There
have been nine El Niños in the last 40 years, but the strongest
of the century occurred in 1982-1983.
The global economic costs of damage from floods, droughts, and
hurricanes caused by this massive weather perturbation have been
estimated at well over US$8 billion. During the 1982-1983 El Niño,
tropical storms hit islands that seldom suffer from such events,
including Hawaii and Tahiti. Huge forest fires raged in Indonesia
and Australia, and winter flooding spread throughout the southern
United States. Meanwhile the anchovy fishery off Peru and Ecuador
crashed, and episodes of bleaching due to the warm waters killed
off corals around the world. Huge portions of Pacific populations
of seabirds such as cormorants, terns, and boobies starved to
death, as did fur seals and sealions. Now, as the climate
warms, many scientists believe that El Niños may become
more frequent and severe, with their impacts becoming increasingly
devastating. Climate change may be taking us into unknown territory
and creating a world of violent and unpredictable weather.
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