2. The ecological impacts of climate change
Climate Change and Biodiversity Conservation
That humaninduced climatic
change does indeed pose a major threat to biodiversity has been
known for more than a decade. Several wideranging reviews
published during that time have tried to take stock of the range
of potential impacts across the globe. WWF is working to develop
a strong scientific basis for understanding the potential impacts
on wildlife and ecosystems. A first step is to identify those
biomes and ecosystems that may be most sensitive to climate change.
Most vulnerable will be those habitats where the first impacts
are likely to occur, where the most serious adverse effects may
arise, or where the least adaptive capacity exists. Table 1 gives
an overview of these "front line" ecosystems and some
of the climatic variables that influence them.
Table1. Most sensitive ecosystem
types and climatic variables most likely to influence them
Biome, ecosystem, or landscape type
| Key climate variables
|
Mangroves
| Relative rate of sea-level rise
Storm frequency and severity
|
Coral Reefs
| Relative rate of sea-level rise
Storm frequency and severity
Sea-surface temperature
|
Coastal marshes
| Relative rate of sea-level rise
Storm frequency and severity
|
Tropical Montane Forest
| Cloud cover and sunlight hours
Hurricane frequency and severity
Drought frequency and annual rainfall distribution
|
Raised peat bogs
| Mean summer temperature
Mean annual precipation
|
Alpine/Mountains
| Mean annual temperature
Snow fall and melt
Growing season length
|
Boreal forest
| Mean annual temperature
Fire frequency and severity
Storm frequency and severity
Growing season length
|
Arctic
| Mean annual temperature
Season length
Precipitation
Timing and extent of ice melt
|
Low-lying islands
| Relative sea-level rise
Storm frequency and severity
|
Arid and semi-arid areas
| Precipitation patterns
Minimum winter temperatures
|
For some ecosystems, such as coral reefs and tropical forests,
climate change is presently a lowlevel threat in comparison
with current environmental pressures and degradation. In coming
decades, as habitats decline and become more fragmented, and their
communities less diverse, there is every likelihood that the rate
of climate change will increase. As natural systems lose their
resilience, the threat of climatic impacts will become more acute,
and act as a cumulative stressor in addition to preexisting
problems. Much of today's discussion about climate change centres
on predicting what could happen to today's ecosystems over the
course of a few years or decades. However, an even longerterm
view is required if biological diversity is to be protected for
generations to come.
Most ecological impact studies have suffered from four central
problems:
- Lack of reliable regional climate change scenarios and information
about changes in weather variability and seasonality
- Lack of longterm ecological data sets
- Major gaps in current scientific understanding of community
and population ecology
- The difficulty of differentiating climate change impacts from
other stressrelated environmental degradation.
These barriers to knowledge are typical of those confronting scientists
in dealing with any complex set of problems. The difference in
the case of climate change is that policymakers urgently
require some indication of the probability of damage to ecosystems
in order to guide their actions in planning to reduce future levels
of pollution. At the "Earth Summit" of 1992 in Rio de
Janeiro more than 150 countries signed the UNFCCC and committed
themselves to meeting its objectives. The wording of the convention
specifically rules out lack of scientific certainty as a reason
for inaction. Indeed, conservation biologists have longknown
that uncertainty as to how ecosystems react to environmental pressures
dictates the adoption of the the most conservative and broadranging
protection strategies. It is simpler to plan conservation when
the threats are clearly defined and easily predictable. Climate
change impacts at the level of individual ecosystems are still
highly unpredictable, and therefore present the kind of danger
that requires increased conservation commitment. In the case of
climate change, the most effective strategy to protect biodiversity
will be a parallel approach which seeks both to reduce greenhouse
gas emissions, and to increase the resilience of natural ecosystems
through better management and protection.
Degraded natural ecosystems will be more
vulnerable to climate change
|
Scientists, therefore, must endeavour to provide
the best available information to policymakers and help
provide them also with some of the tools to analyse its policy
implications. One of the tools they require is a methodology for
assessing the meaning of the phrase used in Article 2 of the convention
which outlines the major objective of controlling greenhouse gas
emissions in order to allow "ecosystems to adapt naturally"
to change. This begs the question how much climate change is too
much?
The climate is likely to change so fast
that many species will be unable to adapt in time
|
Some scientists have suggested that a total
increase in global annual average temperature of 2°C,
or a rate of change of 0.1°C
a decade should be set as targets under the convention in order
to protect nature. But even these targets (which would be substantially
exceeded under current emissions projections) could not prevent
significant damage to many ecosystems. For most species, any change
in average climatic conditions will have some, often negative,
impact. If ecosystem protection is a genuine objective of the
Climate Convention, then climate change targets should aim to
cap warming at no more than 1°C
and at a rate of less than 0.01°C
a decade (see also `Temperate and boreal forests' on page 12).
Any greater change will undoubtedly have severe negative impacts
and cause irreversible alterations in our planet's natural habitats.
It is difficult to define natural adaptation. Instances of change
need to be related directly to human activity. Generalized trends
over geological time can be relatively easily identified in this
way. For example, the changes in distribution of various tree
species between glaciations can be linked to natural, longterm
variations in the Earth's climate. The creation of Britain's wildwood
by the spread, over thousands of years, of birch, then oak, alder,
and other tree species into moorland and tundra after the last
glaciation was natural adaptation to natural climate change. However,
the deforestation that destroyed approximately half of the climax
vegetation between 4000 BC and 500 BC was largely caused by human
development and agriculture. Species have evolved to cope with
natural climate changes in the absence of human interference.
It is doubtful that in a world under pressure from human development
and agriculture they will be so successful in adapting to rates
of climate change that will be at least an order of magnitude
faster than at any time in the last 10,000 years and possibly
the last 100,000 years.
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