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| Sea ice in the Beaufort Sea, with the Arctic National Wildlife Refuge, Alaska, in the background. © US Fish and Wildlife Service |
Climate change will increasing drive biodiversity loss, affecting both individual species and their ecosystems. An ecosystem can be defined as a community of plant and animal species and the physical environment that they occupy, which includes the climate regime. When climate conditions change, unexpected results may follow. Each species will respond in an individual fashion, according to its climate tolerances and its ability to disperse into a new location, alter its phenology (e.g. breeding date) or adapt to shifting food sources. It is difficult to predict the overall result of changes in the abundance of herbivores and food plants, predators and prey.
Many studies have attempted to project the rate and extent of terrestrial ecosystem response to climate change, some using simple models assuming that entire ecosystems will shift to follow the changing climate, and others using ‘plant functional type’ models featuring the responses of different types of herbs, bushes and trees. Vegetation zones are typically expected to move towards higher latitudes or higher altitudes following shifts in average temperatures.
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| Innoko National Wildlife Refuge, Alaska. © US Fish and Wildlife Service |
The vulnerability of an ecosystem to climate change depends on its species’ tolerance of change, the degree of change, and the other stresses already affecting it. For example, coral reefs already polluted by sediment and nutrient run-off may find it more difficult to survive increasing ocean temperatures. Climate change can also increase an ecosystem’s vulnerability to existing pressures. For example, where fire is used to clear agricultural land, drier, warmer conditions will make an adjacent forest more susceptible to burning. In addition, disturbances such as fires, floods and insect plagues are expected to become more frequent as a result of climate change.
Up to a point, the increased concentrations of atmospheric carbon dioxide that are driving global warming also have a direct effect on plants, both increasing rates of photosynthesis and improving water use efficiency. This increases tolerance to drought, so may help some terrestrial ecosystems to withstand the effects of climate change.
Marine ecosystems will be affected not only by an increase in sea temperature and changes in ocean circulation, but also by ocean acidification, as the concentration of dissolved carbon dioxide (carbonic acid) rises. This is expected to negatively affect shell forming organisms, corals and their dependent ecosystems, with some researchers warning of catastrophic results.
Polar ecosystems are especially vulnerable to climate change, with effects such as thawing permafrost, decreased snow cover, losses from ice sheets and changes in ocean temperatures. Impacts on Arctic biodiversity are already being observed.
Resources
Sensitive ecosystems analysis (2000)
A review of the vulnerability of terrestrial and marine ecosystems to climate change was undertaken in 1999-2000. The following table illustrates the potential impacts of changes in specific climate-related variables for each ecosystem.
|
Biome, ecosystem. Landscape type
|
Key
climatic variables
|
Implications
for biodiversity
|
|
Wetlands
|
- Mean
summer temperature
- Mean
annual precipitation
- Flooding
|
- Increased
variability in the hydrological cycle leaving inland wetlands
to dry out with lower species diversity
- Warming
of 3 - 4°C. could eliminate 85% of all remaining wetlands
|
|
Coastal marshes
|
- Relative
rate of sea-level rise, changes in hydrological balance
- Storm
frequency and severity
|
- Habitat
loss of estuaries and deltas, particularly where these are backed
by agricultural or urban land, preventing natural retreat
- Implications
on migratory species and their flyway patterns
|
|
Forests
(general)
|
- Changes
in rainfall, temperature and potential evapotranspiration.
- Increased
frequency of fire and storms.
|
- Major
changes in vegetation types, forests may disappear in certain
areas at a rate faster then the potential rate of mirgration to,
or re-growth in, new areas
|
|
Tropical
Montane Forest
|
- Changes
in degree of cloud cover versus and sunlight hours
- Hurricane
frequency and severity
- Drought
frequency and annual rainfall distribution
|
- Drying
out and invasion or replacement of montane species by lower montane
or non-montane species
|
|
|
| Boreal
Forest |
- Mean
annual temperature
- Fire
frequency and severity
- Storm
frequency and severity
- Growing
season length
- Increases
in pest attack
|
- Significant
losses in some areas, mainly through fires and pest attack. Expansion
of boreal forest into Arctic areas
|
|
|
|
Arctic habitats
|
- Mean
annual temperature
- Season
length
- Precipitation
|
- Vegetation
changes with vast losses of tundra and forest extension
- Thawing
of permafrost leading to additional release of soil carbon as
CO2 in a positive feedback loop
|
|
Alpine / Mountains
|
- Mean
annual temperature
- Snow
fall and melt
- Growing
season length
|
- Altitudinal
migration of habitats, with invasion of alpine meadows by forest
systems, highest altitude habitats may be unable to migrate
|
|
|
|
Low-lying islands
|
- Relative
sea-level rise
- Storm
frequency and severity
|
- Loss
of land area, seabird nesting colonies. Increased human demands
on remaining terrestrial habitats
|
|
Arid and semi-arid areas
|
- Precipitation
patterns
- Minimum
winter temperatures
|
- With
a few exceptions deserts are expected to become hotter and drier
- Desertification
into sub-Saharan Africa and Central Asian Steppes
- Salinisation
- Loss
of grassland
- Loss
of arable land
|
|
Coral Reefs
|
- Sea-surface
temperature, indirect chemical effects of higher CO2 concentrations
in the water
|
- Prolonged
exposure to even minor (>1ºC) rises in temperature causes coral
bleaching and may result in coral death
- Impacts
may be compounded by chemical effects of increasing CO2 concentrations
which could reduce calcification rates (skeletal development,
growth rate).
|
|
Mangroves
|
- Relative
rate of sea-level rise, changes in hydrological balance in estuarine
systems
- Storm
frequency and severity
|
- Decrease
in extent as coastal zone becomes "squeezed" between
sea and inland agriculture
|
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