The climate is a crucial factor in determining where animals and plants live and reproduce, and the types of ecosystems they form (IPCCb, 2001). Nature is always changing, and at different stages of the earth’s history, the places we know and appreciate today would have looked quite different or not existed (IPCCb, 2001).
The human-induced climate change that is occurring now will also trigger much more rapid changes, however this period of change may prove to be deadly for many species. The change we are causing to the world’s climate is potentially more dramatic and disruptive than ever before.
While some Australian animals and plants are adapted to withstand dramatic seasonal changes in climate each year, many species have quite limited ranges of long-term average climate. Temperature ranges in the order of 1 – 2°C and 20 percent variation in rainfall mean that Australian animals and plants are vulnerable to long term climate change (Pittock and Wratt 2001).
Climate change could have a greater impact on species than all human interventions to date.
Climate change affects ecosystems and wildlife in several key ways:
Inability to keep pace with changing times
Wildlife moves if possible towards preferred climate conditions for breeding, nesting, growing or feeding. With the temperature increases expected over the next 100 years, many plants and animals will need to be on the move.
A 3°C change in mean annual temperature (middle of the predicted temperature range over the next 70 years) corresponds to a shift of approximately 300 – 400 km in latitude (in the temperate zone globally) or 500 metres in elevation (Hughes 2000). Some species that are sensitive to change will need to move away from their hotter home ecosystem southwards to where their preferred climate will exist in the future. Other species may be able to adapt to the new climate conditions at their current location and will become more dominant.
An important global study commissioned by WWF attempted to gain a broad worldwide picture of the climate changes that ecosystems may need to adapt to. The study was based on a conservative estimate of CO2 doubling (from pre-industrial levels by 2100), and then modelling the rate that 10 vegetation types across the world would need to move to stay within their usual climatic range.
The study found that “very high” migration rates (greater than or equal to 1 km/year) were relatively common, comprising on average 17 – 21 percent of the world’s land surface. This rate of movement is deemed to be “very high” because migration rates greater than this are very rare in fossil records recording change from a glacial to a non-glacial period (Malcolm and Markham, 2000).
The same study identified where vegetation types will change with the climate, leading to loss of existing habitat (see map). Although some type of vegetation will persist under these new conditions, it may be unsuitable habitat for existing plant and animal species. The study found significant changes to the existing habitat of 35 percent of the land area of the world with moderate levels of climate change. This is in addition to the habitats already seriously impacted by human activities, comprising 20 percent of the total land area. These results suggest that climate change could have a greater impact on species than all human interventions to date (Malcolm and Markham, 2000).
Barriers to movement
Even when past climate change has occurred over several thousand years, some species have not be able to adapt rapidly enough. High species richness appears to be related to stable conditions, and impoverishment of species has occurred during times of rapid change (IPCCb, 2001). The shifts imposed by human-induced global warming will occur within 100 years and this may exceed the capabilities of many species (Malcolm and Markham, 2000).
While some species find it difficult to move (eg. rainforest species), others are more adaptable (eg. weeds) and in normal conditions may have an ability to migrate. However, there are a second layer of barriers for these more adaptable species. Tree populations of a forest may expand or contract towards a more suitable climate but then be stopped by a body of water, unsuitable soils or a city or farm. Species that might otherwise be able to adapt to climate change will be in trouble because the natural environment is now fragmented by human settlement (IPCCb, 2001)
A tougher environment - climate change suits some species and not others
Species that can tolerate a changed climate will take the place of those species that are sensitive to change. Some species will decline in abundance or become extinct, others will increase in abundance. Within the predicted temperature changes over the next 50 years, Australian environments will be very different from those we see today.
“Weedy” species with fast growth rates and a strong ability to disperse will be advantaged (Hughes, 2000; Pittock and Wratt, 2001). Species with small populations, restricted ranges and specific habitat requirements are the most vulnerable to climate change and most likely to be disadvantaged (IPCCb, 2001; Chapman and Milne, 1998). The new ecosystems that emerge, made up of plants tolerant to climate change, may not provide suitable habitat for the animals that have lived in that area in the past.
Effects on physiology
Changes in temperatures and rainfall, and increases in CO2, directly affect the metabolism and rates of development in animals, and rates of growth and photosynthesis of plants (Hughes 2000).
Effects on relationships and behaviors
Many animals and plants depend on each other for survival, and changes in one species may affect another. For example, plants and birds need and use each other for food, shelter, pollination and seed dispersal. Climate changes which, for example, cause earlier flowering times, will disrupt these dependence relationships between partner species (Hughes, 2000).
Secondary effects of climate change
In Australia, climate change is projected to see decreases in winter rainfall across much of southern Australia, the potential for more bushfires and more intense cyclones (CSIRO, 2001). These changes will have an indirect negative impact on plants and animals already under stress from land degradation and changing climatic conditions.
For example, death of trees in Western Australia due to a reduction in rainfall will have a marked longer term impact on the populations of those bird species that breed only in tree hollows, such as cockatoos, corellas, galahs, parrots and lorikeets (Arnold 1988).
Great Barrier Reef
Image courtesy of World Wide Fund For Nature
Percentage loss of existing habitat that could occur with a doubling of CO2 concentrations in the atmosphere.
Image courtesy of WWF