Climate change

Global climate change, caused by an enhanced greenhouse effect, will affect the natural environment in Australia and NSW.

Annual average temperatures in Australia are projected to increase by 0.4-2.0oC by 2030 and by 1-6oC by 2070 compared to 1990 levels. While it is generally not known what changes will occur at a regional level or for specific ecosystems, some changes are widely accepted. These include:

  • Increased average temperatures

Of particular concern for fish is the increase in minimum temperatures and the potential for more extreme temperature events. This will affect habitat availability, water quality and change the seasonal temperature cures some native fish rely on to begin migration or spawning.

  • Increased variability in rainfall

Australia’s rainfall patterns are naturally variable, however, changes in the patterns of where, when and for how long rain falls will affect native fish. Many areas will experience more frequent and more serious drought, limiting fish habitat availability.

  • Increased rate of change in habitat condition

Plants and animals can adapt to changing conditions provided the rate of change is not too fast. The current rate of change is expected to increase. This, coupled with the pressures fish habitats are already under, poses a serious risk to the long term viability of native fish.

While temperature and rainfall are important cues for fish migration and breeding, some of their important food sources, such as insects and other invertebrates, often use day length as a cue for hatching. With relatively rapid changes in temperature and water flows, the cues that fish respond to may not coincide with an abundance of food.

Fish may be able to respond to the expected changes and move to more favourable habitats provided that such habitat areas exist and there are aquatic corridors that connect them. If waterways are effectively blocked by dams or weirs or a lack of water or there are long stretches of unsuitable habitat, native fish will not be able to move to more favourable habitat.

Climate change will also affect transitional habitats, such as the estuaries that are so important for NSW commercial and recreational fishing. Changes to the volume and timing of water flowing into the estuaries from coastal rivers will have potentially catastrophic impacts on fish migration, habitat use, breeding and food availability. Rising sea levels will also impact estuaries, with some areas becoming permanently inundated.

The impacts of climate change on marine habitats and fish are less clear. It is expected that:

  • temperature both at the surface and at depth will increase,
  • greater stratification which will reduce nutrient input into shallower waters,
  • surface winds will increase and
  • the strength of surface currents will decrease.

A relative lack of knowledge about marine species and ecosystems and their interaction with global oceanographic and atmospheric systems means that it is difficult to predict impacts on specific species or fisheries. However, longer term changes affecting just two key factors, ocean temperatures and nutrients, will have a significant influence on marine biodiversity. The predicted impacts include:

  • effects on distribution and stocks: species are generally expected to move southward with warming; species such as pteropods reliant on building shells are likely to decline in abundance
  • effects on the timing of life cycle events: the timing of blooms and migrations are expected to occur earlier with warming
  • effects on physiology and behaviour: environmental change will directly affect rates of metabolism, reproduction, development, photosynthesis and respiration
  • effects on communities and productivity: this is dependent on the place of the species in relation to ecosystem functioning, for example the place of a species in the food chain.

What is the greenhouse effect?

The earth’s climate is controlled by energy from the sun that is absorbed by the earth’s atmosphere. A blanket of naturally occurring “greenhouse gases” trap heat in the atmosphere and create what is commonly referred to as the ‘greenhouse effect’.

Without this blanket of heat-trapping greenhouse gases (including water vapour, carbon dioxide, methane, and nitrous oxide) the earth’s average temperatures would be around 34°C colder.

But since the Industrial Revolution human activity has increased the concentration of greenhouse gases in the atmosphere. This includes both naturally occurring greenhouse gases such as carbon dioxide, methane and nitrous oxide, as well as a number of man-made greenhouse gases such as sulphur hexafluoride, perfluorocarbons and hydrofluorocarbons. Most importantly, since the Industrial Revolution the atmospheric concentration of carbon dioxide has increased by 35% and it is now the highest it has been for the past 420,000 years.

Concentrations of other greenhouse gases are also on the rise, such as methane, which has risen by 151%.

The Intergovernmental Panel on Climate Change, established by the World Meteorological Organisation and the United Nations Environment Program, has concluded that human activities which increase greenhouse gas concentrations are “enhancing” the natural greenhouse effect and resulting in a changing climate.

If concentrations of greenhouse gases continue to rise, the resulting climate change will have significant impacts on agriculture, water supply, infrastructure, biodiversity and human health.

Source: NSW Greenhouse Plan 2005.

See also