Understanding climate definitions

Weather is what we experience on a daily basis — sunshine, rain, wind. It is today and tomorrow and what a fisher looks at when deciding what they will do that day. The Bureau of Meteorology produces very accurate 4 day weather forecasts and is starting to deliver accurate 7 day weather forecasts for all of Australia and its waters.

Climate variability is what you expect to experience over a longer period of time — more rainfall and floods or less rainfall and drought — with the resulting flow-on impacts on the environment and fish stocks.

Climate change is a shift in the baseline pattern of climate variability. The projections for increasing global air and ocean temperatures are well documented.

Climate drivers across Australia – all operate at differing time and spatial scales and have differing levels of impact across Australia. It is not only the strength of each climate driver, but the combination and interaction between them that dictates our weather and the level of climate variability we see. There are multiple permutations of these interactions that make forecasting climate a complex and diffi cult task. More accurate climate forecasting is becoming achievable through the array of satellites and ocean buoys that have been placed worldwide and the data received being coupled with high powered computer driven climate models.

There are a number of climate drivers that influence weather patterns in Australia (and rest of the world). For example:

  1. El Niño/La Niña Southern Oscillation — the temperature range that occurs in the Pacific Ocean over a number of years. This system influences climate and generally leads to wetter or drier conditions across most of eastern Australia.
  2. Indian Ocean Dipole — the temperature range that occurs over a time scale of months to years in the Indian Ocean. This system influences the climate across western and northern Australia.
  3. Southern Annular Mode — the temperature and pressure ranges associated with the Southern Ocean, with varied time scales (both short and long term). This system generally brings rain to southern Australia when it is in its northernmost phases.
  4. Madden-Julian Oscillation — the system pulses in waves with eight distinct phases. The system moves across the Indian Ocean towards the Pacific Ocean and influences particularly tropical Australia.
  5. The Monsoon phase — this moves between the northern and southern hemisphere across the equator on an annual basis. This accounts for a large part of driving the ‘wet season’ in northern Australia and its intensity is strongly linked to the interactions between the El Nino / La Nina Southern Oscillation, the Indian Ocean Dipole and the Madden Jullian Oscillation.
  6. Cloud bands — these start in mid North West Australia and move South East. They bring high and low pressure changes and determine available moisture.
  7. Frontal changes — these start in the south west moving towards the south east and Southern  Indian Ocean. They bring rain and wind.

Overlying this complex pattern of climate variability is climate change. The world’s climate continues to change — just as it has for millions of years (with ice ages and warmer cycles). We now understand global climate systems enough to make a distinction between what is natural climate change and what change can be attributed to human impacts altering the composition of the earth’s atmosphere.

Industrialisation, burning fossil fuels, land clearing and the loss of wetlands are some of the factors that lead to increased greenhouse gas pollution and have affected the dynamics of the planet and its atmosphere — or put simply how the earth naturally heats and cools. More information about Understanding climate change is available on the Department of Environment website.

Increased production of greenhouse gases, such as carbon dioxide and nitrous oxide, when released into the atmosphere increase the effective thickness of the “earth’s blanket’, the atmosphere, trapping more radiation from the sun, heating up the planet and causing what is termed as the greenhouse effect.

Global average temperatures have risen over the past century — and at an increasing rate.

It is predicted that climate change will contribute to more extreme weather events (e.g. drought, severe storms, high sea levels, floods). Actual influence of climate change on extreme events is still being quantified.  For example, it is predicted Australia will continue to see tropical cyclones build in northern Australia. These cyclones are predicted to be of similar frequency, but they will become more intense. Australian fisheries have already seen and know what to expect after tropical cyclone Hamish swept across the Great Barrier Reef in March 2009 — see FISH Article 19-2 Trout Turn Tail in Wake of Hamish [PDF]. Hamish surpassed all previous storms in intensity, duration and track length over coral reef structure.