Understanding climate processes improves our ability to model Australia’s climate.
Improving our understanding of ocean, land, ice and water cycle processes leads to greater confidence in climate models, as the physical mechanisms of their behaviour can be better replicated.
Knowledge of climate processes helps scientist to recognise the difference between climate variability and climate change. Studying large-scale features of the climate such as the El Niño-Southern Oscillation (ENSO), Indian Ocean Dipole and the Southern Annular Mode, including their interactions, helps us predict how these patterns may change in a warmer world.
A number of elements affect the climate system including the behaviour of clouds, aerosols and winds; interactions between ocean, sea-ice and ice sheets; ocean currents; and the balance of carbon in land, air and oceans. ACCSP scientists study these elements to improve projections of our future climate.
The El Niño-Southern Oscillation (ENSO), Indian Ocean Dipole and the Southern Annular Mode are major drivers of climate variability over Australia. They contribute to conditions that lead to major bushfires, droughts and floods. Understanding the processes by which these drivers influence climate is an active area of research.
ENSO also affects southern Australian rainfall. When an El Niño occurs, southern Australia tends to be drier than normal. ACCSP research shows that the ENSO influence on southern Australia occurs through the Indian Ocean via a large atmospheric wave structure known as a Rossby wave train. Previously, the process by which an El Niño causes drier conditions in southern Australia had not been well understood.
Scientists have shown that the Indian Ocean Dipole influences south-east Australia’s climate predominantly during winter and spring. When the tropical eastern Indian Ocean is cooler than normal and the west is warmer than usual it leads to higher temperatures and lower rainfall across southern Australia in winter and spring.
The Southern Annular Mode (SAM) is a climate driver that influences southern Australian rainfall. SAM is a measure of the strength and position of the westerly winds that circulate around Antarctica.
When SAM is in a positive phase the polar westerly winds speed up causing low pressure systems and cold fronts to contract towards the South Pole. Generally a positive mode will result in fewer winter rain bearing frontal systems across the southern coastal region of Australia. A negative phase SAM involves low pressure systems circulating closer to southern Australia. This results in more cold fronts sweeping up into southern Victoria in winter increasing the chance of rainfall.
ACCSP research found that although the Southern Annular Mode (SAM) influences winter rainfall in southern Australia, the SAM has no impact on the autumn rainfall reduction over southeast Australia. A poleward expansion of the subtropical dry-zone is partly responsible.
Future emissions will have a strong impact on the climate of the Southern Hemisphere. ACCSP research has found that the recovery of the Antarctic ozone hole will counteract some of the impacts of Southern Hemisphere climate change in summer, especially under low-emissions scenarios (under 2 °C warming). For high-emissions scenarios the greenhouse gases dominate the climate change response with ozone playing only a minor role. Increasing greenhouse gas emissions are likely to affect SAM, lowering rainfall across southern Australia in winter.
The interactions between ozone, greenhouse gases and SAM are complex, and ACCSP scientists are continuing to find out more about SAM’s behaviour.