Natural variability in our climate
Large-scale climate processes, such as the El Niño – Southern Oscillation (ENSO), the Indian Ocean Dipole (IOD) and the Southern Annular Mode (SAM), affect Australia’s climate in cycles. These processes change Australia’s climate by moving warm water and warm, moist air to different regions.
El Niño – Southern Oscillation
ENSO has 3 phases: El Niño, La Niña and the neutral phase. During the neutral phase, the trade winds of the Pacific Ocean blow warm, moist air and warm waters towards north-eastern Australia. The warmer waters cause air to rise, creating rainfall. During La Niña, these winds get even stronger, increasing the amount of warmer water near Australia, increasing the rainfall and causing floods. During El Niño, these winds weaken, or even reverse, moving warm water away from Australia and towards South America. With less warm water, rainfall is less likely to form and hence Australia often experiences drought.[1]
Indian Ocean Dipole
During the positive phase of the IOD, the eastern Indian Ocean experiences lower than normal sea-surface temperatures compared with the western Indian Ocean. Warmer waters in the west cause more rain over Africa and there is less rainfall in Australia and parts of southern Asia. During the negative phase of the IOD, these conditions are reversed and Australia is cooler and wetter.[2]
Southern Annular Mode
SAM refers to north-south changes in Antarctica’s strong westerly wind belt. SAM affects rainfall in different regions of Australia depending on the phase (positive, neutral or negative) and the season.[3] During the negative phase, the westerly winds move closer to Australia. This brings more low-pressure systems to southern Australia, and areas such as Victoria experience more rain and storms. During the positive phase, the westerly winds move further south, so high-pressure systems form over southern Australia, leading to drier, more stable weather.[4] SAM phases are usually quite short, lasting from a week to a few months.
Into the future
Under a changing climate, SAM is predicted to spend more time in the positive phase, bringing drier weather to parts of southern Australia during winters, and wetter conditions during summer in south-eastern Australia and eastern Tasmania.[5]
Increasing surface temperatures mean that a typical La Niña year now is warmer than El Niño years were back in the 1980s.[6] ENSO events are likely to increase in amplitude and frequency due to climate change, having stronger effects and occurring more often.[7] [8] This may result in more flooding in some Pacific Island nations and more drought elsewhere, such as mainland Australia.[9] Even if we keep global warming to 1.5 °C, we still expect extreme ENSO events to persist for another 100 years or so.[10]
Extremely positive IOD events are likely to increase as climate changes.[11] These events tend to correspond with El Niño events, bringing more drought to Australia.[12] Limiting global temperatures would have an immediate effect on halting the increased frequency of extreme positive IOD events.[13]
Useful links
- Agriculture Victoria - the six drivers that influence Victoria's climate
- Bureau of Meteorology - three phases of El Niño – Southern Oscillation
- Bureau of Meteorology - Indian Ocean Dipole
- National Environmental Science Program - managing climate variability and extremes
- Bureau of Meteorology - Southern Annular Mode
- Bureau of Meteorology - Southern Annular Mode and the Australian climate
References
- The three phases of the El Niño–Southern Oscillation (ENSO)
- The Indian Ocean Dipole (IOD)
- Southern Annular Mode and the Australian climate
- The Southern Annular Mode (SAM)
- Southern Annular Mode: The climate 'influencer' you may not have heard of
- State of the Climate 2020 [PDF · 6.5MB]
- El Niño-Southern Oscillation: five things to know about this climate phenomenon
- Science update: What does the future hold for El Niño-Southern Oscillation and the Indian Ocean Dipole?
- Science update: What does the future hold for El Niño-Southern Oscillation and the Indian Ocean Dipole?
- Extreme El Niño events to stay despite stabilisation
- Indian Ocean Dipole linked to global warming in new research by Australian scientists
- The Indian Ocean Dipole (IOD)
- Science update: What does the future hold for El Niño-Southern Oscillation and the Indian Ocean Dipole?
Natural variability in our climate
Large-scale climate processes, such as the El Niño – Southern Oscillation (ENSO), the Indian Ocean Dipole (IOD) and the Southern Annular Mode (SAM), affect Australia’s climate in cycles. These processes change Australia’s climate by moving warm water and warm, moist air to different regions.
El Niño – Southern Oscillation
ENSO has 3 phases: El Niño, La Niña and the neutral phase. During the neutral phase, the trade winds of the Pacific Ocean blow warm, moist air and warm waters towards north-eastern Australia. The warmer waters cause air to rise, creating rainfall. During La Niña, these winds get even stronger, increasing the amount of warmer water near Australia, increasing the rainfall and causing floods. During El Niño, these winds weaken, or even reverse, moving warm water away from Australia and towards South America. With less warm water, rainfall is less likely to form and hence Australia often experiences drought.[1]
Indian Ocean Dipole
During the positive phase of the IOD, the eastern Indian Ocean experiences lower than normal sea-surface temperatures compared with the western Indian Ocean. Warmer waters in the west cause more rain over Africa and there is less rainfall in Australia and parts of southern Asia. During the negative phase of the IOD, these conditions are reversed and Australia is cooler and wetter.[2]
Southern Annular Mode
SAM refers to north-south changes in Antarctica’s strong westerly wind belt. SAM affects rainfall in different regions of Australia depending on the phase (positive, neutral or negative) and the season.[3] During the negative phase, the westerly winds move closer to Australia. This brings more low-pressure systems to southern Australia, and areas such as Victoria experience more rain and storms. During the positive phase, the westerly winds move further south, so high-pressure systems form over southern Australia, leading to drier, more stable weather.[4] SAM phases are usually quite short, lasting from a week to a few months.
Into the future
Under a changing climate, SAM is predicted to spend more time in the positive phase, bringing drier weather to parts of southern Australia during winters, and wetter conditions during summer in south-eastern Australia and eastern Tasmania.[5]
Increasing surface temperatures mean that a typical La Niña year now is warmer than El Niño years were back in the 1980s.[6] ENSO events are likely to increase in amplitude and frequency due to climate change, having stronger effects and occurring more often.[7] [8] This may result in more flooding in some Pacific Island nations and more drought elsewhere, such as mainland Australia.[9] Even if we keep global warming to 1.5 °C, we still expect extreme ENSO events to persist for another 100 years or so.[10]
Extremely positive IOD events are likely to increase as climate changes.[11] These events tend to correspond with El Niño events, bringing more drought to Australia.[12] Limiting global temperatures would have an immediate effect on halting the increased frequency of extreme positive IOD events.[13]
Useful links
- Agriculture Victoria - the six drivers that influence Victoria's climate
- Bureau of Meteorology - three phases of El Niño – Southern Oscillation
- Bureau of Meteorology - Indian Ocean Dipole
- National Environmental Science Program - managing climate variability and extremes
- Bureau of Meteorology - Southern Annular Mode
- Bureau of Meteorology - Southern Annular Mode and the Australian climate
References
- The three phases of the El Niño–Southern Oscillation (ENSO)
- The Indian Ocean Dipole (IOD)
- Southern Annular Mode and the Australian climate
- The Southern Annular Mode (SAM)
- Southern Annular Mode: The climate 'influencer' you may not have heard of
- State of the Climate 2020 [PDF · 6.5MB]
- El Niño-Southern Oscillation: five things to know about this climate phenomenon
- Science update: What does the future hold for El Niño-Southern Oscillation and the Indian Ocean Dipole?
- Science update: What does the future hold for El Niño-Southern Oscillation and the Indian Ocean Dipole?
- Extreme El Niño events to stay despite stabilisation
- Indian Ocean Dipole linked to global warming in new research by Australian scientists
- The Indian Ocean Dipole (IOD)
- Science update: What does the future hold for El Niño-Southern Oscillation and the Indian Ocean Dipole?
Related to this page
- Climate dogs - the six drivers that influence Victoria's climate
- BOM: What is the Indian Ocean Dipole
- Managing climate variability and extremes
- BOM: What so the Southern Annular Mode
- BOM: Southern Annular Mode and the Australian climate
- BOM: State of the Climate [PDF · 6.5MB]
- Understanding the present and future dynamics of ENSO and IOD
- Blog: El Nino southern oscillation
- Extreme El Nino events to stay despite stabilisation
- Reading the Indian Ocean