TRANSCRIPT
NARRATION
In the Bay of Bengal off the coast of India, a slight shift in the surface temperature of the sea brews a massive cyclone. Low-lying Bangladesh is right in its path. Coastal communities are smashed, millions of people devastated. While thousands of kilometres away on the other side of the planet…
FARMER
It’s just another dry spell, I think. We’re hoping it is anyway.
NARRATION:
Australian farmers feel the lifeblood of their land slip through their fingers…
FARMER
It’s just got that hard now, it’s nearly impossible to do.
NARRATION
And we watch in horror as parched bushland explodes.
MARK HORSTMAN
The drought is so severe, the bush fires so vicious, it seems the climate is conspiring against us. This is a story of cause and effect, how a small change in a far off ocean triggers a big dry in Southern Australia, with no end in sight.
NARRATION
Climate scientists are scrambling to explain why Victoria remains locked in drought after nearly fifteen years.
PROF. MATTHEW ENGLAND
Everybody in the climate science community has been looking at that drought and wondering why it hasn’t broken.
DR SUSAN WIJFFELS
Unfortunately rainfall distribution and changes in rainfall is one of the areas where I think the climate science is still struggling.
DR SCOTT POWER
Not only are natural processes at play here, there may also be another factor which is global warming.
NARRATION
In the Pacific Ocean, the La Nina weather pattern brings rain to Australia as trade winds push warm water to our side of the ocean. Every two to seven years, its counterpart El Nino relaxes or even reverses the trade winds, drawing the warm water and the rain clouds away. Over the last 60 years, our rainfall has been reduced with more El Ninos and fewer La Ninas.
In the Southern Ocean, a massive vortex of high speed winds circling Antarctica spins off cold fronts that feed winter rain to the southern fringes of Australia. But as global warming contracts the vortex, the rains are dragged further south and miss the land. But neither can completely explain the Big Dry. As science races to beat the breaking wave of climate change, new research has found an unexpected culprit.
PROF. MATTHEW ENGLAND
When the La Ninas came along in the last few years, pretty much every climate scientist including myself thought that it would bring drought breaking rains to the whole eastern seaboard. That didn’t go as far down as Victoria and that surprised a lot of people.
NARRATION
Instead of the Pacific or the Southern Oceans, climatologist Matt England and his team are looking to the Indian Ocean for answers.
PROF. MATTHEW ENGLAND
And you can actually see with this graphic, the influences of each of those basins. You can see cloud bands coming down from the Indian Ocean, occasionally bringing relief with good rain systems.
MARK HORSTMAN
Is that one there now?
PROF. MATTHEW ENGLAND
Yeah that’s exactly right. Every winter, if not enough of them come through then clearly you start to get into a drought phase.
NARRATION
Whether the cloud bands from the north-west make it to Victoria depends on how the sea temperatures spread across the surface of the Indian Ocean.
MARK HORSTMAN
Tonight’s weather report is brought to you courtesy of the Indian Ocean Dipole, that’s the technical term for a rain making cycle in the Indian Ocean that drives drought conditions in Southern Australia.
NARRATION
When the Indian Ocean is cooler in the west and warmer in the east, this generates winds that sweep rain clouds towards Australia. This is the negative or warm phase of the dipole. But in its positive cool phase, the sea temperatures are reversed, the winds move away from Australia, and the rains don’t come.
PROF. MATTHEW ENGLAND
Our research showed that it’s in fact the Indian Ocean temperatures that are conspiring to not give us drought breaking rains down in South-Eastern Australia.
NARRATION
To understand why, we need to find what causes those temperatures to change. The answer lies in the waters swirling around the myriad islands of the Indonesian archipelago. Susan Wijffells drops expensive equipment like this into deep water and raging currents to unravel the secrets of how oceans transfer energy. In 2005, she led the first oceanographic team to map the currents of the Indonesian Throughflow, where the Pacific and the Indian Oceans meet.
DR SUSAN WIJFFELLS
One of the really new things was the strong variability that we saw. And so we were surprised by this because we always thought the Pacific was really the ocean that was driving the variability of this set of currents. But what we really found was that the Indian Ocean is actually really really powerful in driving this current system as well.
MARK HORSTMAN
Let’s say this is the Pacific Ocean and that’s the Indian Ocean and this is the narrow choke point where they meet, the so called Indonesian Through-Flow. Now the water rushing through is incredible, around about 60 million bath tubs full of water every second.
DR SUSAN WIJFFELS
The flow is coming in through here, through Lombok, Ombai, and Timor. And that warm flow drives this guy, this is the Leeuwin current, you can see the turbulent Leeuwin Current, which actually comes all the way around through the Bight and right around to Tasmania. That’s all being driven by that leakage of warm water from the Pacific.
The winds blowing along the equator just pile up a vast amount of water in the Western Pacific and that basically just raises the ocean pressure and that drives the current through the Indonesian archipelago right into the Indian Ocean. It radically changes the climate, especially for Western Australia. Western Australia would be a very cold desert if it wasn’t for this leakage of warm water.
NARRATION
This battle between two oceans for control of the atmosphere is what switches the Indian Ocean Dipole between its cool positive phase and its warm negative one.
DR SUSAN WIJFFELS
During the cold phase of the dipole, those local winds are winning the battle and they drive lots of upwelling and they cool off the surface temperature, it dries out the atmosphere and dries out Australian climate.
What this Indonesian Throughflow, this water coming in from the Pacific is doing is it’s competing with the local winds. And it’s trying to kill the dipole, trying to flood the area with warm water and make the atmosphere moist and energetic again and make a wetter climate for Australia.
NARRATION
But in these natural cycles, Susan sees the signs of climate change.
DR SUSAN WIJFFELS
We think we see a weakening of this set of currents. The Pacific trade winds might be weakening. The Indian Ocean might be drifting into a more of a permanent dipole state so that the cold phase, which is the phase that dries out Australia, might be becoming more frequent.
NARRATION
That fits with what Matt found when his team analysed the climate data from Australia’s worst droughts.
PROF. MATTHEW ENGLAND
When we looked at the sea temperature patterns, all of the reconstructions for sea temperature right back through the last century showed that these droughts that were occurring over these decade long periods had one thing in common and that is that they all lacked a negative phase of the Indian Ocean Dipole.
NARRATION
This graph shows the three big droughts of the last 130 years: the Federation drought, the World War II drought, and the most severe of all, the current Big Dry. The red bars are negative phases of the Indian Ocean Dipole that bring rain – and what’s important here is they’re lacking from every single drought.
PROF. MATTHEW ENGLAND
For the last fifteen years there have been no negative phases of the Indian Ocean Dipole. That’s unprecedented.
NARRATION
On top of that, air temperatures over the continent have risen by nearly one degree.
PROF. MATTHEW ENGLAND
It doesn’t sound like a lot but that’s enough to push the land to a much drier, moisture depleted state.
NARRATION
But not everyone is convinced that the Indian Ocean should cop all the blame for the drought in Victoria.
DR SCOTT POWER
We know that the Indian Ocean Dipole events only occur in about one in four years, so that obviously leaves three in four years in which Indian Ocean Dipole events can’t explain rainfall changes. What we’re concerned about is the fact that global warming is starting to influence Australian climate and sea surface temperatures.
NARRATION
Using statistics from weather in the past cannot forecast a future where climate change shifts the ground rules.
DR SCOTT POWER
We are putting much greater emphasis these days into developing computer based dynamical models of the climate system. So they don’t use statistics, they actually look at the physics of the climate system.
PROF. MATTHEW ENGLAND
We are all across this question trying to work out how the Indian Ocean interacts with the Pacific and the Southern, how they all combine to affect Australian rainfall. It’s the next thing to answer.
NARRATION
But weakening trade winds, rising temperatures, and shifting weather patterns have already stolen the reliable rain from our nation’s food bowl.
MARK HORSTMAN
Over the last century the positive dipole events that bring drought to southern Australia have tripled in number, and as if that’s not enough, it’s predicted that as the world warms over the next one hundred years they’ll increase by another 20 per cent.
DR SUSAN WIJFFELS
We are moving our climate system and we still don’t have a really good grip on how fast the thing is going to move. We need to really be keeping track of the system so that our children really do have a proper understanding of what’s going on and they’re not dealing with an inadequate set of information the way we are.
• Watch Prof. Matthew England's extended interview here
• Watch Dr Scott Power's extended interview here
• Watch Dr Susan Wijffels' extended interview here
- Reporter: Mark Horstman
- Producer: Max Lloyd
- Researcher: Anja Taylor
- Camera: David Hudspeth
Kevin May - Sound: Steve Ravich
Dave Harper - Editor: Sasha Madon
Story Contacts
Prof Matthew England
Climate Change Research Centre
Level 4, Matthews Building
Faculty of Science
University of NSW
Sydney NSW 2052
Dr Susan Wijffels
Research Oceanographer
CSIRO Marine Research
GPO 1538
Hobart Tas 7000
Dr Scott Power
Principal Research Scientist
Centre of Australian Weather and Climate Research
Bureau of Meteorology
GPO Box 1289, Melbourne VIC 3001
Related Info
Indian Ocean Dipole website, Japan Agency for Marine-Earth Science and Technology
Climate Change Research Centre, UNSW
“What causes southeast Australia’s worst droughts?”, Geophysical Research Letters, 2009
News story: Bushfires linked to IOD, 25 March 2009
Triggering of the positive Indian Ocean dipole events by severe cyclones over the Bay of Bengal
“Lessons from a distant monsoon”: Nature, 2007
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YOUR COMMENTS
Comments for this story are closed. No new comments can be added.
- 14 Dec 2009 7:29:32pm
FOR AUSTRALIAN CLIMATE MODIFICATION.
Erosion trigger channel +
huge tides = huge erosion of
land tidal channels = desert land desalination
= more clouds = more rain
= cooler climate = huge carbon sink
see:
http://www.royalcommission.vic.gov.au/Submissions/SubmissionDocuments/SUBM-002-010-0001_R.pdf
http://www.climatechange.gov.au/en/submissions/cprs-green-paper/~/media/submissions/greenpaper/0929-mitic.ashx
- 29 May 2009 3:06:03pm
The narrator says that air temperatures over Australia have risen by 1 degree. Over what period has that rise occurred and has any consideration been given to the urban heat island effect. Also it is said by many that the cooling over that last seven or so years has negated the rise from 76 to 98. Is Australia different?
- 02 Jun 2009 10:40:33am
Forget about tracking year to year temperature fluctuations, it's a furphy inserted in to the argument by "skeptics" (people with a vested interest in maintaining fossil fuel consumption). Instead, understand the physics: a greenhouse gas allows high frequency radiation to pass but reflects low frequency. Incident energy from the sun is predominantly high frequency, so it passes to the surface of the earth, where it is reflected as predominantly low frequency, so it is reflected back to earth instead of passing back out to space. This is exactly the same as a greenhouse, or a car, where glass is the medium acting as the the energy passer/reflector causing the greenhouse effect.
Once you understand the physics you understand that doubling (or more) the concentration of CO2 in the atmosphere can only go one way for earth's surface temperatures over time.
As for Bill's question below - no one knows, but the change in atmospheric composition being brought about by human activities is of the same order of magnitude as previous catostrophic meteorite strikes and volcanic upheavals, which led to dramatic climate change and consequent mass extinctions and loss of biomass, so draw your own conclusions.
- 03 Jun 2009 10:14:45am
Australian annual mean temperatures have increased by approximately 0.9°C since 1910, consistent with a global mean temperature increase of between 0.7°C and 0.8°C since 1900. (Bureau of Meteorology, 2006)
- 29 May 2009 12:30:59pm
But the story still didn't address the question: To what extent are these water and air flows affected my man's actions?????"
- 28 May 2009 11:59:20pm
I recall seeing on Al Gore's "Inconvenient Truth" Documentary that his most dire warning is the ocean current flow changes that will melt Greenland and eventually send us into an ice-age. That is after we all melt first. This may be showing some effect already.
- 28 May 2009 11:01:42pm
There seems to something odd about the way we understand our weather. I have read weather maps for a long time now, 50 years or so, and it struck me that the rain in south east Australia came in on the lows that swept across on the roaring forties. In summer they moved south, pushed by the inland high pressure systems moving south over the Bight. Now the highs stay over the Bight. This seems to mean either that the lows are being pushed further south or that they have moved south and the highs have moved to fill the space (so to speak). We used to get summer rain on upper level troughs coming in from the tropics either as the tail of a cyclone or as a low in the north connecting to one in the south. A couple of these have occurred in recent years which have dumped heavy falls on Victoria, especially in the summer of 2005 (Feb) and 2007 (Dec). I think the IOD is an interim explanation that hardly explains the problem in the south because we still get most of our (SA and Vic) rain from the south west. And how does the IOD exlain the wetter north west? I wonder whether the Leeiwin current isn't hotter and is pooling in the Bight, the sea surface temp maps on BOM site suggest they do. This would strengthen the highs over the Bight. What about cyclonic activity? Is there a relationship between number and intensity of cyclones in the north and rainfall in the South east; almost no cyclones have crossed the land this last season? El nino was a dud explanation for this part of the world from the word go because it overlooked what happens this far south, so does that mean El nino events and IOD events coincide to put the whole of eastern Australia into drought? And what about tree cover? And the ABC-Asiatic Brown Cloud, how is that effecting our weather? If, as reported on the news tonight, the bushfires pushed smoke into the atmosphere over the Antarctic, does this mean it will cool as it does when we get a big volcanic eruption like Mt Pinatubo, or Mt Erebus in the Antarctic, which is always gassing? And then there is the SAM, why didn't the item mention the Southern Antarctic Mode? Surely that has some effect. Also is the IOD effected by the Atlantic Conveyor system which ends up in that ocean? Is it a driver of the IOD too? In which case the Bermuda triangle reaches out into the 4 corners of the world?
One problem with the actual program edit was there was too much messing with the visuals. Catalyst doesn't compete with CSI Miami and doesn't need so many glassy visuals and fast edits, which only serve to make a hash of the explanations.
- 28 May 2009 10:58:46pm
In the event years where the water temperatures immediately north of Australia were cooler leading to the drier air mass & reduced rain, what was the intensity of the preceeding tropical wet. Could the volumes of water being discharged off the land mass have had any effect on the surrounding sea temperatures and thus the capacity to generate evaporation? Do wet years in the tropics = dry or wet years in the southern states and conversly dry years in the tropics = dry or wet years in southern states?
- 28 May 2009 9:21:14pm
I would be very hesitant to listen to much of what the Bureau of Meteorology has to say on the matter. It's only been the past three months that they have officially acknowledged the influence of the IOD on SE Australian rainfall - too preoccupied with ENSO. The Japanese Agency for Marine Earth Science (Jamstec) have considered IOD in Australian rainfall patterns for nearly a decade. Anyhow the BoM's latest ENSO update has the current IOD status the opposite way around! C'mon guys!
Anyway my own research strongly indicates we're headed for a negative IOD phase in the coming months, confirmed by the absence of a severe cyclonic event (Cat 4 or 5) in the Bay of Bengal in April and May. A wet spring awaits!!!
