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How the corals of the Great Barrier Reef affect Queensland’s climate -

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Robyn Williams: This week the marine scientists announced that 67% of corals off northern Queensland have been bleached and died, which raises the question about unexpected consequences. Corals, you see, affect weather. Did you know this? And the ship, the Investigator, sailed from Hobart up north to measure the effects. Here's Zoran Ristovski at the Queensland University of Technology.

Zoran Ristovski: Yes, the ship spent most of its time south, but this is the first time it's going into the Great Barrier Reef.

Robyn Williams: How far, how extensively?

Zoran Ristovski: We went up to Cairns on the inside part and on the outside part maybe up to Townsville.

Robyn Williams: And looking at a variety of corals or just one particular sort?

Zoran Ristovski: We were looking at the reef as a whole, the emissions from the whole reef.

Robyn Williams: How do you measure the emissions from a reef? Because surely they would mix with the water, how do you tell it apart from the general ocean?

Zoran Ristovski: Well, that's why we did the measurements on the outside part of the reef, but we also did measurements then on the inside part of the reef, and then we could see the difference. We also had a group of oceanographers and ocean modellers from CSIRO. They developed something called the eReef. So they have the whole reef, like a big model of the reef and the water flow, so we sit in a certain spot and they do the modelling for us and tell us exactly how and where the water flow is, where it comes from, and that helps us move the ship in the right position so we would get direct emissions from there. This is water, not air.

Robyn Williams: So the living corals, which also contain algae of course, give off something which is not there over an area of water where there is no coral beneath presumably. So what do they give off?

Zoran Ristovski: Well, not just that…DMS, dimethyl sulphate is the substance which is one of the driving substances of the climate, over the oceans mainly. It's something that algae in general emit. But coral is the only animal which also exudes, emits this substance, DMS. So both the algae living with the coral symbiotically, the zooxanthellae, and the coral itself emit DMS in water, that's why you get higher concentrations around corals.

Robyn Williams: And this is a sulphate, is it?

Zoran Ristovski: It's sulphate which goes from water, it then goes into the air. It's water-soluble gas. And once it enters the atmosphere it reacts with various oxidants under sunlight and forms sulphuric acid which then forms tiny particles which can seed clouds.

Robyn Williams: It seeds the clouds which then rain on you, do they?

Zoran Ristovski: Or not.

Robyn Williams: Yes, well, you've got it both ways then, haven't you.

Zoran Ristovski: Yes, the effect can go both ways. So if you have too many of these seeds, what will happen is that your cloud droplets will become smaller and they won't rain, and eventually they will evaporate. So it can go in both directions. If there's no seeds then these seeds are necessary to form the clouds. If there's too many of them the clouds become white and they don't rain.

Robyn Williams: So you've taken zillions of measurements, and presumably, having just left the ship, you've not come to a conclusion yet about whether it's yes or no. How long will it take you?

Zoran Ristovski: Realistically at least a year, and then I would give it realistically another year to synthesise it into a good story.

Robyn Williams: Can't you just take a picture of the clouds above the reef and say, hey, they're different, boing?

Zoran Ristovski: No, you can't. It's really complex. You see the cloud but what we were looking at is where did the seeds that form that cloud come from. So was there like a lift from the ocean upwards and then the cloud was formed, or did the air come somewhere from further away, so those of all the things that we are looking at, and we have to know.

Robyn Williams: What if the reef does have that effect on clouds and the weather, what's the implication?

Zoran Ristovski: Well, the implication would be that the reef will change. I won't say die, it's a hard word. Because the sea surface temperature is going up and we can't stop that. So with the increase of the sea surface temperature, the current species of coral living there will most likely die off. Will some new coral species take over? I don't know, I'm not a coral person, but that's one of the theories I heard.

So what we are looking at is if the coral and the reef dies off or when the coral, I would say, when the reef dies off or changes, not if but when, what consequence will that have on the cloud formation above Queensland, particularly the north part of Queensland? And what consequence will that have on the rainfall pattern? Will it become drier or wetter?

Robyn Williams: I know it may be a different sort of sulphate, but of course people talk about sulphates being in the atmosphere, coming from volcanoes, even with geo-engineering seeding the sky with sulphate. Is this the same animal?

Zoran Ristovski: Yes, it's the same sulphate in the end, it's the sulphuric acid which comes from volcanoes as well and forms these sulphate particles, so exactly the same thing, yes.

Robyn Williams: So when you find that there is a difference, if there is a difference according to the coral, that really on the face of things will be rather troubling, because if you've got this enormous living thing that's affecting the weather and it's dying, the weather will change somehow.

Zoran Ristovski: 70% of the world is covered by oceans, and most of the clouds are actually formed over the oceans. So another thing which we hope that maybe some of our work could infer a more broader picture into what would happen with the increase of the temperature of the ocean, changing the species et cetera, changing that DMS flux.

Robyn Williams: I remember hearing from the people who talk about the Gaia hypothesis, about the…it's all part of the same thing?

Zoran Ristovski: Yes, it's part of that same thing. The Gaia hypothesis, it actually comes from James Lovelock who was one of the founders of that idea, and he was the person who found the link between DMS and cloud seeding and cloud formation. And it goes along that algae emit this DMS substance when they are under stress and exposed to higher temperatures or increased UV radiation. And that DMS oxidises in the air and forms a cloud above the algae, so it will cool it down. We didn't manage to prove it. It sounds interesting and good, but I think 20 years after the hypothesis, and I don't know how many cruises, attempts, we still didn't prove the hypothesis.

Robyn Williams: Well, that's how science works, isn't it, you go out and you get the information and you crunch the numbers, and you've got zillions of numbers, haven't you.

Zoran Ristovski: Oh yes, we've got a lot of…gigabytes of data. So I think now it's going to be a big task of getting enough manpower to go through the data.

Robyn Williams: Congratulations.

Zoran Ristovski: Thank you.

Robyn Williams: Professor Zoran Ristovski from the Queensland University of Technology.


Guests
Zoran RistovskiProfessor of Atmospheric Science, Environmental Engineering, Environmental Science and Management
Queensland University of Technology
Brisbane QLD

Further Information
Zoran Ristovski at QUTDoes coral create rain? - ABC News

Credits
PresenterRobyn Williams ProducerDavid Fisher