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Climate study adds more heat to global warmin -

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MARK COLVIN: German scientists say they've identified a previously overlooked factor in climate change.

In a study published today, they say one effect of global warming is that the oceans will release less of a gas which helps shield the Earth from the sun's radiation.

That means the oceans themselves will act as a significant contributor to climate change.

An Australian expert says it's a very significant study, and she agrees with the authors that it should be factored into future climate change projections.

Simon Lauder reports.

SIMON LAUDER: As the oceans absorb carbon dioxide they become more acidic, hindering the growth of phytoplankton, which produce a sulphur compound called dimethyl sulphide, or DMS. So the more acidic the oceans, the less DMS the oceans emit into the atmosphere.

Dr Katherina Six says that's bad news for our climate.

KATHERINA SIX: It actually scatters back sunlight coming in onto the Earth, and it actually regulates our climate in the fact that more DMS means more cooling for the Earth.

SIMON LAUDER: Dr Six and her colleagues at the Max-Planck Institute for Meteorology have used simulations to determine the effect ocean acidification has on the production of sulphur.

She estimates this effect could add to global warming by between 0.23 and 0.48 of a degree by the end of this century.

KATHERINA SIX: The reaction from the DMS emission was about 18 per cent in 2100 compared to pre-industrial times. And this gives us a temperature response of about 0.23 to 0.4 Kelvin or Celsius as an additional warming at the end of this century.

SIMON LAUDER: In other words we can add another half a degree to estimates of global warming because of what you've found.


SIMON LAUDER: Dr Six says this mechanism is not included in current projections of future climate change, and her team is the first to highlight the potential climate impact due to changes in the global sulphur cycle triggered by ocean acidification.

KATHERINA SIX: Nobody actually looked at the natural background concentration, and this is absolutely new that we found a mechanism that could change the natural background concentration.

SIMON LAUDER: Dr Robyn Schofield, from the Melbourne University School of Earth Sciences, says this is a very significant study.

ROBYN SCHOFIELD: That's a global estimate. I'd say what's probably more worrying, and perhaps more of a climate issue, is that it's really quite regionally different because it's positive at the 40 degree level and negative in the polar regions. So sulphur, depending on where you emit it, has quite a different role. It's unlike carbon dioxide, where it's just globally increasing the temperature.

SIMON LAUDER: It really is a bit of a wildcard by the sounds of it.

ROBYN SCHOFIELD: Clouds are a wildcard, and this is really playing with clouds.

SIMON LAUDER: And what do you think of them saying that this should be included in climate change projections in the future?

ROBYN SCHOFIELD: It should be. It's really capturing the complexity of the climate system, and we're only now getting the capability to look at these issues.

SIMON LAUDER: The chief executive of the Climate Institute, John Connor, says he's concerned by the discovery of a new positive feedback loop for climate change.

JOHN CONNOR: Well what we've seen is already about 0.8 of a degree warming above pre-industrial levels, and already we're seeing a significant increase in extreme weather events and climate impacts. This adds to the tipping point, and so it would be a great concern. We need things which actually help reduce that warming and not add to it.

SIMON LAUDER: Details of the study appear in the latest edition of the journal Nature Climate Change.

MARK COLVIN: Simon Lauder.