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El Nino will get worse under climate change – BoM

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Larissa Waters 26 May 2015

Senator WATERS: Thank you, Chair. Thanks Dr Vertessy and Ms Middleton for coming today. Sticking with El Nino, can you explain the impact of El Nino on global temperatures?

Dr Vertessy: Yes. I think this infographic might even say it: a large number of the big jumps in global temperature are associated with El Ninos. This is because El Nino is the largest climate influence on the whole global climate system. What it is really all about is the turning over of heat energy from the oceans to the atmosphere. So during a La Nina—the opposite—we see a dominance of heat being subducted down into the deep ocean from the atmosphere. We have been in a kind of La Nina dominated phase, you might say, since 1998, which was the last big El Nino where there was a temperature spike. The risk now is, if this El Nino continues to intensify, there is a good chance that we will see global atmospheric temperatures start climbing much faster again, as they did prior to the last El Nino.

Senator WATERS: Another senator asked you about the impact of climate change on El Nino. You said there was a mooted relationship. My understanding from CSIRO is that, they say, climate change will double the risk of super El Nino—the really extreme ones—to one every 10 years. Do you share that view?

Dr Vertessy: That is based on outputs from model projections. They are not observations, which is the difference I would draw. It is not to say they are invalid at all, but that is why I am saying they are mooted. We have not observed such changes per se. But they are projected to occur on the basis of what the models are telling us.

Senator WATERS: Your models are also telling you that same information?

Dr Vertessy: Yes. We are operating with the same model base. Everything that CSIRO is talking about is effectively something that we are doing in collaboration with them with a joint model.

Senator WATERS: It is modelled that super El Ninos will become twice as frequent; namely once every 10 years, as climate change intensifies.

Dr Vertessy: We don't use the term 'super El Ninos'. We would say that strong El Ninos are likely to be more frequent. I cannot remember the exact figure of frequency increase, but I do know that they are increasing.

Senator WATERS: Perhaps you could take it on notice. My understanding is that it is one every 10 years, which is a doubling.

Dr Vertessy: We would be happy to provide a more detailed answer to that.

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