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Scientist says climate mystery is solved -

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ELEANOR HALL: US scientists have identified a possible reason for the anomaly in recent temperature records which some climate change sceptics point to as evidence that global warming is being overstated.

The research has found that a natural cycle of cooling in parts of the Pacific Ocean has brought the temperature down, but the scientists predict that when this ends, warming will accelerate.

Simon Lauder has more

SIMON LAUDER: Planet Earth's ten warmest years on record have all occurred since 1998. But since 1998 the increase in global temperatures has not been as steep as scientists predicted, considering how much greenhouse gas levels have increased.

It's a point used by some scientists and sceptics to question the urgency of climate change warnings.

Now some scientists say they can explain this hiatus in global warming.

SHANG-PING XIE: You know the hiatus is going to be temporary. It's not going to make the man made warming go away.

SIMON LAUDER: In January climate scientist Professor Shang-Ping Xie was on a plane to Hobart when he read an article in the Australian newspaper which said that climate figures validate the sceptics.

Professor Xie says that was his inspiration.

SHANG-PING XIE: I read an article in the Australia newspaper highlighting this issue, so I thought, I need to do something about it (laughs).

SIMON LAUDER: Global temperatures are highly sensitive to the tropical Pacific Ocean, the home of the El Nino and La Nina weather systems. It's also the site of a much longer lasting cycle.

Professor Xie and his colleagues at the Scripps Institution of Oceanography in San Diego devised a new method for climate models to take equatorial Pacific Ocean temperatures into account.

He concludes that a cooling of the waters is counteracting the warming effect of greenhouse gases.

SHANG-PING XIE: The current cooling is only part of natural cycle of the Pacific Ocean.

SIMON LAUDER: And how do you then explain extreme weather events such as heatwaves in Europe and Russia and the melting of the Arctic Sea ice?

SHANG-PING XIE: Yeah, that's an excellent question because there is obvious contradiction, so we're looking into this seasonal variation in the climate occurred for the past 15 years. It turned out the pausing of the global warming occurred only during the northern hemisphere winter. In the northern hemisphere summer the tropical influence is weak, that's why even the annual mean global temperature shows no trend over the past 16 years. The northern hemisphere summer, global temperature has kept rising even over the past 15 years.

SIMON LAUDER: Professor Xie says if it weren't for the cooling trend along the equatorial Pacific, global warming would be much worse right now.

SHANG-PING XIE: This has been expressively demonstrated in our study.

SIMON LAUDER: So what do you think conditions would be like for the climate if it weren't for this cooling trend?

SHANG-PING XIE: Oh, it would be much warmer according to our calculation. Something like one, two degree Celsius warmer at this time. That's a significant number.

SIMON LAUDER: What will happen to the climate when this cool trend comes to an end, and you have any idea when that will be?

SHANG-PING XIE: Based upon model calculations, based upon analysis of past record, when the Pacific comes out of the cooler state, global warming is going to return and return at much accelerated rate. The warming rate is going to be as high as we saw during the period from 1970s to 1990s - that's a rapid warming period.

SIMON LAUDER: When do you think that will be?

SHANG-PING XIE: Oh that, unfortunately I cannot tell, because that's beyond the predictability of the current science.

SIMON LAUDER: What do you think climate change deniers will make of your study?

SHANG-PING XIE: Oh, I cannot predict. I think our study has narrowed their window (laughs). Whatever you say, they are going to say something they like (laughs).

SIMON LAUDER: The paper is published in the latest edition of the journal, Nature.

ELEANOR HALL: Simon Lauder with that report.