La Nina like weather events could become the norm if climate pattern shifts

A leading climatologist has found that a climate-change inspired shift in complex interlinking weather patterns may lead to Australia experiencing La Nina like conditions far more often.

While Australia's focus for leads on climate has long been the Pacific and Indian Oceans it is changes in the distant Atlantic that have attracted the interest of University of New South Wales climatologist Matthew England.

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Professor England said the Atlantic overturning circulation had a critical influence on weather patterns through the Americas and Europe.

This circulation sees a massive flow of warm tropical water up into the North Atlantic, which keeps Europe's climate mild despite its relatively northerly location, while a similar phenomenon happens in the southern Atlantic and around Antarctica as well.

However, Professor England said scientists had noticed a slowdown in this North Atlantic circulation over recent decades.

While this slowdown is happening a hemisphere away from Australia it has a potentially large impact on weather here.

Without the circulation taking warm water away heat builds up over the tropical Atlantic.

In turn this pushes dry air over the east Pacific, which strengthens trade winds and pushes warm water towards Australia and Indonesia, phenomena that are associated with a La Nina event.

"Should this trend continue in the Atlantic we'd expect to see a La Nina-like state in the Pacific Ocean far more often," Professor England said.

He said there was extensive concern about what such a change in climate would mean, but added Australia's agricultural heartland could be one of the few winners.

"It's very concerning for places like the south-west of the United States, where hotter and drier conditions would have a real impact on things like bush fire risk and food production systems and Australia's eastern seaboard, which would be at greater flooding risk."

"However, for inland parts of eastern Australia, such as the Murray Darling Basin, the higher rainfall would most likely be beneficial."

Professor England said the research highlighted the connections between the oceans.

"For years a lot of focus was on the individual oceans and their impact on climate, this shows how interconnected our climate systems are."

"It demonstrates that what is happening all the way over in the Atlantic can have a very real impact on what happens here in Australia."

The extent of the slowdown in the Atlantic circulation, or whether it shuts down entirely, is still yet to be assessed, but Professor England said even the changes already recorded would alter weather patterns.

"This is not a yes or no question, there are degrees of change, so the circulation slowdowns already observed is having an impact. What remains unclear is just how pronounced these changes will be."

He said should a pronounced slowdown or a shutdown occur in the Atlantic it would have an impact on climate for a significant amount of time.

"Once these events stop it could be centuries before they start up again."

He said climate records reaching back 120,000 years showed the Atlantic overturning circulation had switched off, or dramatically slowed, during ice ages.

It switches on and placates European climate during so-called "interglacial periods", when the Earth's climate is warmer.

Professor England said since modern human civilisation began around 5,000 years ago, the Atlantic overturning has been relatively stable, but added the current dynamic, with large scale emissions of greenhouse gases had never been experienced before.

He said only a large scale cutting of emissions would allow atmospheric conditions to return to more normal conditions, and stop events such as the Atlantic circulation slowdown.

READ MORE: Why the Atlantic overturning circulation is slowing down