Climate cycles that could mean we're about to get even hotter

El Nino, and its sister La Nina, have long been one of the key drivers of Australia's weather.

But environmental scientists now suspect they could be little more than the climactic equivalents of cheeky kids at the family barbecue. Instead, a "kindly aunty" and "cranky uncle" could have a far more wide reaching effect on our climate.

With El Nino being the Spanish for "the boy" and La Nina "the girl" scientists have named these overarching systems El Tio meaning, "the uncle," and La Tia "the aunt".

And if the boy and the uncle join forces, things may be about to get hairy. At the very least, you may want to slap on some more sunscreen, reports News.com.au.

Dr Benjamin Henly, a climate scientist at the University of Melbourne, told news.com.au a prolonged La Tia may have "lulled us into a false sense of security" that global warming had slowed when the reality is climate change could be on the verge of accelerating.

That could spell disaster for the 2015 Paris Climate Agreement which aimed to keep the world's average annual temperatures to 1.5C below pre industrial levels.

The El Nino Southern Oscillation (ENSO) is a climate cycle operating in the Pacific.
A negative ENSO phase, commonly known as an El Nino, sends hotter weather to Australia and can lead to less rain, sustained droughts and weather extremes. A positive ENSO, La Nina, sees cooler conditions and more rain.

Seven out of the 10 driest Australian summers have coincided with El Nino, including 2016 which was the hottest year on record.

One of the big differences between the kids at the climate barbecue and the elderly relatives is the length of time they last.

El Ninos and La Ninas tend to exhaust themselves and collapse in a heap every three to five years. But El Tio and La Tia have more stamina and keep going far longer.

"El Tio, the cranky uncle, is responsible for increasing global temperatures in decade to decade cycles while the negative phase, La Tia the kind aunty, is responsible for slow down periods,"said Dr Healey.

When in full swing, El Tio can exacerbate the effects of an El Nino and a La Nina while La Tia can reduce them.

The scientific name for El Tio and La Tia is the tongue twister Interdecadal Pacific Oscillation (IPO). It's been known about for some time but it's only in recent years it's been thought to have such a strong effect on the ENSO.

In the journal Geophysical Research Letters, Melbourne University researchers said they feared that a prolonged kindly aunty has lessened the extremes of the previous decade's El Nino masking the real effects of global warming.

"We've been in the cool (La Tia) phase since 2000 and that may lulled us into a false sense of security," said Dr Healy.

Indeed, a chart produced by the researchers shows that between around 2000 and 2010, global temperatures increased at a slower rate than the previous decade.

An El Nino sees warmer water in the eastern Pacific and hot, drier, conditions in Australia. Photo / News Corp Australia

This seeming slow down on global warming has been the thorn in the side of climate scientists leading climate change deniers to say its proof the worst predictions aren't coming true.

"We thought it wasn't warming so quickly, but if this mechanism turns around into a positive El Tio phase that could actually accelerate global warming," said Dr Healey.

"Many sceptics will say climate change isn't happening but what you see is this long term change happening due to human impact and natural variability."

As for keeping temperatures below 1.5C, the Melbourne researchers don't hold out much hope.

Already US President Donald Trump has said he will reconsider America's commitment to the Paris Agreement as part of his war on what he terms "job-killing regulations".

Sticking to a "business as usual" approach to emissions - basically pumping as much carbon into the atmosphere as we are currently doing - the team modelled when the world would breach 1.5C.

Under La Tia, it could take until the mid-2030s to top out on the temperature rise. But if the cranky uncle kicks in, the world could pass 1.5C as early as 2024.

"It doesn't mean the Paris Agreement is a waste of time but stabilising below 1.5C will mean massive global co-operation," Dr Healey said.

At the moment, we're in a neutral ENSO meaning the Pacific is essentially dancing on the precipice of either El Nino or La Nina.

But should we fall into a negative ENSO coupled with an El Tio it could lead to a supercharged El Nino, the paper argues.

"The effect of global warming at higher temperatures are more extreme and the things to expect are heatwaves, extremes in climate and more coral bleaching. And already the bleaching has been massive; it's like the climate change canary in the coalmine."

The climate kindly aunty may have made us complacent, Dr Healey said. If El Tio kicks in, only by dialling down on the human effects of global warming will we lessen its impacts.

"In terms of climate change, it's like steps up a mountain. There's valleys and peaks but we're still going up."