“If an El Nino does develop, it does look like we could see those [current dry] conditions extending through spring and into summer," Robyn Duell, acting manager of the bureau's long-range forecasting service, said. "It’s really not good news."

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With all of NSW declared in drought, the focus of agricultural concern is shifting to northern Victoria and south-eastern South Australia. These areas had been faring better after late autumn rains but precipitation since had been poor.

“A lot of people in northern Victoria are worried because they really need to have a good spring in this situation, and the outlook is not good for north of the divide," Ms Duell said.

An El Nino would likely nudge temperatures in Australia' - and globally - as weaker easterly equatorial winds reduce the amount of heat absorbed by the Pacific.

This year is already on track to be among the five hottest years since standard records began more than 120 years ago, agencies such as NASA predict.

New research published in Nature Communications forecasts those annual records could be challenged in coming years with an unusually warm spell predicted globally for the 2018-2022 period.

The work, published by European researchers Florian Sevellec and Sybren Drijfhout, used a statistic model that captured global mean and sea surface readings from 1880 to 2016 to develop a projection longer than most forecasts.

Natural variability had contributed to a slowing of surface temperature increases for a period after 1998 even as the overall biosphere continued to trap more heat from rising greenhouse gas levels. That variability will now "temporarily reinforce the long-term warming trend", the paper said.

"The coming warm period is associated with an increased likelihood of intense to extreme temperatures," it said.

The added temperature increase is in the order of 0.05 degrees, which compares to the typical 0.1-0.2 degree boost to global temperatures during an El Nino event.  The probability of extreme warm events for sea-surface temperatures will rise by as much as 400 per cent, the paper said.

"The statistical method in this paper appears to be a useful contribution to a key challenge faced by climate science, that is, improved interannual to decadal predictions of the internal variability in the climate," Ben Henley, a climate researcher at Melbourne University, said.

That includes "the year to year, and decade to decade variability around the externally forced response - primarily from human activity".

Still, Dr Henley said caution was needed in part because of limited information in the paper: "I would need to have a more detailed description of the method and a sample of the code before I could endorse this approach".