Temperatures across the globe are likely to be unusually warm over coming years, with greater chance of extremes, scientists have predicted.
A cutting-edge new statistical model, detailed in a study published today, found there was a 72 per cent chance of higher-than-normal global temperatures between now and 2021 - and a 69 per cent likelihood of warmer sea surface temperatures.
While it wasn't clear whether New Zealand would experience the same heat, scientists say temperatures here were likely to be higher when global ones were too, as happened in record-hot 2016.
The UK and Dutch scientists who developed the model found the climate wouldn't just be warmer as a result of increasing temperatures from climate change, but the extra heat they put down to natural variability in the climate system.
By being able to capture that natural variability in their model, they could predict the long-term global warming trend would be "temporarily reinforced" by the hotter stretch likely to come.
Dr Sam Dean, Niwa's chief scientist for climate, atmosphere and hazard, said predictions like that of the model were "usually a bit better than guessing", as variability in climate-driving ocean circulation could change slowly over many years.
"As an example, during the 2000s the world had more La Niñas, which led to cooler global temperatures, and the oceans took up lots of extra heat," he said.
"Since 2014 this appears to have changed, with more El Niños and much hotter years."
The new model, along with work by forecast centres such as the UK Met Office, were predicting that these particularly hot years could continue as a result of this natural variability in the oceans.
"While we can't be sure exactly how things will play out, at the moment the odds are higher for hot years."
Dean said that didn't mean New Zealand would get the same, as not every hot year globally was also hot here.
"This is because whether we get hot weather or cold is also dependent on whether our wind blows more from the north or the south, and this is a very local effect," he said.
"But it is also true that all things being equal the odds of a hot year here are higher when global mean temperatures are higher.
"For example, 2016 was the hottest year globally since records began, and it was also the hottest year recorded here in the Niwa national temperature series."
Victoria University climate scientist Professor James Renwick said it would be interesting to see if the new model performed well into the future.
If so, such forecasts would be invaluable for sectors ranging from agriculture and energy to emergency management and public health.
"As the climate warms, getting extra-warm years will translate to a much greater occurrence of extreme heat, dryness, and a greater chance of wild fires, as we are seeing in the Northern Hemisphere summer this year," he said.
"This paper suggests that the coming few years are likely to see such extremes continue."
And if the warming trend caused by greenhouse gas emissions continued, Renwick said, years like 2018 would be the norm in the 2040s - and would be classed as cold by the end of the century.
Already, the planet's 10 warmest years since 1880 had all fallen within the last two decades.
The new study comes as climate scientists are predicting a 78 per cent chance of El Niño conditions over New Zealand between February and April, although early indications suggested it wouldn't be a strong event.