Next five years predicted to be abnormally warm

The next five years will be abnormally warm, according to a new forecast system.

UK and Dutch researchers developed the 'probabilistic' statistical model that can make predictions of global mean surface air temperature almost instantly on a laptop. A report on the system was published in the journal Nature Communications.

It's predicted 2018 to 2022 will be an "anomalously warm period" and extreme temperatures will be more likely. These changes are due to both greenhouse gas emissions and natural variability.

On top of higher temperatures caused by climate change, the forecast suggests the world can expect 'extra warming' in the next few years because of natural variability.

"Another way to think of this is that there is less chance of having fortuitously cool years thanks to natural processes," says Dr Sam Dean, NIWA Chief Scientist of Climate, Atmosphere and Hazards.

"We can't be sure of course but we do know that predictions like this are usually a bit better than guessing, because of variability in ocean circulation that can change slowly over many years."

He says an example is the abundance of the La Niña climate pattern phenomenon during the 2000s, leading to cooler global temperatures while the oceans absorbed extra heat. The climate pattern has changed since about 2014, when El Niños became more common resulting in much hotter years.

"This article, as well as work by forecast centres such as the UK Met Office, are predicting that these particularly hot years could carry on for a while now as part 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."

In terms of what the prediction means for New Zealand, Dr Dean says global temperature averages aren't always reflected in the South Pacific.

"Not every hot year globally is a hot year in New Zealand. 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.

"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."

Professor James Renwick from the School of Geography, Environment and Earth Sciences at Victoria University says the new 'decadal' forecast system (which predicts climate in the coming two to 20 years) is at the forefront of climate prediction research.

"If such forecasts could be made reliably they would clearly be of great value in many sectors: agriculture, energy, emergency management, public health, etc. Most research is focused on using dynamical global climate models (GCMs, as used for climate change simulations), where the ocean state is very carefully specified for the present day."

He says researchers have used a clever statistical approach which performs well on recent past fluctuations in global temperatures, and statistical models are appealing because they can be run quickly on personal devices such as laptops or cell phones unlike GCM simulations which can take weeks and need specialised technology.

"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 says.

"This paper suggests that the coming few years are likely to see such extremes continue.

"If the warming trend caused by greenhouse gas emissions continues, years like 2018 will be the norm in the 2040s, and would be classed as cold by the end of the century."