NZ’s years-long warm spell
Several more warm years could be on the way, if a new statistical temperature forecasting system turns out to be accurate.
The system predicts it will be unusually warm from this year until 2022, even without including the impact of climate change.
The researchers from France, the United Kingdom and the Netherlands say they confirmed the accuracy of their system in a series of historical hindcasts from 1880 to 2016. In particular, a retrospective prediction using the system – called Procast – was able to capture the decade-long global warming hiatus after 1998.
The new system predicts global mean air and sea surface temperatures. A paper describing the research has been published in Nature, which said natural variability in the climate system was harder to predict than external forcing, such as greenhouse gas emissions.
‘‘A forecast for 2018, 2022 indicates that warming owing to natural variability will temporarily reinforce the long term global warming trend, leading to an increase in the likelihood of temperature extremes.’’
Niwa chief scientist, climate, atmosphere and hazards Dr Sam Dean said the article was suggesting extra warming should be expected on top of what would be expected from ongoing climate change.
‘‘Another way to think of this is that there is less chance of having fortuitously cool years thanks to natural processes.
‘‘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.
‘‘As an example, during the 2000s the world had more La Ninas, which led to cooler global temperatures, and the oceans took up lots of extra heat.
‘‘Since 2014 this appears to have changed, with more El Ninos and much hotter years,’’ Dean said.
As far as New Zealand was concerned, not every year that was warmer than usual globally was hot in this country.
‘‘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,’’ Dean 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.’’
The paper suggested the coming few years were likely to see extremes of heat and dryness 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.’’