The outlook? Continuing warm

Four seasons in a day is how many people describe New Zealand’s weather.

‘‘If you don’t like it now, just wait an hour,’’ is another popular saying, summing up the vagaries of the weather in the land of the long white cloud.

To the majority of us it is crystal clear the weather we experience now is quite different, generally much warmer, from how we recall it in years past — even accounting for rose-tinted spectacles.

While our average temperatures are rising at about the global rate, we have a relatively less extreme climate to begin with, which is quite variable with no big continental heating. That means extremes do not come through as strikingly quickly as can be seen somewhere like Australia.

Therefore, New Zealand’s mid-latitude and oceanic setting, which moderates the actual weather, is also shielding us a little from broader climate changes. And despite shifting atmospheric patterns, we do still have four seasons and it can feel like they all make an appearance on any one day.

However, as we have seen in the past two summers when previously rare marine heatwaves have significantly bumped up temperatures onshore too, even that maritime buffer cannot insulate us from a warming climate.

One of the great quirks of our changing climate is that, even when you think the weather is bucking the now well-recognised warming trend and things are getting cold, they aren’t really.

A chilly week or month now may still happen but is much more unusual, compared with how frequently cold periods used to occur and how long those spells would last. Today’s cold spells are often not as cold as they were just a few decades ago.

When we get extreme weather these days it seems much more likely to be on the warm end of the spectrum, in terms of heavy rain and high winds from tropical or subtropical airstreams, rather than heavy snowfalls from polar southerlies.

As one meteorologist put it recently, a warming climate does not mean it never gets cold. But it does mean it is becoming more difficult, and more unlikely, for anywhere in New Zealand to set cold temperature records. On the other hand, long-standing heat records are getting easier to break.

So what of 2019?

While there were some colder interludes from August to October, the overall theme was the same as the past five or six years — warmer than the National Institute of Water and Atmospheric Research’s 1981-2010 baseline average, derived from its seven-station series of temperature records taken since 1908 across several sites in Auckland, Masterton, Wellington, Hokitika, Nelson, Lincoln and Dunedin.

December, in fact, was the 35th consecutive month with average or above-average temperatures — the last with below-average temperatures being January 2017.

Niwa forecaster Nava Fedaeff told The New Zealand Herald the last time New Zealand had more than a single month of below-average temperatures was in 2012, which had six chilly months, making it the country’s ‘‘last properly cold year’’.

This run of 35 warmer months came close to being disrupted by the arrival of late winter for those in the South during September and October.

High above the South Pole, an exceptionally rare ‘‘sudden stratospheric warming’’ event was occurring as spring arrived, with temperatures about 30kmup nearly 70degC warmer than normal. Such heat at high altitude can unleash a chain reaction leading to more frequent bitter southerly outbreaks at the surface.

The last time this phenomenon happened with such intensity was in spring 2002, when New Zealand had its coldest October in 20 years. But this time, even such a potentially momentous chilling event only had a minimal impact on the warming trend.

Last October’s average temperature turned out just 0.3degC cooler than normal, a difference which statistically fails to even count as ‘‘below average’’, and is still technically within the bounds of ‘‘average’’.

And this year?

With 2019 likely to join 2013, 2016 and 2018 as one of New Zealand’s top five warmest years so far, it is hard to imagine 2020 changing tack.

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