If you thought 2018 was rather warm, then you were right - it was New Zealand's second warmest year on record.

It is part of an overall warming trend, which a leading climate scientist says is a "wake-up call" for politicians to take action.

In its annual summary released today, Niwa said 2018's mean of 13.41C was 0.8C above its records since 1909, equalling 1998.

It fell only to our most scorching year on record in 2016, 0.84C above average.

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Last year also marked a new record for the warmest minimum temperatures, previously held by 2016.

Niwa principal scientist Chris Brandolino said 2018 was part of a larger warming trend, with four of our past six years in the top five hottest years on record.

Key stats included:

• 2018 was the second equal hottest year on record, 0.8C above average, equalling 1998 but behind 2016.

• January was New Zealand's warmest month - ever, at 3.1C above average.

• Three ex-tropical cyclones struck New Zealand in 2018: Fehi, Gita and Hola.

• The hottest recorded temperature was 38.7C in Alexandra on January 30. The coldest was -10.4C at Mt Cook on June 3.

• The wettest part of the country was Milford Sound, recording 6818mm. The driest was Clyde with 526mm of rain.

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Brandolino said January was the warmest month of any year on record, at 3.1C above average.

Many parts of the country recorded their warmest year on record, including, Kerikeri, Te Kuiti, Hastings, Levin, Wellington at Kelburn and Southwest Cape.

Brandolino said there were three main drivers of the warm temperatures.

The first was ocean temperatures, with New Zealand experiencing a "marine heat wave" in the first few months of the year. Some parts of the sea recorded temperatures 2C above average.

"New Zealand is an island nation, so where ocean temperatures go, they also go on land."

New Zealand also experienced more subtropical airflow in 2018, with many lows to the west and highs to the east driving northeast winds.

The increase in greenhouse gases, surpassing 400 parts per million, was the third factor, providing a "long-term tailwind to temperatures".

Wake-up call for action on climate change

Climate scientist Dr Jim Salinger had predicted last week 2018 would be our hottest year on record, but was happy with Niwa's conclusion.

"We used slightly different calculations, but we are all consistent in that we are in the hottest period on record."

Niwa also found 2018 had the hottest minimum, or overnight, temperatures on record.

Salinger said this was a "wake-up call" for politicians to take action on climate change.

"It is very concerning, and politicians are not yet doing anything about it.

"We recognised this was happening back in 1980, now it is starting to almost get too late.

"The young are calling for it, so let's get the Zero Carbon Bill in and with bipartisan support. The evidence is out there.

"As we see further temperature rises we are going to see a lot of extinctions, people living around the coasts and in small island states will be affected by rising seas, and our oceans will become more acidic."

Dr Huw Horgan of Victoria University looks out at the Fox Glacier. Since the 1970s it has fluctuated, but between 2009 and 2018 it has made a dramatic retreat. Photo / Dave Allen, Niwa
Dr Huw Horgan of Victoria University looks out at the Fox Glacier. Since the 1970s it has fluctuated, but between 2009 and 2018 it has made a dramatic retreat. Photo / Dave Allen, Niwa

Already in New Zealand we were experiencing dramatic impacts, particularly in the Southern Alps.

Last summer's "unprecedented" heatwave and covered an area the size of the Indian subcontinent - 4 million square kilometres. It lead to the largest annual ice melt from our Southern Alps glaciers when 3.8 cubic kilometres, or nine per cent of permanent snow, went down our rivers.

This brought the total down to 37.5 cubic kilometres, compared with 60 cubic kilometres in 1962, a 38 per cent reduction.

Last summer's heat saw very early Sauvignon Blanc wine-grape maturation in Marlborough, and major species disruption occurred in our marine ecosystems with snapper were caught in Fiordland.

Salinger said it mimicked global trends, where surface temperatures over the past four years have also been the warmest on record.

Niwa's seasonal climate outlook forecasts the next three months being above average too.

Salinger said this was consistent with predictions from the United Kingdom Met Office 2019 would be close to a record due to global heating and the added effect of the El Niño in the tropical Pacific.

"The Met Office forecasts the global average temperature for 2019 to be between 0.98C and 1.22C, with a central estimate of 1.10C, above the pre-industrial average period from 1850–1900.

"Since 1850, 2016 is the warmest year on record with a central estimate of 1.15C above the same baseline."

Like an endangered species, many of New Zealand's glaciers are no longer easily accessible and several are on track to disappear completely in the coming years. Photo / Dave Allen, Niwa
Like an endangered species, many of New Zealand's glaciers are no longer easily accessible and several are on track to disappear completely in the coming years. Photo / Dave Allen, Niwa

Along with the heat there were also several extreme weather events in 2018.

In a typical year one ex-tropical cyclone would come within 150km of New Zealand. In 2018, three ex-tropical cyclones impacted New Zealand in Fehi, Gita and Hola.

Gita, which struck over February 20-21, brought significant rainfall, leading to slips and road washouts.

In southeast Kaikōura there was 202mm in 30 hours, nearly four times the monthly normal and 28 per cent of its annual rainfall.

The major event for Auckland occurred over April 10-11, with extreme winds causing major power outages across the region. The strongest gust in the city was 146km/h at the Sky Tower.

MetService meteorologist Lisa Murray said it was a "very busy" year for them, issuing many severe weather warnings.

"It was the wettest February on record for Nelson and Blenheim (records at both locations started in 1941). The rainfall was nearly four times the usual February amount.

"The wind storm in Auckland on 10 April cut power to a record number of households, the largest power cut in New Zealand's history.

"Thunderstorm activity was widespread across the country for the final month of the year, recording 119,698 strikes in December over New Zealand and coastal waters. December 14 saw 33,218 lightning strikes in just 24 hours."