A Kiwi climate scientist says he's been alarmed at how much sea ice the planet's poles lost in 2016, in what was one of the hottest years on record.

Dr James Renwick of Victoria University has been tracking levels of sea ice in the Arctic and Antarctica, where, as 2017 dawned, more than one million square kilometres of ice was missing when compared with the historical average.

Renwick said sea ice extent had been more than two million square kilometres below normal every day since September 1, according to the Sea Ice Index published by the US-based National Snow and Ice Data Centre.

Over a 76-day stretch between October 13 and December 27, more than three million square kilometres of ice were missing.


Although overall ice extent had been below average at both poles, the picture in the Arctic has been much clearer and more dramatic over time.

There, the rate of loss was much more rapid - it now had 40 per cent less ice in late summer than it did in the 1980s.

Meanwhile, Antarctica overall saw around 4 per cent more sea ice in winter, up to 2014.

In the past two years, however, sea ice has been in decline around the frozen continent, with the extent falling to record lows in the last few months of the year.

In the Northern Hemisphere, the sea extent had been close to record low levels on most days in 2016, and, as winter advanced, ice extent decreased three separate times at a time ice should have been growing.

"So, after the sun went down and the Arctic ocean became dark and cold, even then, sea ice managed to melt, which is pretty remarkable."

Renwick expected the impacts of a strong El Nino in the first six months of the year, together with the background effects of polar amplification, had made 2016 an exceptionally warm year for the region.

"We've seen these temperature spikes there, where it's been 20C above normal over the North Pole, and temperatures being above freezing over the pole on Christmas Day."

What had been observed over the year had surprised even climate scientists.

"The bottom line is that our knowledge of what's going on in the Arctic must be a little bit behind reality, because the ice loss and the loss of seasonal snow has been faster than expected as well."

"While I'd be surprised if 2017 was as extremely warm for the Arctic, there's no getting around the fact that things are warming up very quickly there - and it's going to be another low year for sea ice."

Around Antarctica, where all sea ice melts away then grows back each year, levels had been running close to average until early September.

Since then, the extent had been well below normal every month, something which could partly be explained by a change in atmospheric circulation.

This had enabled warmer air to penetrate higher latitudes more effectively than was normally seen in spring, melting the ice.

"No doubt there were more things going on than that, but one thing we've learned over the last few years is that what the winds do over the Southern Ocean have a very large role in how the sea ice varies."

However, if the planet continued to warm at the rate it was, heating up ocean water and hindering sea ice growth, ice levels at both poles would ultimately reach the same end point.

The fresh observations come as scientists are poised to announce what temperature records 2016 broke.

The National Institute of Water and Atmosphere is scheduled to make an announcement early next week after last month indicating that 2016 would be New Zealand's hottest year on record, breaking the previous record set in 1998.

The year also saw the amount of carbon dioxide in New Zealand's atmosphere rise for the first time over the symbolic threshold of 400 parts per million. The level - reached for the first time in Hawaii three years ago - was also reached at the South Pole in June.

New Zealand and climate change

• Under present projections, the sea level around New Zealand is expected to rise between 50cm and 100cm this century, while temperatures could also increase by several degrees by 2100.

• Climate change would bring more floods (about two-thirds of Kiwis live in areas prone to flooding); make our freshwater problems worse and put more pressure on rivers and lakes; acidify our oceans; put even more species at risk and bring problems from the rest of the world.

• Climate change is also expected to result in more large storms compounding the effects of sea level rise.

• New Zealand, which this year reported a 23 per cent increase in greenhouse gas emissions between 1990 and 2014 - has pledged to slash its greenhouse gas emissions by 30 per cent from 2005 levels and 11 per cent from 1990 levels by 2030.