A new study led New Zealand's top climate scientists has explored last year's record-hot summer – and why it's relevant to our future under climate change. Its lead author, Professor Jim Salinger, answered these five key questions.
Your new paper reviewed the record-hot summer of 2017-18 and the extraordinary mix of factors involved. These notably included a persistently positive Southern Annular Mode which brought fewer cold fronts, a La Nina climate system, and background global warming. What aspects of it were most striking to you as a scientist?
The most amazing aspect to me was the size, how long it lasted and intensity of it.
The heatwave covered a huge area equivalent to the size of the Indian subcontinent – 4 million square kilometres and included all the south and central Tasman Sea, the land mass of New Zealand, and east in the Pacific to the Chatham Islands.
Heatwave conditions lasted 147 days, and sea surface temperatures peaked at 3.7C [above average] and land air temperatures at 3.2C for January.
The latter was the warmest month in 150 years of climate observations.
Will it likely be some time before we see a similar set-up of such a wide range of climate drivers?
As a guide, the last time a similar New Zealand heatwave occurred was in the summer of 1934/35 - more than 80 years ago.
That summer was described at the time as "remarkably warm" by the then director of the New Zealand Meteorological Service, Dr Kidson, with a mean temperature of 18.5C - 1.9C above the current 1981-2010 average.
The accompanying marine heatwave covered a slightly smaller area.
Sea surface temperatures were 1ºC above average for the entire season surrounding New Zealand, and 2C off the west coast of the South Island.
So in the current climate it might be a one-in-80-year event.
You've said last summer – and some of the heat we've had over the past month – could serve as a good analogue of what we might get at the back-end of this century. Can you elaborate on this?
Yes - looking to the future, we can compare the conditions experienced in 2017/18 with what climate models predict for the future.
The extreme warmth of last summer would be typical summer conditions by 2100, if we keep emitting greenhouse gases giving a warming of a couple of degrees above pre-industrial temperatures.
If emissions keep increasing as they have done recently, last summer will seem cool by the end of the century.
Against a warming trend, six of our warmest years have fallen within the past two decades. With new records now becoming something of a norm, do you think people are waking up to climate change?
The statistics are revealing it.
For example, in 2008, surveys showed only a third of farmers in Australia accepted the science of climate change, trailing behind the general population whom have consistently accepted the science.
By 2016 this had increased to 43 per cent.
By 2018 most Australians - 76 per cent – now accept the reality of climate change.
Although surveys have not been done in New Zealand, the Australian results would likely reflect New Zealand and agree with worldwide trends.
If there's any take-home from your study: what do you hope that is?
The impacts from such heatwaves are dire – for example last summer's warm conditions caused massive ice loss in South Island glaciers.
The Marlborough grape harvest was unusually early in 2018, two to three weeks ahead of normal.
Life in the oceans around us were significantly disrupted: coastal seaweed forests struggled to grow, farmed salmon in the Marlborough Sounds died and Queensland groper occurred in Northland – 3000km out of range.
This is yet another dire warning that we must hasten our action on reducing emissions as time is running out.