New Zealand's destiny is inextricably tied to that of its celebrated environment. But our blue and green backyard is now under unprecedented pressure from a wave of pests and human activity, ranging from development and pollution to climate change and tourism. In the second part of our week-long series, 50 Questions About the Environment, Victoria University climate scientist Professor James Renwick discusses the threats we face from a warming planet.

Guidance tells us we can expect several degrees of warming this century and between 30cm and a metre of sea level rise. What are the best and worst case scenarios and what will determine whether these play out?

The best-case scenario is that we have only another 0.5C of warming and another 50cm of sea level rise, through this century and into the next.

This much more change would still mean big disruptions for coastal communities everywhere and a greater risk of problems for global food supplies.

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This scenario would require global emissions of greenhouse gases (GHG) to peak in the next year or two and for emissions to get to zero globally around 2050.

The worst-case scenario is that we have 4C of warming this century, with nearly as much again over the following century.

That would be accompanied by perhaps 1.5m of sea level rise this century, and about 70m more over the following 1000 years.

That much warming would melt all the ice on the planet.

Such a future would mean massive disruption to societies everywhere, billions of people displaced, and possibly billions of deaths through famine and war.

The end of civilisation as we know it, in other words.

To achieve this, we keep growing GHG emissions, or at least not reducing them, for the rest of this century and beyond, until all the viable fossil fuel reserves are burnt.

What do you feel are New Zealand's greatest vulnerabilities from the impacts of climate change?

That's an interesting question, and I am not sure I know the answer.

My suspicion is that we are economically vulnerable to what happens elsewhere.

We are very connected internationally and if international trade is disrupted that would be hard for New Zealand.

READ MORE: Is our media covering climate change well?

Also, I think we'll be a magnet for climate refugees or migrants and we'll strain to deal with the numbers of people who may want to come here.

Climate Change Minister James Shaw has announced a zero carbon goal by 2050 and the establishment of an independent Climate Commission. Photo / File
Climate Change Minister James Shaw has announced a zero carbon goal by 2050 and the establishment of an independent Climate Commission. Photo / File

Domestically, the effects of sea level rise will be a growing issue, and the costs of adapting could be large, with more frequent floods, and droughts that damage agricultural production.

Gross greenhouse gas emissions have climbed by around 25 per cent since 1990. When you look at net greenhouse gas emissions, the increase has been around 64 per cent.

What has driven this and does it tell us New Zealand has been poor at addressing climate change?

The difference between gross and net is explained by cutting down trees, basically.
Our "sinks" of CO2 have decreased as forests have shrunk.

Our sources have grown mostly from transport and industry.

We have one of the highest car-ownership rates in the world and use a lot of fossil fuel to power industrial plant.

Both net and gross numbers tell us that New Zealand has done nothing to address the causes of climate change.

READ MORE: Major climate report: the five defining figures

In fact, recent governments appear to have been content to live with the knowledge that we are doing more over time to change the climate.

The pledge New Zealand made as part of the Paris Agreement - to slash emissions to 11 per cent below 1990 levels and 30 per cent below 2005 levels have been criticised by climate advocates as lacking, but considered fair and ambitious by the previous government. Your colleague at Victoria University, Professor Dave Frame, has also argued the commitments are at the strong end of the international spectrum. What is your own view? Are we being bold enough?

I do not think New Zealand is being bold enough.

We have abundant natural resources in terms of wind, water, and sunshine and should be able to power our economy entirely from renewable sources within 20 to 30 years.

Being a leader in this area will have benefits for our economy, while dragging the chain is bound to cost us in comparison to those who do lead.

There are well-known steps that could be taken to reduce our emissions by around 40 per cent compared to 1990 within the next 15 years.

But whatever the targets, my main problem with current policy is that most of the "reductions" come from buying credits internationally - or paying others to reduce emissions while we increase ours.

Obviously, not all countries can do this as someone somewhere has to be actually reducing their emissions.

This approach goes against the ethos of the Paris Agreement, which calls on developed countries to lead the way with actual reductions in emissions.

The new Government has committed to implementing a Zero Carbon Act and an independent Climate Commission. Does this give you confidence that New Zealand will step up to where you feel it should be?

It is a very promising development and the new government is certainly talking the talk.

I'll feel some confidence when I see them walking the walk, making actual policy changes and legislative incentives to move our economy and society in the right direction.

READ MORE: Climate change: five ways it could harm us
When it comes to tackling climate change, do you see our primary-based economy as being at odds with making meaningful gains? How can we hope to address climate change at home when half of greenhouse gas emissions come from agriculture, and our marine estate could hold vast, untapped reserves of oil and gas that could benefit our country?

The majority of the growth in our emissions over the past 25 years has come from transport and industry.

The global profile of emissions is dominated by the big emitters, but on a per-capita basis, New Zealand rates as one of the worst. Photo / 123RF
The global profile of emissions is dominated by the big emitters, but on a per-capita basis, New Zealand rates as one of the worst. Photo / 123RF

We could make great strides in these areas, plus in terms of waste reduction, and afforestation – without even touching agriculture.

Those untapped oil reserves would only appear to "benefit our country" because we don't factor in the cost of the change in climate from burning those reserves.

We have subsidised fossil fuels in this way for a century and more.

There is no benefit to New Zealand from burning more fossil fuels.

What do you make of the oft-made argument that what actions we take here are relatively insignificant, given we contribute just around 0.15 per cent of global emissions and future climate depends on the big polluters. Is this true to any extent?

Of course the global profile of emissions is dominated by the big emitters.

But on a per-capita basis, New Zealand is one of the big emitters.

We are in the top 10 globally, per head of population, and there is as much of an onus on us as on the Chinese or the Americans to reduce our emissions.

Plus, there is the "soft power" angle of being a leader, showing others how it's done, that would benefit us on the international stage.

You toured the country recently to speak about climate change. Did the response suggest Kiwis are genuinely concerned about it? I note one survey a few years ago found only half of Kiwis agreed there was a scientific consensus human-driven climate change was actually happening, although more recent studies tell us awareness and acceptance of the science has been growing.

Yes.

We had full houses almost everywhere we went and the questions suggested strongly that those who came out to hear us are very interested and very concerned.

But, across the broader population, it's harder to say.

Because there's been no political leadership, most people probably give it very little thought and are more apathetic than concerned or dismissive.

The West Antarctic Ice Sheet - which holds the equivalent of several metres of sea level rise - is responding to climate change. Photo / File
The West Antarctic Ice Sheet - which holds the equivalent of several metres of sea level rise - is responding to climate change. Photo / File

That aside, does New Zealand still have a sceptic problem? Are there still too many Kiwis who reject the scientific consensus?

There are some, but I suspect it's a minority.

I receive regular emails telling me I have the science wrong, but they come from a very small number of individuals.

READ MORE: The Big Read: Our slow-moving disaster as sea level rises

I'd say the major issue is that most people don't even think about it.

So how hopeful are you, actually, that the world will avert the worst possible effects of climate change? Where do you place your optimism on a scale of one to 10?

I am hopeful we can avoid the real worst-case scenario but I am pessimistic about the 1.5C or even 2C limit.

My gut feeling is that we won't stop the warming until we are committed to 2.5C or even 3C of temperature rise.

That would lock in loss of the West Antarctic ice sheet, plus most of Greenland and part of the east Antarctic and would commit the globe to 10m or more of sea level rise.

Plus of course a big rise in extreme high temperatures, droughts, floods and crop failures.

Because of the delay time built into the climate system, it's my feeling that we won't take decisive action until a lot of change is baked in, so we'll have a great deal of adapting to do.

On a scale of one to 10 for optimism, I'm about a three.

I would love to be pleasantly surprised.

The Series

MONDAY:

Our rivers

TODAY:

Our climate

TOMORROW:

Our nature

THURSDAY:

Our biosecurity

FRIDAY:

Our oceans