With the UN climate talks in Paris nearing the crunch time, the Herald's science reporter, Jamie Morton, has been speaking to a range of experts about climate-related issues.

Here he speaks with science writer and RNZ producer Veronika Meduna, whose new book Towards A Warmer World: What Climate Change Will Mean For New Zealand's Future has just gone on sale.
Q. Why did you write this book?

I've been covering climate change research for some time but really wanted to focus on what it means for this particular region - New Zealand, the Pacific islands and the surrounding ocean.

In the book I focus on climate change impacts (as opposed to what New Zealand could/should do to reduce greenhouse gas emissions) because regardless of the outcomes at the Paris climate summit, we will all be affected by impacts that have already become inevitable.

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In the end, there's one aspect I decided not to touch on, and that's the impact of climate change on health. This is so tightly interlinked with issues of inequality and poverty, with climate change acerbating current problems, that it really deserves its own text.

Q. What, do you feel, have been the largest warning signs from the world's research community over recent times in terms of where we might be headed without action?

Rising seas, and the contribution the melting of ice sheets will make to future sea level rise. So far, the rise in sea levels (about 17cm in New Zealand, 19cm global average) we are already observing is mostly due to the warming of the oceans and the fact that warmer water expands, and the shrinking of mountain glaciers. But over the past few years, scientists have shown that warming oceans are also eating away at Antarctica's ice from below, and a lot of effort is going into working out how much this ice loss will contribute to future sea levels, how fast that will happen, and whether it will be an accelerating process.

The one impact of climate change that we can be absolutely sure of is that the oceans will continue to rise for centuries to come.Even in a decarbonised world, where we are no longer adding greenhouse gas emissions to the atmosphere and where the warming eventually reaches a peak and starts moving back towards colder temperatures, sea levels will continue to rise because it takes a lot longer to cool the oceans down again and land-based ice will continue to melt as long as temperatures remain above pre-industrial levels.

Projections for the end of this century range from about 0.3 to 0.6 metres for a low-emissions scenario, and somewhere between half a metre and almost a metre in a high-emissions world - and Antarctica could raise these predictions significantly.

Over the next several centuries, if we don't stop emissions, sea levels are likely to rise by several metres; the only uncertainty is how quickly this will occur. It's a question of when, not if. And that's a massive impact, globally.

Q. In your years with Radio New Zealand, and visiting places like Antarctica where change is at its most acute, how have you been able to get a first-person feel on this issue?

Antarctica opened my eyes to climate conditions in the past.

During my second visit to Antarctica, I joined the ANDRILL team (one of the most ambitious projects to understand past climate from the geological record) at a time when they had already drilled some 700 metres deep into the sediment on the ocean floor.
That was equivalent to travelling more than three million years back in time. It really felt like time travel - here I was touching rocks that had been deposited at a time when our earliest hominin ancestors were mastering bipedal walking.

I'm not a geologist, but I could still see the difference in the rock sequences, some pointing to icy conditions, some clearly suggesting open ocean conditions and algal blooms.

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Ice cores provide an even more direct link to past climate conditions. You can literally see the tiny bubbles that trap ancient air from tens or even hundreds of thousands of years ago.

Back in New Zealand, I took a fieldtrip to Baring Head, where NIWA scientists have been monitoring carbon dioxide concentrations in the atmosphere since the 1970s. This is the Southern Hemisphere equivalent of the Keeling Curve. In fact the measurements at Baring Head were actually initiated by the late David Keeling, who set up the CO2 measurements at the Mauna Loa Observatory in Hawaii in 1958. This site has been tracking the rise of CO2 ever since then.

All these experiences combined brought it home to me what 400 ppm of CO2 in the atmosphere actually means, and how quickly, compared to geological processes, we have raised concentrations.

Q. What weather changes might future generations of New Zealanders notice in a world an average several degrees warmer - and why was June this year a useful example?

As the atmosphere warms, it holds more water, and its potential to dump torrential rainfall increases. That's what we've seen during June this year, when Dunedin, the Kapiti Coast, Whanganui and other parts of New Zealand got as much rain as they would normally see in a month in just a day or two.

With every degree in temperature, the risk of extreme rainfall rises, but there are significant regional differences. In a warmer world, such heavy downpours and stormier weather will be the new normal, and combined with higher seas, such extreme weather events will be more likely to cause flooding, more frequently.

To give a sense of scale, even if sea level rises by only 30 centimetres (the lowest plausible rise in a decarbonised future), it means that what currently is an extremely rare flood event along the Otago coast, which normally occurs only once every 500 years, would occur once every 20 years. Our infrastructure is not designed for 500-year events.

Q. What can the past tell us about our future, in terms of the risk we face under climate change scenarios?

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There have been times in the geological past when carbon dioxide concentrations in the atmosphere were as high as they are today or higher. Likewise for average temperature.

The last time the world experienced greenhouse gas concentrations similar to those of today was about three million years ago. Geologists know this period as the Pliocene, and it is the period the ANDRILL team was investigating. Back then, average global temperatures were two to three degrees higher and sea levels around 20 metres above today's coastlines. So this is an indication of where we could be heading if we were to maintain CO2 concentrations at this level for a long period (centuries).

During the Pliocene, Antarctica's ice cover was also significantly less, which explains why sea levels were so much higher.

Q. In your book, you give an overview of what climate change will mean for different industries, especially primary and land-based industries. Can you briefly explain the potential impact on these?

New Zealand agriculture is not expected to be as badly affected by climate change as primary production in subtropical and tropical countries, because we're buffered by the Southern Ocean. But that doesn't mean it'll be plain sailing. Probably the biggest challenge is the increasing competition for water. We're seeing this already, where some farmers want to increase irrigation, in part to protect themselves against drought, but this can conflict with environmental or urban uses of water. With climate change, warmer and drier conditions mean that droughts are expected to become more frequent and severe in many parts of the country, particularly those that are already dry, but also some that aren't normally considered drought prone. We all know the collective shock that goes through the country if there is a risk of reduced dairy production in any year due to drought and government assistance programmes are kicking in. But when currently rare droughts become more normal, can we continue doing what we are doing now? And if we increase irrigation to manage those droughts, what happens to ecosystems that also critically rely on water?

Another issue for agriculture is that warmer winters make agriculture much more susceptible to new pests, as many bugs that currently get killed off by frosts make it through winter unharmed. At the other end of the year, we know that heat stress for cattle increases when maximum temperatures exceed 25 degrees. In a world that does not significantly reduce emissions, the number of days that exceed 25 degrees would rise significantly especially in the North Island.

The reduction in winter frosts is also an issue for horticulture, especially kiwifruit (the green Hayward cultivar), where plants rely on winter chill to promote bud break. This can be offset to some extent through the use of chemicals that achieve the same outcome, but it doesn't exactly strengthen our competitive market advantage of wanting to sell clean and green products. There will be shifts in where certain production can occur, and while that can be a benefit to some, it can be tough on the communities that get left behind and whose infrastructure and livelihood is all geared up to support those industries.

Q. And what will climate change mean for our native flora and fauna?

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In first instance, I expect that climate change will exacerbate existing areas of conflict. Take sea level rise for example. As communities want to protect themselves against encroaching seas, many will likely put up protective barriers such as sea walls. That will mean that coastal habitats will simply disappear, in what ecologists refer to as a "coastal squeeze' between developed areas and the ocean. Those coastal habitats are important though, not least as breeding grounds for shore birds and invertebrates.

Another example is our ongoing battle to get rid of, or at least manage, pests and weeds. In a warmer world, the more opportunistic pest and weed species might be disproportionately advantaged, and cause even more damage than they already are. Insects in particular are very sensitive to temperature. Warmer winters would make it easier for invasive wasps and ants to survive and to build up to population sizes that we haven't had to deal with so far.

Some ecologists argue that New Zealand's maritime climate conditions have exposed New Zealand's fauna to such variable conditions that they have evolved a degree of flexibility and that climate change pressures could remain secondary to the usual litany of threats: predators, competition, habitat loss.

But others point out that it is exactly those existing stresses that have pushed our wildlife into a corner already, and that climate change will make things a lot worse and push some species over the edge.

Elsewhere, there is much more abundant evidence of ecological climate change impacts and several general themes have emerged, including shifting habitats, changing breeding seasons, disrupted predator-prey relationships, and a head start for pests and weeds. But much of the flora and fauna that is the focus of research in the Northern Hemisphere - migratory birds, butterflies, deciduous trees and hibernating animals - is under-represented in New Zealand.

Here, our seabirds are the canaries in the mine, with many already struggling with changes in ocean conditions that don't provide enough food during the breeding season.
Examples include sooty shearwaters, or mutton birds, which have been in decline for 70 years. More recently the annual drop in numbers has been marked, but cannot be attributed to the annual harvest but rather to changes at sea.

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Rabbits have established at an altitude of 1800 metres on Mount Ruapehu, well above their normal altitudinal limit of 1000 metres. The suggestion is that reduced snow has contributed to this expansion.

Welcome swallows have been laying eggs about a month earlier.

The recruitment of eels into New Zealand rivers has dropped over the last three decades. Those that do arrive, do so a few weeks earlier, possibly due to changing thermal ocean fronts in their spawning grounds near Tonga.

Mosquitoes have expanded southwards, aided by warm climate windows.

The exotic pasture grass paspalum has spread southwards from Northland by 1.5 degrees in latitude in the span of little more than a decade.

Mortality in long-tailed bats is higher during warm winters, most likely because they emerge from their seasonal torpor more frequently and use up more energy at a time when there isn't yet enough food to replenish their reserves.

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And then there are the tuatara on North Brother Island in Cook Strait and their changing sex ratio. The ancient reptiles lay their eggs in hollows and the sex of the offspring depends entirely on the temperature during incubation. Warmer conditions produce more males, and the current sex ratio on the island, which supports about 500 individual tuatara, is already skewed towards males. Future temperature rise could tip the scales even further in favour of males and, as some biologists fear, ultimately result in the extinction of the population - partly because the tuatara habitat is now so restricted that they can't move anywhere cooler.

Q. You've dedicated a chapter to explaining the relationship between climate change and oceans. What are the links here, in terms of factors like rising sea levels, acidification, erosion, salinity, temperatures and large-scale correlation with the atmosphere?

The ocean is our buffer zone. About 30-40 per cent of the carbon dioxide emitted by human activities is absorbed by the ocean and thus prevented from accumulating in the atmosphere.

The ocean is also a huge thermal reservoir. It has stored more than 90% of the total increase in energy in the climate system over the past few decades, simply because water takes up more heat than air. The world would be a much hotter place already if we didn't have the oceans. For New Zealand in particular, this means that we are warming up more slowly than large continental land masses.

But these buffering functions also point to the vulnerability of the oceans: one issue is that the continued absorption of carbon dioxide makes the oceans more acidic. This is expected to have severe effects on the entire oceanic food web, as many organisms at the bottom of this web are shell-forming. If the water gets too acidic, these creatures won't be able to build adequate shells and there is a risk that major parts of the food web start to break down.

Ocean acidification is also being linked to changes in fish reproduction and the increased bleaching of coral reefs.

The other downside of the buffering capacity of the oceans is that because they are such a massive thermal reservoir, once we've heated them up, it will take many, many centuries for them to cool down again after we've decided we're too hot for comfort. So they will keep melting the polar ice sheets long after atmospheric temperatures might be coming down again once greenhouse gas emissions have dropped to zero.

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And of course, all that heat that is going into the ocean isn't going unnoticed. As warming water expands, sea levels go up. As waves reach higher along coastlines, this increases erosion and inundation during storms and king tides.

Q. It's sometimes argued New Zealand's place, in the global scheme of climate change, is small when compared with the emissions output of big polluters like China, India and the United States. Why should climate change and climate action be relevant to Kiwis?

We can't control climate change ourselves, so we rely critically on coordinated actions by others. But for this to happen, and to have our voice heard, we need to be part of the action.

As a nation, New Zealand's contribution to global greenhouse gas concentrations is small, less than 1 per cent, but that would likely be true for any other group of4.5 million people. Measured on a per-capita basis, we're right up there with the biggest polluters.

Q. Finally, with the Paris climate talks underway now, what hope do you feel we have of achieving a strong and lasting global commitment to reduce emissions?

I'm hopeful that we will get an agreement out of COP21. It may not be as strong as it could be, but there seems no room for complete failure this time. At least we should get an agreement that starts moving in the right direction, towards a low-carbon future.

I'm encouraged by the fact that many countries, including Australia, are in favour of the goal to keep warming at 1.5C above pre-industrial levels, rather than 2 degrees.

I'm equally optimistic that the groundswell in grassroots activism is an indication that more and more people are willing to make a difference.

• Veronika Meduna is a producer for RNZ's Our Changing World science show and author of the book Towards A Warmer World: What Climate Change Will Mean For New Zealand's Future, published by Bridget Williams Books and available in bookshops or as an e-book. RRP: $14.99

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