Scientists are watching the dramatic death throes of the huge Larsen B ice shelf in Antarctica, which is giving way after 10,000 years. And in only the last six years, glaciers along the Southern Antarctic Peninsula have shed 14 trillion tonnes of water.

What's going on in the big frozen continent below us? Dr Nancy Bertler of GNS Science and Victoria University, a plenary speaker in the 2015 Antarctic Science Conference opening in Christchurch tomorrow, answered these questions from the Herald.

1) We've seen some concerning developments around the continent over the past couple of years. Can you explain what large scale changes we are seeing?

Until a few years ago, we saw the Antarctic Peninsula as the canary in the coal mine because it was and is one of the fastest warming regions on Earth.


As direct consequence, we observed ice shelves catastrophically collapse.

Some of these ice shelves have been shown to have existed for more than 10,000 years and that their sudden disappearance was highly unusual.

The process that causes these collapses is that the warming of the air above the ice is sufficient to produce liquid water on the surface of these ice shelves.

This water then refreezes in cracks as it trickles down into the ice below.

When water freezes it expands and so it worked like a wedge, ultimately cracking the ice.

However, now our focus has shifted from the Antarctic Peninsula to the coast of West Antarctica.

The reason for this that an even more powerful mechanism is now causing an ever faster loss of ice and at a place where it hurts.

The easiest way to melt ice is by exposing it to water, especially warm water.
Global change, caused by the ozone hole and greenhouse gas emissions, has led to an intensification of the westerly winds and moved them southwards, closer to Antarctica.


Off the coast of West Antarctica, these powerful and persistent winds have led to the up-welling of deep waters by diverting the surface currents.

Why is this important?

The surface waters around Antarctica are very cold, almost minus 2C.

However, these deep waters are about 1C , thus 3C warmer than the usual surface waters.

This means that the West Antarctic ice sheet has its toes in a warm bath tub with the westerly winds continuing to push warm water to the coast and under the floating ice shelves.

Over the past 10 years, this caused a 70 per cent increase in mass loss of ice and concurrent acceleration in global sea level.

2) What are the big questions, however, that we still need to answer?

There are many important and exciting research questions.

However, in terms of societal relevance, there is one that stands out as particularly urgent - sea level rise from ice loss is of critical importance to our future.

The urgency might be illustrated in a simple equation.

The Intergovernmental Panel on Climate Change, the UN authority on climate change, calculated the multiplier for coastal inundations assuming 50cm sea level rise by the end of the century (a rather optimistic future; most of us would anticipate 50 cm much earlier).

For New Zealand the multiplier is at least 1000 - i.e. that the frequency of coastal inundations increases by 1000.

Assuming that all infrastructure, housing density and technology would remain the same - big assumption! - then for every $1 we currently spend on repairs for coastal damage from inundation, New Zealand would have to spend $ 1000 by the end of the century.

Ultimately, as sea levels continue to rise, we will have to retreat from many low lying regions in New Zealand and around the world.

Another very important area is around the carbon cycle.

The Southern Ocean was until very recently a very important sink for atmospheric carbon dioxide (including uptake of about 50 per cent of global CO2 emissions).

However, due to the warming of the ocean, its decrease in salinity with the additional uptake in CO2, and changes in wind pattern, the Southern Ocean is potentially at the verge of changing from an efficient sink to a potent source.

This is concerning as this will cause more of our CO2 emissions to remain in the atmosphere and in addition oceanic CO2 to be ventilated, further increasing atmospheric CO2.

This will enhance the effects of global warming, including sea level rise.

Another important area is the recovery of the ozone hole.

While it is important for the ozone hole to recover, it currently helps to cool Antarctica and has contributed to the change in surface winds.

There are important and large uncertainties on how these effects will be off-set as the ozone hole recovers and whether this might lead to an acceleration of warming in Antarctica.

Moreover, there are large questions around the terrestrial and in particular the marine ecosystems.

Scientists routinely still discover new species in the shallow and deep waters of the Southern Ocean.

At the same time these ecosystems face very large changes with a warming ocean, a decrease in salinity both from melting ice and absorption of CO2, and changes in ocean currents.

We know very little about the resilience of these ecosystem to changes as well as other threats such as commercial fishing.

3) Despite the melting, we are finding that the extent of sea ice around Antarctica is increasing. How can this be?

In 2013, we observed a strange coincide of extremes - within a few days, the Arctic sea ice extent registered a new record minimum, while in the Antarctic we measured a new record maximum.

However, the overall increase in Antarctic sea ice is not uniform, and when considered in regions becomes less of a riddle.

In West Antarctica and the Antarctic Peninsula, where we see strong atmospheric warming, a warming of the ocean due to up-welling of deep waters, and on-shore wind pushing against the shoreline, we observe the expected rapid decrease in sea ice.

However, this is off-set by a strong increase in sea ice in the Ross Sea region, New Zealand's backyard.

Here we observe a few compounding effects which are ironically also caused by global change. Most importantly perhaps, the surface waters around Antarctica are almost minus 2C.

They can be that cold and still liquid, because they are very salty.

However, if you melt ice shelves or ice sheets (frozen freshwater), the ocean water becomes less salty in these regions.

The Ross Sea region has been measured to become less salty which has been linked to melt from the Ross Ice Shelf and West Antarctic ice shelves.

This encourages the ocean to freeze more readily and thus expands sea ice. In addition, we observed an increase in off-shore winds.

This is important because these winds are cold and effective in freezing surface ocean water.

In addition, they drive sea ice out into the open ocean, causing the exposure of open ocean underneath, which then can be frozen again.

We call such places polynyas.

The Ross Sea polynya is one of the most productive sea ice production line and thus strengthening of the off-shore winds is a very effective mean of increasing sea ice there.

However, we would expect sea ice to decrease in these areas within a few decades as well as ocean temperatures continue to rise.

4) What common misconceptions are there around what's happening down there?

Antarctica is often perceived as this faraway place, inert, unchangeable, and of no consequence to people in New Zealand.

Research over the past decades has shown us that nothing could be further from the truth.
Antarctica is a highly dynamic region, which sensitively responds to and drives global change. It is one of the sensitive dials in the climate system that will shape our future.

5) Scientists trying to project sea level rise under present climate change scenarios see Antarctica as a threatening wildcard - why is this?

In 2013, carbon dioxide concentrations in the atmosphere exceeded 400 parts per million for the first time in three million years.

When we look at climate records capturing that time period 3 million years ago, we find that global sea level was 17m higher than today, which tells us that the vulnerable margins of the Antarctic and Greenland ice sheets had collapsed.

While we know that we have now created the conditions to initiate these collapses again, we are still working to determine how quickly this might happen and here we most concerned regarding West Antarctica.

Professor Bob Bindschandler, an eminent NASA scientist, summarised the problem well: "ice sheets hate water".

The easiest way to melt an ice sheet and thus raise global sea level is by exposing it to water.

Well, most of the Greenland and East Antarctic ice sheets sit on ground that is well above sea level.

This is different for West Antarctica.

Here the continent lies up to 2000m below sea level.

If you had x-ray vision and could look through the ice sheet to the underlying bedrock, West Antarctica would look like a collection of islands separated by deep ocean canyons that are currently filled with ice.

In addition, the weight of the ice sheet pushes the bedrock further down in the centre of West Antarctica where the ice is thicker.

Therefore the ice sheets looks a little bit like a soup bowl.

As the warm, deep waters, pushed by the westerly winds, nibble on the floating ice shelves, the ice retreats towards the interior of Antarctica.

By doing so, it exposes an ever thicker body of ice to the warm waters, which can now even more efficiently eat away on the ice sheet.

Modelling studies in the last two years have shown that this can lead to a runaway process.

We have confidence into these studies because the models were able to replicate the magnitude of change we observed from records 3 million years ago.

However, direct observations are very difficult - the weather is notoriously bad along this coast line, and the region lies far from any Antarctic base.

Yet scientists all around the world including New Zealand hurry to gather more data to provide an updated and improved forecast.

6) To many Kiwis, these changes might seem a little irrelevant to their everyday lives. Why should they care?

Antarctica is not only sensitive to global change but a powerful modulator of global change. In New Zealand, every 10cm of sea level rise triples the occurrence of coastal flooding.

Depending on our choices regarding greenhouse gas emissions, we expect to see at least 50-100 cm of global sea level rise by the end of the century and potentially much more as West Antarctica is starting to respond.

This in itself poses a tremendous challenge to the major cities of New Zealand and all coastal communities.

However, at the same time climate change also causes an intensification of storm surges and extreme weather event.

Even at 50cm sea level increase - which we could see within a few decades - the combined effect of sea level rise and changes in storm surges will cause flood 100 year coastal flood event to become an annual event; and an annual event to occur daily fuelled sufficiently by normal tides.

I'm not an economist but it is quite obvious that this will be hugely expensive in addition to the human tragedy.

Since the industrial revolution, global sea level rose by 20cm and New Zealand, like other regions around the world, are starting to experience an increase in such events which is consistent with the model projections.

However, Antarctica has the potential to influence in many more ways.

The ocean current flowing northward on the eastern side of New Zealand is the second largest current in the world after the circumpolar Antarctic current and is fed directly from Antarctica.

It helps to regulates global temperature and bring nutrients to New Zealand's seas, which are critical for marine ecosystem including fish stocks.

Moreover, about 50 per cent of our carbon dioxide emissions and 93 per cent of the warming caused by greenhouse gas emissions is currently absorbed by the oceans and in particular the Southern Ocean.

However, a warmer, more acidic ocean is less capable of absorbing carbon dioxide and thus could accelerate warming in the near future.

It is unclear at present whether the Southern Ocean has already switched from being an important sink for carbon dioxide to being a source.

Antarctica has been part of the New Zealand identify for a long time.

It will also be important to determine our future.

7) New Zealand can boast a leading role when it comes to Antarctic science. Can you share what achievements Kiwi researchers have made on the ice, and some of their biggest findings?

New Zealand has long and proud history of scientific discovery in Antarctica and because of its track record and innovative research is leading many high profile international efforts.

From the very early and still relevant geological mapping by New Zealand graduate students Peter Webb and Berry McKelvey in the 1950s and 60s, to the discovery of the first tetrapod - a "fourfooted", or terrestrial vertebrae - by Professor Peter Barrett, our research has dominated over many decades of scientific endeavour.

In recent decades, technology development was a critical component that allowed New Zealand's Antarctic research to lead internationally in numerous scientific disciplines.

To mind comes the highly successful ANDRILL programme which managed against all odds to recover marine sediment cores from underneath sea ice and ice shelf environments - a unique technology, New Zealand developed since the 1970s.

The records changed our understanding of the dynamic character of the West Antarctic ice sheet and showed that at 400 parts per million CO2 vulnerable regions of the ice sheet are conditioned to collapse.

Moreover, the unique long-term measurements of high atmospheric conditions at Arrival Heights near Scott Base were critical to calibrate international satellite measurements and provide a quantitative measure of total ozone.

The Latitudinal Gradient Programme brought together biological and physical scientists to investigate the unique ecosystems along the Trans-Antarctic Mountains, the first such systematic research effort.

New Zealand also undertook the first winter measurements of sea ice growth and the effects of sub ice shelf melt with students wintering over at Scott Base.

The voyages of the RV Tangaroa led to discovery of new species and mapping ecosystem conditions and played an important role in deploying US ARGO buoys which showed that the Southern Ocean is warming and all the way to the bottom.

And geophysical measurements and the cutting of actual tunnels below the ice, provided tremendous insights into the working of the ice sheets.

In terms of environmental stewardship, New Zealand led the international effort and produced one of the earliest and most stringent environmental guidelines.
New Zealand can be proud of its achievements, its contribution to science and its international partnerships.

8) At the 2015 Antarctic Science Conference, you're going to be discussing some of the work you've been leading under the Roosevelt Island Climate Evolution (RICE) project. Can you give an insight into this?

The RICE project recovered a 764m deep ice core from Roosevelt Island, at the northern edge of the vast Ross Ice Shelf.

The local ice dome is an ideal site to investigate the behaviour of the Ross Ice Shelf and with that the West Antarctic Ice Sheet in a warming world.

We are particularly interested in refining projections on how quickly and how much West Antarctica will contribute to global sea level rise in the near future - the next 10 to 200 years - and to identify noteworthy thresholds which might provide support for mitigation efforts to reduce our future carbon footprint.

RICE is a nine-nation collaboration with staff and students from over 22 institutions working on this project.

Technology development was very important for us too and we built at Victoria University the first New Zealand-ice drilling based on a Danish system but with important modifications that allowed us to obtain one of the best core qualities.

There are many lines of research which support and add to the project from the analysis of high resolution greenhouse gas records, to a chronology of Antarctic and Southern Hemisphere volcanism, to microbiological life in the ice, to atmospheric circulation pattern and marine primary productivity records.

We produced well over 100,000 discrete samples and measured many properties in real time during the core processing campaign at the National Ice Core Facility at GNS Science.

We are now at a point where many of the samples are measured and we developed a robust age scale for the record for the past 60,000 years.

Now we commence the truly exciting part of understanding the record and its interpretations. The first records tell us that the Ross Sea region has been extremely dynamic during past periods of warming indicative of large changes in ice volume, ocean temperature, sea ice extent and ultimately ice shelf retreat.

This project will keep us busy for many years to come.

9) What else will be discussed at this week's conference?

The Antarctic conference is special in that it is a meeting centred around a region rather than around a scientific discipline.

This means that there researchers presenting their work on physical sciences such as past reconstruction and modern observations of sea ice, ozone depletion, high atmosphere circulation and chemistry, ice sheet dynamics and ocean change as well as terrestrial and marine ecology, historic reconstruction, education and outreach.

I always feel very privileged to participate this conference because I don't only speak to my peers but get to see a summary into exciting research of other disciplines.

At times this can lead to new and unexpected collaborations.

10) Lastly, what future research do you hope to carry out on your next trip to the ice?

There are two obvious pathways to collapse the West Antarctic ice sheet - one via the Ross Ice Shelf which we investigate with the RICE project and the other via the West Antarctic coast line, in particular in a region called the Thwaites Glacier region, the entrance to a vast and deep ocean basin beneath the West Antarctic ice sheet.

With RICE, we not only advanced the science but tested the deployment of a small team in adverse weather conditions which was supported by Antarctica New Zealand and the US Antarctic Program.

The conditions at the Thwaites Glacier region are pretty miserable, which causes some difficulties in landing aircraft and doing work on the ground.

With RICE, scientists, engineers and logistics provides have developed a track record in working in similar conditions at a remote site and learned important lessons that have help to prepare us for this deployment.

Because of the technical and logistical challenges of this project, international collaboration is paramount to pool resources and expertise.

I led an international workshop with 12 nations represented to develop this collaboration and identify technology development needs and infrastructure requirements.

Considering the urgency of this research, I hope we will have people on the ground within the next three years.