Rising seas threaten Australia’s major airports – and it may be happening faster than we think



Sydney’s airport is one of the most vulnerable in Australia to sea level rise.
Shutterstock

Thomas Mortlock, Macquarie University; Andrew Gissing, Macquarie University; Ian Goodwin, Macquarie University, and Mingzhu Wang

Most major airports in Australia are located on reclaimed swamps, sitting only a few metres above the present day sea level. And the risk of sea level rise from climate change poses a greater threat to our airports than we’re prepared for.

In fact, some of the top climate scientists now believe global sea-level rise of over two metres by 2100 is likely under our current trajectory of high carbon emissions.




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This makes Cairns (less than 3m above sea level), Sydney and Brisbane (under 4m), and Townsville and Hobart (both around under 5m) airports among the most vulnerable.

Antarctica’s ice sheets could be melting faster than we think.
Tanya Patrick/CSIRO science image, CC BY

In the US, the National Oceanic and Atmospheric Administration (NOAA) has recommended that global mean sea level rise of up to 2.7 metres this century should be considered in planning for coastal infrastructure.

This is two to three times greater than the upper limit of recommended sea level rise projections applied in Australia.

But generally, the amount of sea level rise we can expect over the coming century is deeply uncertain. This is because ice sheet retreat rates from global warming are unpredictable.




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Given the significant disruption cost and deep uncertainty associated with the timing of sea level rise, we must adopt a risk-based approach which considers extreme sea level rise scenarios as part of coastal infrastructure planning.

Are we prepared?

As polar ocean waters warm, they can cause glaciers to melt from beneath, leading to more icebergs breaking off into the ocean and then a rapid rise in global sea level. This has happened multiple times in the Earth’s past and, on some occasions, in a matter of decades.

The Intergovernmental Panel on Climate Change (IPCC) puts sea level rise projections for Australia somewhere between 50 to 90 centimetres by 2090, relative to the average sea level measured between 1986 to 2005. But the emerging science indicates this may now be an underestimate.

Some studies suggest if substantive glacial basins of the West Antarctic Ice Sheet were to collapse, it could contribute at least a further two metres to global sea levels.

Most Australian airports have conducted risk assessments for the IPCC projections.

In fact, there is no state-level policy that considers extreme sea level rise for the most critical infrastructure, even though it is possible sea levels could exceed those recommended by the IPCC within the coming century.




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And for airports, the planning implications are stark when you compare the current projection of less than a metre of sea level rise and the potential of at least a two metre rise later this century.

Taking the most low-lying major airports in Australia as an example, our modelling suggests a collapse of the West Antarctic Ice Sheet would see their near complete inundation – without any adaptation in place.

For more elevated locations, coastal infrastructure may still be inoperable more frequently when the combined effect of storm surges, waves, elevated groundwater or river flooding are considered.

A $200 billion problem

Our airports and other forms of infrastructure near the coastline are critical to the Australian economy. The aviation industry has an estimated annual revenue of over A$43 billion, adding around A$16 billion to the economy in 2017.

While there are many uncertainties around the future cost of sea-level rise, a study by the Climate Council suggests over a metre sea level rise would put more than A$200 billion worth of Australian infrastructure at risk.

It is difficult to assign a probability and time-frame to ice sheet collapse, but scientific estimates are reducing that time frame to a century rather than a millennium.




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Uncertainty generally comes with a cost, so proactive planning would make economic sense.

Adapting our most critical coastal assets while sea levels rapidly rise is not an option – mitigation infrastructure could take decades to construct and may be prohibitively expensive.

Given the deep uncertainties associated with the timing of ice-sheet collapse, we suggest airport and other critical coastal infrastructure is subjected to risk analysis for a two to three metre sea level rise.The Conversation

Thomas Mortlock, Senior Risk Scientist, Risk Frontiers, Adjunct Fellow, Macquarie University; Andrew Gissing, General Manager, Risk Frontiers, Adjunct Fellow, Macquarie University; Ian Goodwin, Associate Professor, Macquarie University, and Mingzhu Wang, Senior Geospatial Scientist, Risk Frontiers, Adjunct Fellow, Macquarie University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Climate change forced these Fijian communities to move – and with 80 more at risk, here’s what they learned


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Many houses were flattened after Tropical Cyclone Evan, leading to the partial relocation of the Fijian viillage Denimanu.
Rowena Harbridge/AusAID, CC BY-SA

Annah Piggott-McKellar, The University of Queensland; Karen Elizabeth McNamara, The University of Queensland, and Patrick D. Nunn, University of the Sunshine Coast

The original Fijian village of Vunidogoloa is abandoned. Houses, now dilapidated, remain overgrown with vegetation. Remnants of an old seawall built to protect the village is a stark reminder of what climate change can do to a community’s home.

Vunidogoloa is one of four Fijian communities that have been forced to relocate from the effects of climate change. And more than 80 communities have been earmarked by the Fiji government for potential future relocation.




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Low lying coastal communities like these are especially vulnerable to threats of sea-level rise, inundation of tides, increased intensity of storm surges and coastal erosion. Extreme, sudden weather events such as cyclones can also force communities to move, particularly in the tropics.

But relocating communities involves much more than simply rebuilding houses in a safer location.

It involves providing the right conditions for people to rebuild the lives they knew, such as equitable access to resources and services, social capital and community infrastructure.

Our research documents the experiences and outcomes of relocation for two of these Fijian communities – Vunidogoloa and Denimanu.

The relocated villages

My colleagues and I visited Vunidogoloa and Denimanu, villages in Fiji’s Northern Islands, at the end of 2017 and spoke to village leaders and community members to learn how they felt about the relocation process.

All 153 residents of Vunidogoloa and roughly half of the 170 people in Denimanu moved away from their climate ravaged homes.

Map of Fiji showing the two case study sites.
Author provided

Flooding in Vunidogoloa

Vunidogoloa is a classic example of the slow creep of climate change. For a number of decades the residents have fought coastal flooding, salt-water intrusion and shoreline erosion. The village leaders approached the Fijian government, asking to be relocated to safer ground.

The relocation was originally set for 2012 but, after delays, the entire village moved roughly 1.5 kilometres inland two years later. This is often recognised as the first ever village in Fiji to relocate from climate change.

The new village relocation site of Vunidogoloa.

Cyclone in Denimanu

In contrast to Vunidogoloa, Denimanu experienced sudden onset effects of climate change.

While the village had been experiencing encroaching shorelines for years, it was Tropical Cyclone Evan, which hit in 2012 destroying 19 houses closest to the shoreline, that prompted relocation.




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These homes were rebuilt roughly 500 metres from the original site on a hill slope. With the remaining houses still standing on the original site, the village was only partially moved.

The new village relocation site of Denimanu.
Author provided

Was relocation a success?

The relocation was a success in Vunidogoloa, and residents said they now feel much safer from climate change hazards. One villager told us:

We were so fearful because of the tides living at the old site. We were happy to move away from that fear.

But in Denimanu, where the relocated villagers live on a slope, fears of coastal threats have now been replaced by a fear of potential landslides. This is especially concerning as the village’s primary school was recently destroyed by a nearby landslide.

A relocated Denimanu local said:

We were delighted with the move to the new houses, but we were still worried about the landslide because the houses were on the hill and we know this place.

The landslide that destroyed the primary school in Denimanu village.

Ultimately, residents in both villages were happy with many aspects of the relocation process.

For example, they were provided solar power, rainwater tanks, and household facilities that weren’t available in the original villages. Vunidogoloa also received pineapple plants, cattle, and fish ponds, which have helped reestablish their livelihoods.

But it’s not all good news. While new housing was built for the community, they were built to a poor standard, with leaking through the doors and walls, especially in periods of high rainfall. Fiji is located in the tropics, so these infrastructure problems are likely to get worse.




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And moving the Vunidogoloa villagers away from the ocean might damage their livelihoods, as fishing is one of their dominant sources of food. The ocean also provides an important spiritual connection for local people.

The impacts of climate change are set to rise, especially if global action to halt greenhouse gas emissions stagnates. More vulnerable communities will need to move away from their current homes.

While relocating communities to safer, less exposed areas is one option to help people manage climate hazards, it’s not a viable solution for all those affected.

Our research shows relocation must be done in a manner that accounts for the rebuilding of local livelihoods, with sustainable adaptation solutions that put local priorities at the centre of this process.

And we need them before more coastal villages are impacted by both slow and sudden onset climate impacts, putting more people in danger.The Conversation

Annah Piggott-McKellar, PhD Candidate, The University of Queensland; Karen Elizabeth McNamara, Senior lecturer, The University of Queensland, and Patrick D. Nunn, Professor of Geography, School of Social Sciences, University of the Sunshine Coast

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Rising seas allow coastal wetlands to store more carbon



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Carbon storage in Australian mangroves can help mitigate climate change.
Shutterstock

Kerrylee Rogers, University of Wollongong; Jeffrey Kelleway, Macquarie University, and Neil Saintilan, Macquarie University

Coastal wetlands don’t cover much global area but they punch well above their carbon weight by sequestering the most atmospheric carbon dioxide of all natural ecosystems.

Termed “blue carbon ecosystems” by virtue of their connection to the sea, the salty, oxygen-depleted soils in which wetlands grow are ideal for burying and storing organic carbon.

In our research, published today in Nature, we found that carbon storage by coastal wetlands is linked to sea-level rise. Our findings suggest as sea levels rise, these wetlands can help mitigate climate change.

Sea-level rise benefits coastal wetlands

We looked at how changing sea levels over the past few millennia has affected coastal wetlands (mostly mangroves and saltmarshes). We found they adapt to rising sea levels by increasing the height of their soil layers, capturing mineral sediment and accumulating dense root material. Much of this is carbon-rich material, which means rising sea levels prompt the wetlands to store even more carbon.

We investigated how saltmarshes have responded to variations in “relative sea level” over the past few millennia. (Relative sea level is the position of the water’s edge in relation to the land rather than the total volume of water within the ocean, which is called the eustatic sea level.)




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What does past sea-level rise tell us?

Global variation in the rate of sea-level rise over the past 6,000 years is largely related to the proximity of coastlines to ice sheets that extended over high northern latitudes during the last glacial period, some 26,000 years ago.

As ice sheets melted, northern continents slowly adjusted elevation in relation to the ocean due to flexure of the Earth’s mantle.

Karaaf Wetlands in Victoria, Australia.
Boobook48/flickr, CC BY-NC-SA

For much of North America and Europe, this has resulted in a gradual rise in relative sea level over the past few thousand years. By contrast, the southern continents of Australia, South America and Africa were less affected by glacial ice sheets, and sea-level history on these coastlines more closely reflects ocean surface “eustatic” trends, which stabilised over this period.

Our analysis of carbon stored in more than 300 saltmarshes across six continents showed that coastlines subject to consistent relative sea-level rise over the past 6,000 years had, on average, two to four times more carbon in the upper 20cm of sediment, and five to nine times more carbon in the lower 50-100cm of sediment, compared with saltmarshes on coastlines where sea level was more stable over the same period.

In other words, on coastlines where sea level is rising, organic carbon is more efficiently buried as the wetland grows and carbon is stored safely below the surface.

Give wetlands more space

We propose that the difference in saltmarsh carbon storage in wetlands of the southern hemisphere and the North Atlantic is related to “accommodation space”: the space available for a wetland to store mineral and organic sediments.

Coastal wetlands live within the upper portion of the intertidal zone, roughly between mean sea level and the upper limit of high tide.

These tidal boundaries define where coastal wetlands can store mineral and organic material. As mineral and organic material accumulates within this zone it creates layers, raising the ground of the wetlands.

The coastal wetlands of Broome, Western Australia.
Shutterstock

New accommodation space for storage of carbon is therefore created when the sea is rising, as has happened on many shorelines of the North Atlantic Ocean over the past 6,000 years.

To confirm this theory we analysed changes in carbon storage within a unique wetland that has experienced rapid relative sea-level rise over the past 30 years.




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When underground mine supports were removed from a coal mine under Lake Macquarie in southeastern Australia in the 1980s, the shoreline subsided a metre in a matter of months, causing a relative rise in sea level.

Following this the rate of mineral accumulation doubled, and the rate of organic accumulation increased fourfold, with much of the organic material being carbon. The result suggests that sea-level rise over the coming decades might transform our relatively low-carbon southern hemisphere marshes into carbon sequestration hot-spots.

How to help coastal wetlands

The coastlines of Africa, Australia, China and South America, where stable sea levels over the past few millennia have constrained accommodation space, contain about half of the world’s saltmarshes.

Saltmarsh on the shores of Westernport Bay in Victoria.
Author provided

A doubling of carbon sequestration in these wetlands, we’ve estimated, could remove an extra 5 million tonnes of CO₂ from the atmosphere per year. However, this potential benefit is compromised by the ongoing clearance and reclamation of these wetlands.

Preserving coastal wetlands is critical. Some coastal areas around the world have been cut off from tides to lessen floods, but restoring this connection will promote coastal wetlands – which also reduce the effects of floods – and carbon capture, as well as increase biodiversity and fisheries production.




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In some cases, planning for future wetland expansion will mean restricting coastal developments, however these decisions will provide returns in terms of avoided nuisance flooding as the sea rises.

Finally, the increased carbon storage will help mitigate climate change. Wetlands store flood water, buffer the coast from storms, cycle nutrients through the ecosystem and provided vital sea and land habitat. They are precious, and worth protecting.


The authors would like to acknowledge the contribution of their colleagues, Janine Adams, Lisa Schile-Beers and Colin Woodroffe.The Conversation

Kerrylee Rogers, Associate Professor, University of Wollongong; Jeffrey Kelleway, Postdoctoral Research Fellow in Environmental Sciences, Macquarie University, and Neil Saintilan, Head, Department of Environmental Science, Macquarie University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

For Pacific Island nations, rising sea levels are a bigger security concern than rising Chinese influence



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Malcolm Turnbull promised to ‘step up’ Australian engagement with the Pacific last year. Will it continue now that he’s gone?
Lukas Coch/AAP

Michael O’Keefe, La Trobe University

When the Pacific Islands Forum is held in Nauru from September 1, one of the main objectives will be signing a wide-ranging security agreement that covers everything from defence and law and order concerns to humanitarian assistance and disaster relief.

The key question heading into the forum is: can the agreement find a balance between the security priorities of Australia and New Zealand and the needs of the Pacific Island nations?

Even though new Prime Minister Scott Morrison is not attending the forum, sending Foreign Minister Marise Payne instead, the Biketawa Plus security agreement remains a key aim for Canberra.




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The original Biketawa Declaration was developed as a response to the 2000 coup in Fiji. It has served Australia and the region well, providing a framework for collective action when political tensions and crises occur. However, in the face of rapid change, it looks narrow and dated.

Why act now? The rationale is clear. Much has happened to alter the security landscape in the Pacific since 2000. But despite the commentary in Australia, security in the Pacific is not all about geopolitics. While Australia may be most worried about China’s rising influence in the region, it would be a mistake to think this is the primary preoccupation of Pacific leaders, too.

A focus on climate change as a security issue

One key reason for updating Biketawa is to realign Australia’s security interests with those of Pacific Island countries that have grown more aware of their shared interests and confident in expressing them in international relations. This growing confidence is clear in the lobbying of Pacific nations for climate change action at the United Nations and in Fiji’s role as president of the UN’s COP23 climate talks.

In the absence of direct military threats, the Pacific Island nations are most concerned about security of a different kind. Key issues for the region are sustainable growth along a “blue-green” model, climate change (especially the increasing frequency and intensity of natural disasters and rising sea levels), illegal fishing and over-fishing, non-communicable diseases (NCDs), transnational crime, money laundering and human trafficking.




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Some of these security issues can be addressed by redirecting more Australian military forces to the region. Indeed, “disaster diplomacy” has been an effective method of connecting Australia’s security interests with those of Pacific Island nations in the past.

However, other priorities for the Pacific seem to run counter to Australia’s current policies toward the region. For example, the Pacific’s sustainable “blue-green” development agenda seems incompatible with an export-oriented growth model that is often touted by Australia as an “aid for trade” solution to Pacific “problems”.

Climate change adaptation and mitigation must also be elevated to the top of the agenda in Australia’s relations with the region. It is the most pressing problem in the Pacific, but for political and economic reasons, it hasn’t resonated to the same extent with Canberra.

In fact, Australia has recently been identified as the worst-performing country in the world on climate action. This has not gone unnoticed in the Pacific. Fiji’s prime minister, in particular, has been clear in highlighting that Australia’s “selfish” stance on climate change undermines its credibility in the region.

These shifting priorities in the Pacific present a greater challenge for Australia, especially now that there are more players in the region, such as China, Russia and Indonesia. Australia may see these “outsiders” as potential threats, but Pacific nations are just as likely to view them as alternative development partners able to provide opportunities.

New Coalition team on the Pacific

Making matters even trickier is the leadership shake-up in Canberra. What’s perhaps most problematic is Julie Bishop’s departure as foreign minister. Bishop did more to engage with Pacific countries than any foreign minister in recent memory. The [2017 Foreign Policy White Paper], for example, prioritised increased Pacific engagement and led to the region receiving the lion’s share of Australia’s latest aid budget.

Payne will attend the Pacific Islands Forum on her first overseas visit as foreign minister. As the former defence minister, she lobbied for Australia to be seen as a “security partner of choice” in the Pacific. What remains to be seen is whether she can maintain the momentum on Biketawa Plus.




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So the challenge for the new Coalition leadership is to find a way to push through a new Pacific security agreement that caters to both Australia’s security concerns about Chinese influence in the region and the Pacific Island countries’ focus on climate change and sustainable growth.

There are lessons that can be drawn from the decade-long negotiations between Australia, New Zealand and the Pacific Island nations over the Pacer Plus free-trade agreement, which was finally signed last year (without the region’s two largest economies, Papua New Guinea and Fiji). Australia must not underestimate the diplomatic skills of Pacific leaders or offer benefits that are perceived as being more attractive to it than the Pacific states.

Australia must also avoid allowing the leadership spill to impact its Pacific agenda at this sensitive time. Bishop’s focus on labour mobility between the Pacific islands and Australia has been most welcome, but there can be no authentic engagement with the region without addressing climate insecurity as well.The Conversation

Michael O’Keefe, Head of Department, Politics and Philosophy, La Trobe University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Rising seas will displace millions of people – and Australia must be ready


Jane McAdam, UNSW and John Church, UNSW

Sea-level rise is already threatening some communities around the world, particularly small island states, as it exacerbates disasters resulting from storm surges and flooding.

If greenhouse gas emissions continue unabated, by 2100 the world could see sea-level rise of a metre – or even more if there is a larger contribution from the Antarctic ice sheet, as some recent findings suggest.

Even without a larger Antarctic response, the rate of rise at the end of the 21st century for unmitigated emissions is likely to be equivalent to the rate of rise during the last deglaciation of the Earth, when sea level rose at more than a metre per century for many millennia. For all scenarios, sea-level rise will continue for centuries to come.




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Without significantly more effective mitigation than currently planned, the rise will ultimately be many metres, or even tens of metres – the question is not if there will be large rises, but how quickly they will happen.

Forcing people from their homes

As well as causing seas to rise, climate change may also increase the severity of events like cyclones and rainfall, which may force people from their homes in many regions.




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Global statistics on the risk of disaster displacement were not systematically collected until 2008, but already they offer stark figures. In 2017, 18.8 million people were internally displaced by natural disasters, with floods accounting for 8.6 million. By contrast, 11.8 million were displaced by conflict. Many more people are displaced each year by disasters than by conflict. Climate change intensifies this risk.

Roughly 100 million people live within about a metre of current high tide level. (Double these numbers for a five-metre sea-level rise, and triple them for 10 metres.)

Many of the world’s megacities are on the coast and vulnerable to sea-level change. Without adaption, it is estimated that by 2100 some of these areas will flood, displacing in the order of 100 million people.

While the vast majority of those people will never cross an international border, some will – and their legal status will be precarious because they will not qualify as refugees under the UN Refugee Convention (people with a well-founded fear of being persecuted for reasons of race, religion, nationality, political opinion or membership of a particular social group).




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In the current political climate, governments are reticent to create a new legal status for such people, and it would be difficult to encapsulate the complexity of climate change and disaster-related movement in a treaty definition anyway. Many factors drive people to leave their homes – such as poverty, resource scarcity and lack of livelihood opportunities – but climate change becomes the straw that breaks the camel’s back.

Good policy is essential

The most effective way to reduce the number of displaced people is strong global mitigation of emissions. In Australia, a successful NEG policy that included emissions reduction would cover about a third of Australia’s emissions. Mitigation policies also need to be developed to cover all emission sectors.

However, even with strong mitigation, adaptation will be essential. The evidence tells us that most people want to remain in their homes for as long as they can, and to return as quickly as possible. We therefore need laws and policies that permit people to remain in their homes where possible and desirable; that enable them to move elsewhere, before disaster strikes, if they wish; and to receive assistance and protection if they are displaced.

Coastal communities could live more effectively with rising sea levels by developing infrastructure, adopting and enforcing appropriate planning and building codes, and controlling flooding to allow sediment deposition. Storm-surge shelters and storm-surge warnings have already saved thousands of lives in countries like Bangladesh.

Good policy is essential. Studies of floods in Bangladesh showed that when people received prompt and adequate assistance, they were more likely to stay and rebuild than to move on in search of work to survive. By contrast, a year after Typhoon Haiyan struck the Philippines, tens of thousands of people remained displaced because the authorities said it was unsafe to go home but could not offer any alternative. This is likely to be a growing challenge with on-going climate change.




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We are going to see more and more climate related disasters. We can do better in the way we prepare for and respond to them. The nature and timing of policy interventions will be crucial in determining outcomes after a disaster, because together they affect people’s ability to cope and be resilient. We need a broad, complementary set of policy strategies to assist people and give them choices.


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The Conversation

On Thursday 24 August Jane McAdam and John Church will join Walter Kaelin to talk on Good Evidence, Bad Politics. This event is free to the public.

Jane McAdam, Scientia Professor and Director of the Kaldor Centre for International Refugee Law, UNSW and John Church, Chair professor, UNSW

This article was originally published on The Conversation. Read the original article.

Antarctica has lost 3 trillion tonnes of ice in 25 years. Time is running out for the frozen continent



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As the world prevaricates over climate action, Antarctica’s future is shrouded in uncertainty.
Hamish Pritchard/British Antarctic Survey

Steve Rintoul, CSIRO and Steven Chown, Monash University

Antarctica lost 3 trillion tonnes of ice between 1992 and 2017, according to a new analysis of satellite observations. In vulnerable West Antarctica, the annual rate of ice loss has tripled during that period, reaching 159 billion tonnes a year. Overall, enough ice has been lost from Antarctica over the past quarter-century to raise global seas by 8 millimetres.

What will Antarctica look like in the year 2070, and how will changes in Antarctica impact the rest of the globe? The answer to these questions depends on choices we make in the next decade, as outlined in our accompanying paper, also published today in Nature.




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Our research contrasts two potential narratives for Antarctica over the coming half-century – a story that will play out within the lifetimes of today’s children and young adults.

While the two scenarios are necessarily speculative, two things are certain. The first is that once significant changes occur in Antarctica, we are committed to centuries of further, irreversible change on global scales. The second is that we don’t have much time – the narrative that eventually plays out will depend on choices made in the coming decade.

Change in Antarctica has global impacts

Despite being the most remote region on Earth, changes in Antarctica and the Southern Ocean will have global consequences for the planet and humanity.

For example, the rate of sea-level rise depends on the response of the Antarctic ice sheet to warming of the atmosphere and ocean, while the speed of climate change depends on how much heat and carbon dioxide is taken up by the Southern Ocean. What’s more, marine ecosystems all over the world are sustained by the nutrients exported from the Southern Ocean to lower latitudes.

From a political perspective, Antarctica and the Southern Ocean are among the largest shared spaces on Earth, regulated by a unique governance regime known as the Antarctic Treaty System. So far this regime has been successful at managing the environment and avoiding discord.

However, just as the physical and biological systems of Antarctica face challenges from rapid environmental change driven by human activities, so too does the management of the continent.

Antarctica in 2070

We considered two narratives of the next 50 years for Antarctica, each describing a plausible future based on the latest science.

In the first scenario, global greenhouse gas emissions remain unchecked, the climate continues to warm, and little policy action is taken to respond to environmental factors and human activities that affect the Antarctic.

Under this scenario, Antarctica and the Southern Ocean undergo widespread and rapid change, with global consequences. Warming of the ocean and atmosphere result in dramatic loss of major ice shelves. This causes increased loss of ice from the Antarctic ice sheet and acceleration of sea-level rise to rates not seen since the end of the last glacial period more than 10,000 years ago.

Warming, sea-ice retreat and ocean acidification significantly change marine ecosystems. And unrestricted growth in human use of Antarctica degrades the environment and results in the establishment of invasive species.

Under the high-emissions scenario, widespread changes occur by 2070 in Antarctica and the Southern Ocean, with global impacts.
Rintoul et al. 2018. Click image to enlarge.

In the second scenario, ambitious action is taken to limit greenhouse gas emissions and to establish policies that reduce human pressure on Antarctica’s environment.

Under this scenario, Antarctica in 2070 looks much like it does today. The ice shelves remain largely intact, reducing loss of ice from the Antarctic ice sheet and therefore limiting sea-level rise.

An increasingly collaborative and effective governance regime helps to alleviate human pressures on Antarctica and the Southern Ocean. Marine ecosystems remain largely intact as warming and acidification are held in check. On land, biological invasions remain rare. Antarctica’s unique invertebrates and microbes continue to flourish.

Antarctica and the Southern Ocean in 2070, under the low-emissions (left) and high-emissions (right) scenarios. Each of these systems will continue to change after 2070, with the magnitude of the change to which we are committed being generally much larger than the change realised by 2070.
Rintoul et al. 2018. Click image to enlarge.

The choice is ours

We can choose which of these trajectories we follow over the coming half-century. But the window of opportunity is closing fast.

Global warming is determined by global greenhouse emissions, which continue to grow. This will commit us to further unavoidable climate impacts, some of which will take decades or centuries to play out. Greenhouse gas emissions must peak and start falling within the coming decade if our second narrative is to stand a chance of coming true.

If our more optimistic scenario for Antarctica plays out, there is a good chance that the continent’s buttressing ice shelves will survive and that Antarctica’s contribution to sea-level rise will remain below 1 metre. A rise of 1m or more would displace millions of people and cause substantial economic hardship.

Under the more damaging of our potential scenarios, many Antarctic ice shelves will likely be lost and the Antarctic ice sheet will contribute as much as 3m of sea level rise by 2300, with an irreversible commitment of 5-15m in the coming millennia.

The ConversationWhile challenging, we can take action now to prevent Antarctica and the world from suffering out-of-control climate consequences. Success will demonstrate the power of peaceful international collaboration and show that, when it comes to the crunch, we can use scientific evidence to take decisions that are in our long-term best interest.

The choice is ours.

Steve Rintoul, Research Team Leader, Marine & Atmospheric Research, CSIRO and Steven Chown, Professor of Biological Sciences, Monash University

This article was originally published on The Conversation. Read the original article.

Ocean waves and lack of sea ice can trigger Antarctic ice shelves to disintegrate


Luke Bennetts, University of Adelaide; Rob Massom, and Vernon Squire

Large waves after the loss of sea ice can trigger Antarctic ice shelf disintegration over a period of just days, according to our new research.

With other research also published today in Nature showing that the rate of annual ice loss from the vulnerable Antarctic Peninsula has quadrupled since 1992, our study of catastrophic ice shelf collapses during that time shows how the lack of a protective buffer of sea ice can leave ice shelves, already weakened by climate warming, wide open to attack by waves.




Read more:
Antarctica has lost 3 trillion tonnes of ice in 25 years. Time is running out for the frozen continent


Antarctica is covered by an ice sheet that is several kilometres thick in places. It covers an area of 14 million square kilometres – roughly twice the size of Australia. This ice sheet holds more than 90% of the world’s ice, which is enough to raise global mean sea level by 57 metres.

As snow falls and compacts on the ice sheet, the sheet thickens and flows out towards the coast, and then onto the ocean surface. The resulting “ice shelves” (and glacier tongues) buttress three-quarters of the Antarctic coastline. Ice shelves act as a crucial braking system for fast-flowing glaciers on the land, and thus moderate the ice sheet’s contribution to sea-level rise.

In the southern summer of 2002, scientists monitoring the Antarctic Peninsula (the northernmost part of mainland Antarctica) by satellite witnessed a dramatic ice shelf disintegration that was stunning in its abruptness and scale. In just 35 days, 3,250 square km of the Larsen B Ice Shelf (twice the size of Queensland’s Fraser Island) shattered, releasing an estimated 720 billion tonnes of icebergs into the Weddell Sea.

This wasn’t the first such recorded event. In January 1995, roughly 1,500 square km of the nearby Larsen A Ice Shelf suddenly disintegrated after several decades of warming and years of gradual retreat. To the southwest, the Wilkins Ice Shelf suffered a series of strikingly similar disintegration events in 1998, 2008 and 2009 — not only in summer but also in two of the Southern Hemisphere’s coldest months, May and July.

These sudden, large-scale fracturing events removed features that had been stable for centuries – up to 11,500 years in the case of Larsen B. While ice shelf disintegrations don’t directly raise sea level (because the ice shelves are already floating), the removal of shelf ice allows the glaciers behind them to accelerate their discharge of land-based ice into the ocean – and this does raise sea levels. Previous research has shown that the removal of Larsen B caused its tributary glaciers to flow eight times faster in the year following its disintegration.




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The ocean around ice shelves is typically covered by a very different (but equally important) type of ice, called sea ice. This is formed from frozen seawater and is generally no more than a few metres thick. But it stretches far out into the ocean, doubling the area of the Antarctic ice cap when at its maximum extent in winter, and varying in extent throughout the year.

The response of Antarctic sea ice to climate change and variability is complex, and differs between regions. Around the Antarctic Peninsula, in the Bellingshausen and northwestern Weddell seas, it has clearly declined in extent and annual duration since satellite monitoring began in 1979, at a similar rate to the Arctic’s rapidly receding sea ice.

The Southern Ocean is also host to the largest waves on the planet, and these waves are becoming more extreme. Our new study focuses on “long-period” swell waves (with swells that last up to about 20 seconds). These are generated by distant storms and carry huge amounts of energy across the oceans, and can potentially flex the vulnerable outer margins of ice shelves.

The earliest whalers and polar pioneers knew that sea ice can damp these waves — Sir Ernest Shackleton reported it in his iconic book South!. Sea ice thus acts as a “buffer” that protects the Antarctic coastline, and its ice shelves, from destructive ocean swells.

Strikingly, all five of the sudden major ice shelf disintegrations listed above happened during periods when sea ice was abnormally low or even absent in these regions. This means that intense swell waves crashed directly onto the vulnerable ice shelf fronts.

The straw that broke the camel’s back

The Antarctic Peninsula has experienced particularly strong climate warming (roughly 0.5℃ per decade since the late 1940s), which has caused intense surface melting on its ice shelves and exacerbated their structural weaknesses such as fractures. These destabilising processes are the underlying drivers of ice shelf collapse. But they do not explain why the observed disintegrations were so abrupt.

Our new study suggests that the trigger mechanism was swell waves flexing and working weaknesses at the shelf fronts in the absence of sea ice, to the point where they calved away the shelf fronts in the form of long, thin “sliver-bergs”. The removal of these “keystone blocks” in turn led to the catastrophic breakup of the ice shelf interior, which was weakened by years of melt.

Our research thus underlines the complex and interdependent nature of the various types of Antarctic ice – particularly the important role of sea ice in forming a protective “buffer” for shelf ice. While much of the focus so far has been on the possibility of ice shelves melting from below as the sea beneath them warms, our research suggests an important role for sea ice and ocean swells too.

The edge of an ice shelf off the Antarctic Peninsula, with floating sea ice beyond (to the left in this image).
NASA/Maria Jose Vinas

In July 2017 an immense iceberg broke away from the Larsen C Ice Shelf, just south of Larsen B, prompting fears that it could disintegrate like its neighbours.

Our research suggests that four key factors will determine whether it does: extensive flooding and fracturing across the ice shelf; reduced sea ice coverage offshore; extensive fracturing of the ice shelf front; and calving of sliver-bergs.




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If temperatures continue to rise around the Antarctic, ice shelves will become weaker and sea ice less extensive, which would imply an increased likelihood of future disintegrations.

However, the picture is not that clear-cut, as not all remaining ice shelves are likely to respond in the same way to sea ice loss and swell wave impacts. Their response will also depend on their glaciological characteristics, physical setting, and the degree and nature of surface flooding. Some ice shelves may well be capable of surviving prolonged absences of sea ice.

The ConversationIrrespective of these differences, we need to include sea ice and ocean waves in our models of ice sheet behaviour. This will be a key step towards better forecasting the fate of Antarctica’s remaining ice shelves, and how much our seas will rise in response to projected climate change over coming decades. In parallel, our new findings underline the need to better understand and model the mechanisms responsible for recent sea ice trends around Antarctica, to enable prediction of likely future change in the exposure of ice shelves to ocean swells.

Luke Bennetts, Lecturer in applied mathematics, University of Adelaide; Rob Massom, Leader, Sea Ice Group, Antarctica & the Global System program, Australian Antarctic Division and Antarctic Climate and Ecosystems CRC, and Vernon Squire, Deputy Vice-Chancellor Academic, Professor of Applied Mathematics

This article was originally published on The Conversation. Read the original article.