Arctic ice loss is worrying, but the giant stirring in the South could be even worse



Field camp on the East Antarctic ice sheet.
Nerilie Abram

Nerilie Abram, Australian National University; Matthew England, UNSW, and Matt King, University of Tasmania

A record start to summer ice melt in Greenland this year has drawn attention to the northern ice sheet. We will have to wait to see if 2019 continues to break ice-melt records, but in the rapidly warming Arctic the long-term trends of ice loss are clear.

But what about at the other icy end of the planet?

Antarctica is an icy giant compared to its northern counterpart. The water frozen in the Greenland ice sheet is equivalent to around 7 metres of potential sea level rise. In the Antarctic ice sheet there are around 58 metres of sea-level rise currently locked away.

Like Greenland, the Antarctic ice sheet is losing ice and contributing to unabated global sea level rise. But there are worrying signs Antarctica is changing faster than expected and in places previously thought to be protected from rapid change.

The threat from beneath

On the Antarctic Peninsula – the most northerly part of the Antarctic continent – air temperatures over the past century have risen faster than any other place in the Southern Hemisphere. Summer melting already happens on the Antarctic Peninsula between 25 and 80 days each year. The number of melt days will rise by at least 50% when global warming hits the soon-to-be-reached 1.5℃ limit set out in the Paris Agreement, with some predictions pointing to as much as a 150% increase in melt days.

But the main threat to the Antarctic ice sheet doesn’t come from above. What threatens to truly transform this vast icy continent lies beneath, where warming ocean waters (and the vast heat carrying capacity of seawater) have the potential to melt ice at an unprecedented rate.




Read more:
New findings on ocean warming: 5 questions answered


Almost all (around 93%) of the extra heat human activities have caused to accumulate on Earth since the Industrial Revolution lies within the ocean. And a large majority of this has been taken into the depths of the Southern Ocean. It is thought that this effect could delay the start of significant warming over much of Antarctica for a century or more.

However, the Antarctic ice sheet has a weak underbelly. In some places the ice sheet sits on ground that is below sea level. This puts the ice sheet in direct contact with warm ocean waters that are very effective at melting ice and destabilising the ice sheet.

Scientists have long been worried about the potential weakness of ice in West Antarctica because of its deep interface with the ocean. This concern was flagged in the first report of the Intergovernmental Panel on Climate Change (IPCC) way back in 1990, although it was also thought that substantial ice loss from Antarctica wouldn’t be seen this century. Since 1992 satellites have been monitoring the status of the Antarctic ice sheet and we now know that not only is ice loss already underway, it is also vanishing at an accelerating rate.

The latest estimates indicate that 25% of the West Antarctic ice sheet is now unstable, and that Antarctic ice loss has increased five-fold over the past 25 years. These are remarkable numbers, bearing in mind that more than 4 metres of global sea-level rise are locked up in the West Antarctic alone.

Antarctic ice loss 1992–2019, European Space Agency.




Read more:
Antarctica has lost nearly 3 trillion tonnes of ice since 1992


Thwaites Glacier in West Antarctica is currently the focus of a major US-UK research program as there is still a lot we don’t understand about how quickly ice will be lost here in the future. For example, gradual lifting of the bedrock as it responds to the lighter weight of ice (known as rebounding) could reduce contact between the ice sheet and warm ocean water and help to stabilise runaway ice loss.

On the other hand, melt water from the ice sheets is changing the structure and circulation of the Southern Ocean in a way that could bring even warmer water into contact with the base of the ice sheet, further amplifying ice loss.

There are other parts of the Antarctic ice sheet that haven’t had this same intensive research, but which appear to now be stirring. The Totten Glacier, close to Australia’s Casey station, is one area unexpectedly losing ice. There is a very pressing need to understand the vulnerabilities here and in other remote parts of the East Antarctic coast.

The other type of ice

Sea ice forms and floats on the surface of the polar oceans. The decline of Arctic sea ice over the past 40 years is one of the most visible climate change impacts on Earth. But recent years have shown us that the behaviour of Antarctic sea ice is stranger and potentially more volatile.

The extent of sea ice around Antarctica has been gradually increasing for decades. This is contrary to expectations from climate simulations, and has been attributed to changes in the ocean structure and changing winds circling the Antarctic continent.

But in 2015, the amount of sea ice around Antarctica began to drop precipitously. In just 3 years Antarctica lost the same amount of sea ice the Arctic lost in 30.




Read more:
Why Antarctica’s sea ice cover is so low (and no, it’s not just about climate change)


So far in 2019, sea ice around Antarctica is tracking near or below the lowest levels on record from 40 years of satellite monitoring. In the long-term this trend is expected to continue, but such a dramatic drop over only a few years was not anticipated.

There is still a lot to learn about how quickly Antarctica will respond to climate change. But there are very clear signs that the icy giant is awakening and – via global sea level rise – coming to pay us all a visit.The Conversation

Nerilie Abram, ARC Future Fellow, Research School of Earth Sciences; Chief Investigator for the ARC Centre of Excellence for Climate Extremes, Australian National University; Matthew England, Australian Research Council Laureate Fellow; Deputy Director of the Climate Change Research Centre (CCRC); Chief Investigator in the ARC Centre of Excellence in Climate System Science, UNSW, and Matt King, Professor, Surveying & Spatial Sciences, School of Technology, Environments and Design, University of Tasmania

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

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Global Warming and Antarctica


How solar heat drives rapid melting of parts of Antarctica’s largest ice shelf



Scientists measured the thickness and basal melt of the Ross Ice Shelf.
Supplied, CC BY-ND

Craig Stewart, National Institute of Water and Atmospheric Research

The ocean that surrounds Antarctica plays a crucial role in regulating the mass balance of the continent’s ice cover. We now know that the thinning of ice that affects nearly a quarter of the West Antarctic Ice Sheet is clearly linked to the ocean.

The connection between the Southern Ocean and Antarctica’s ice sheet lies in ice shelves – massive slabs of glacial ice, many hundreds of metres thick, that float on the ocean. Ice shelves grind against coastlines and islands and buttress the outflow of grounded ice. When the ocean erodes ice shelves from below, this buttressing action is reduced.

While some ice shelves are thinning rapidly, others remain stable, and the key to understanding these differences lies within the hidden oceans beneath ice shelves. Our recently published research explores the ocean processes that drive melting of the world’s largest ice shelf. It shows that a frequently overlooked process is driving rapid melting of a key part of the shelf.




Read more:
Ice melt in Greenland and Antarctica predicted to bring more frequent extreme weather


Ocean fingerprints on ice sheet melt

Rapid ice loss from Antarctica is frequently linked to Circumpolar Deep Water (CDW). This relatively warm (+1C) and salty water mass, which is found at depths below 300 metres around Antarctica, can drive rapid melting. For example, in the south-east Pacific, along West Antarctica’s Amundsen Sea coast, CDW crosses the continental shelf in deep channels and enters ice shelf cavities, driving rapid melting and thinning.

Interestingly, not all ice shelves are melting quickly. The largest ice shelves, including the vast Ross and Filchner-Ronne ice shelves, appear close to equilibrium. They are largely isolated from CDW by the cold waters that surround them.

The satellite image shows that strong offshore winds drive sea ice away from the north-western Ross Ice Shelf, exposing the dark ocean surface. Solar heating warms the water enough to drive melting. Figure modified from https://www.nature.com/articles/s41561-019-0356-0.
Supplied, CC BY-ND

The contrasting effects of CDW and cold shelf waters, combined with their distribution, explain much of the variability in the melting we observe around Antarctica today. But despite ongoing efforts to probe the ice shelf cavities, these hidden seas remain among the least explored parts of Earth’s oceans.




Read more:
Climate scientists explore hidden ocean beneath Antarctica’s largest ice shelf


It is within this context that our research explores a new and hard-won dataset of oceanographic observations and melt rates from the world’s largest ice shelf.

Beneath the Ross Ice Shelf

In 2011, we used a 260 metre deep borehole that had been melted through the north-western corner of the Ross Ice Shelf, seven kilometres from the open ocean, to deploy instruments that monitor ocean conditions and melt rates beneath the ice. The instruments remained in place for four years.

The observations showed that far from being a quiet back water, conditions beneath the ice shelf are constantly changing. Water temperature, salinity and currents follow a strong seasonal cycle, which suggests that warm surface water from north of the ice front is drawn southward into the cavity during summer.

Melt rates at the mooring site average 1.8 metres per year. While this rate is much lower than ice shelves impacted by warm CDW, it is ten times higher than the average rate for the Ross Ice Shelf. Strong seasonal variability in the melt rate suggests that this melting hotspot is linked to the summer inflow.

Summer sea surface temperature surrounding Antarctica (a) and in the Ross Sea (b) showing the strong seasonal warming within the Ross Sea polynya. Figure modified from https://www.nature.com/articles/s41561-019-0356-0.
Supplied, CC BY-ND

To assess the scale of this effect, we used a high-precision radar to map basal melt rates across a region of about 8,000 square kilometres around the mooring site. Careful observations at around 80 sites allowed us to measure the vertical movement of the ice base and internal layers within the ice shelf over a one-year interval. We could then determine how much of the thinning was caused by basal melting.

Melting was fastest near the ice front where we observed short-term melt rates of up to 15 centimetres per day – several orders of magnitude higher than the ice shelf average rate. Melt rates reduced with distance from the ice front, but rapid melting extended far beyond the mooring site. Melting from the survey region accounted for some 20% of the total from the entire ice shelf.

The bigger picture

Why is this region of the shelf melting so much more quickly than elsewhere? As is so often the case in the ocean, it appears that winds play a key role.

During winter and spring, strong katabatic winds sweep across the western Ross Ice Shelf and drive sea ice from the coast. This leads to the formation of an area that is free of sea ice, a polynya, where the ocean is exposed to the atmosphere. During winter, this area of open ocean cools rapidly and sea ice grows. But during spring and summer, the dark ocean surface absorbs heat from the sun and warms, forming a warm surface pool with enough heat to drive the observed melting.

Although the melt rates we observe are far lower than those seen on ice shelves influenced by CDW, the observations suggest that for the Ross Ice Shelf, surface heat is important.

Given this heat is closely linked to surface climate, it is likely that the predicted reductions in sea ice within the coming century will increase basal melt rates. While the rapid melting we observed is currently balanced by ice inflow, glacier models show that this is a structurally critical region where the ice shelf is pinned against Ross Island. Any increase in melt rates could reduce buttressing from Ross Island, increasing the discharge of land-based ice, and ultimately add to sea levels.

While there is still much to learn about these processes, and further surprises are certain, one thing is clear. The ocean plays a key role in the dynamics of Antarctica’s ice sheet and to understand the stability of the ice sheet we must look to the ocean.The Conversation

Craig Stewart, Marine Physicist, National Institute of Water and Atmospheric Research

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

Time will tell if this is a record summer for Greenland ice melt, but the pattern over the past 20 years is clear



Melting on top of sea ice off northwestern Greenland, June 2019.
Steffen M. Olsen/Twitter

Nerilie Abram, Australian National University

Greenland has been in the news a bit lately. From Huskies seemingly walking on water, to temperatures soaring to 20℃ above average for the time of year, to predictions of the vast ice sheet being lost entirely, what is going on?

At its most simple: ice melts when it gets too warm.

Of course, some ice melts every time summer rolls around, but the amount of Arctic ice that melts each summer is growing, and we’re waiting to see whether this turns out to be a record-breaking year for Greenland ice melt.

No part of the planet is free from the impacts of human-caused climate change. But Greenland, and the Arctic more generally, is experiencing the impacts particularly severely. Temperatures in the planet’s extreme north are rising twice as fast as the global average.

Amplification of climate change in the Arctic.




Read more:
Ice melt in Greenland and Antarctica predicted to bring more frequent extreme weather


Greenland is warming so rapidly because of what climate scientists refer to as a “positive feedback”. Despite the name, these are not good. A better term might be “climate change amplifier”.

The Arctic has many “positive feedbacks” or “amplifiers” that worsen the effects of climate change here. For example, as snow and ice begin to melt, the surface darkens, allowing it to absorb more heat and thus melt even more.

This effect is most dramatic when snow and ice are lost completely, as in the case of the dramatic loss of the sea ice covering the Arctic ocean. Arctic sea ice loss is one of the major factors that explains why the Arctic is warming so much faster than the rest of the planet.

Another worrisome characteristic of climate change in the Arctic is the potential for ice melt to accelerate. The temperature threshold at which ice begins to melt means that once the climate has warmed enough to start melting ice, any further warming will rapidly cause an even larger amount of melting to occur. That is the reality beginning to play out in Greenland.

Beginning of the 2019 summer melt season

Last month, ice melt across the surface of Greenland made headlines. Surface melting spiked rapidly and was unusually strong for June. Melting was most intense around the edges of the Greenland ice sheet, and about 40% of the entire ice sheet surface was affected to some extent.

Greenland ice melt is typically very irregular during each summer, spiking as weather systems bring warm air masses over the ice sheet. Given this variability, it is not yet clear whether 2019 is going to be an unusually bad year for melting over Greenland – and whether it will rival the worst year on record, 2012, when the entire surface of the ice sheet experienced melting.

But what is very clear from observations since the 1970s (and completely consistent with simple physics) is that as the Arctic climate warms, the Greenland summer melt season is starting earlier, lasting longer, and becoming more intense.

Samples of older ice from inside Greenland’s ice sheet paint an even clearer picture of the changes that climate warming is causing. The amount of summer melting first began to increase in the mid-1800s, not long after human-driven climate warming began. Summer melt over the past two decades has reached levels roughly 50% higher than before the Industrial Revolution, and the speed of ice loss from the Greenland sheet has increased nearly sixfold since the 1980s.

Greenland melt intensity over the past 350 years.




Read more:
The Industrial Revolution kick-started global warming much earlier than we realised


Choices for the future

An ice sheet has existed on Greenland for millions of years. But the geological timescales of ice sheet growth and renewal are vastly outpaced by the human-caused changes we see today.

A study published in June this year, at the same time surface melting of the ice sheet was spiking, predicts that if human greenhouse emissions continue unabated, by the end of this century ice loss from the Greenland ice sheet could see the ocean rise by up to 33cm.

If all of the Greenland ice sheet were to melt, global sea level would rise by more than 7 metres. According to the same study, that could potentially happen within 1,000 years.




Read more:
Cold and calculating: what the two different types of ice do to sea levels


The evidence is abundantly clear: the rising temperature of the planet is causing more Arctic ice to melt during the northern summer. We cannot avoid further ice loss in coming decades, and people and ecosystems will have to adapt to this.

But there is still a window of opportunity to avoid the worst impacts of future climate change in the longer term. The evidence tells us that the only way to prevent the destruction of the Greenland ice sheet, and multi-metre rises in global sea level, is to make rapid, deep cuts to greenhouse gas emissions. That is a choice we still have a chance to make.The Conversation

Nerilie Abram, ARC Future Fellow, Research School of Earth Sciences; Chief Investigator for the ARC Centre of Excellence for Climate Extremes, Australian National University

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

Sydney declares a climate emergency – what does that mean in practice?


Chris Turney, UNSW

Late on Monday night, the City of Sydney became the first state capital in Australia to officially declare a climate emergency. With climate change considered a threat to human life, Sydney councillors unanimously supported a motion put forward by Lord Mayor Clover Moore to mobilise city resources to reduce carbon emissions and minimise the impact of future change.

The decision sees Sydney join a variety of local and national governments around the world, in a movement that is increasingly gaining momentum. In total, some 658 local governments around the world have made the same declaration, with the UK and Canada committing their national governments to the global movement in just the past two months.

An official declaration of climate emergency puts a government on a “wartime mobilisation” that places climate change at the centre of policy and planning decisions.




Read more:
UK becomes first country to declare a ‘climate emergency’


While interpretations differ on what a “climate emergency” means in practice, governments have established a range of measures to help meet the targets set by the Paris climate agreement. Under this agreement, 197 countries have pledged to limit global temperature rise to less than 2℃ above pre-industrial levels, and ideally no more than 1.5℃.

With 2018 having brought all manner of record-breaking climate extremes, and global average temperatures projected to reach 3.2℃ above the pre-industrial average based on current national pledges and targets for greenhouse emissions, Sydney’s recognition of a national emergency is both highly appropriate and also a major turning-point for Australia.

Although a signatory to the Paris Agreement, Australia’s greenhouse emissions have risen over the past four years since the repeal of the carbon price. With Australian emissions most notably increasing around transport, the United Nations climate discussions currently being held in Bonn have raised concerns over the nation’s ability to meet its Paris commitments.

Economic impacts

With the global cost of inaction on climate change projected to reach a staggering US$23 trillion a year by the end of the century (equivalent to around five 2008 global financial crises every year), several nations are already ramping up their Paris Agreement commitments ahead of schedule. The UK recently announced its intention to be carbon-neutral by 2050.

Australia is particularly vulnerable to the future financial costs of climate change, with economic models suggesting losses of A$159 billion a year through the impact of sea level rise and drought-driven collapses in agricultural productivity. The cost for each household has been put at about A$14,000.




Read more:
Cutting cities’ emissions does have economic benefits – and these ultimately outweigh the costs


After Sydney’s declaration, 150 faith leaders on Tuesday signed an open letter endorsing the decision, and describing the climate issue as a moral challenge that transcends religious belief. They have called for an urgent mobilisation to reach 100% renewable energy by the year 2030, and for an end to the approval of any new coal and gas projects, including Adani’s controversial Carmichael coal mine in Queensland.

The recent court ruling against the proposed Rocky Hill coal mine in the New South Wales Hunter Valley – a decision made partly on climate grounds – could mark a crucial turning point in the fortunes of future mining projects.




Read more:
Landmark Rocky Hill ruling could pave the way for more courts to choose climate over coal


As part of its emergency declaration, Sydney has also called on the federal government to establish a “just transition authority” to support Australians currently employed in fossil fuel industries. This is an urgent issue and a crucial part of the transition to a low-emissions economy.

A major nationwide training program will be needed to help re-skill the estimated 8,000 people who work in fossil-fuelled electricity production, and to help fill the tens of thousands of new jobs in renewable energy-related fields.

With the scale of change required to decarbonise the global economy and hopefully avoid a 2℃ warmer world, the need to support communities across Australia and overseas will likely become an increasing challenge for governments around the world. Putting ourselves on an emergency footing could help provide precisely the impetus we need.The Conversation

Chris Turney, Professor of Earth Science and Climate Change, ARC Centre of Excellence for Australian Biodiversity and Heritage, UNSW

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

‘Sadness, disgust, anger’: fear for the Great Barrier Reef made climate change feel urgent



Tourists are experiencing ‘Reef grief’.
Matt Curnock, Author provided

Matt Curnock, CSIRO and Scott Heron, James Cook University

Media coverage of mass coral bleaching on the Great Barrier Reef may have been a major tipping point for public concerns around climate change, according to research published today.

Severe and extensive bleaching during the summers of 2016 and 2017 has been directly attributed to human-caused climate change. Much of the ensuing media coverage used emotional language, with many reports of the Reef dying.




Read more:
Back-to-back bleaching has now hit two-thirds of the Great Barrier Reef


While the physical effects of the bleaching have been well documented, we wanted to understand the social and cultural impact.

Our research, including a study published today in Nature Climate Change, has compared survey responses from thousands of Australians and international visitors, before and after the bleaching event.

Reef grief

Our research team conducted face-to-face interviews with 4,681 visitors to the Great Barrier Reef region, in 14 coastal towns from Cooktown to Bundaberg, over June to August in both 2013 and 2017. We asked more than 50 questions about their perceptions and values of the Reef, as well as their attitudes towards climate change.

We found a large proportion of respondents, including Australians and overseas visitors, expressed forms of grief in response to loss and damage to the iconic ecosystem. Negative emotions associated with words given in short statements about “what the Great Barrier Reef means to you”, included sadness, disgust, anger and fear.




Read more:
Hope and mourning in the Anthropocene: Understanding ecological grief


Emotional appeals are widely used in media stories and in social media campaigns, and appealing to fear in particular can heighten a story’s impact and spread online.

However, a side-effect of this approach is the erosion of people’s perceived ability to take effective action. This is called a person’s “self-efficacy”.
This effect is now well documented in reactions to representations of climate change, and is actually a barrier to positive community engagement and action on the issue.

In short, the more afraid someone is for the Great Barrier Reef, the less they may feel their individual efforts will help to protect it.

While our results show a decline in respondents’ self-efficacy, there was a corresponding increase in how highly they valued the Reef’s biodiversity, its scientific heritage and its status as an international icon. They were also more willing to support action to protect the Reef. This shows widespread empathy for the imperilled icon, and suggests greater support for collective actions to mitigate threats to the Reef.

Researchers surveyed thousands of visitors to the Great Barrier Reef in 2013 and 2017.
Matt Curnock, Author provided

Changing attitudes

We observed a significant increase in the proportion of people who believe that climate change is “an immediate threat requiring action”. In 2013 some 50% of Australian visitors to the Great Barrier Reef region agreed climate change is an immediate threat; in 2017 that rose to 67%. Among international visitors, this proportion was even higher (64% in 2013, rising to 78% in 2017).

This represents a remarkable change in public attitudes towards climate change over a relatively short period. Previous surveys of Australian climate change attitudes over 2010 to 2014 showed that aggregate levels of opinion remained stable over that time.

Comparing our findings with other recent research describing the extent of coverage and style of reporting associated with the 2016-2017 mass coral bleaching event, we infer that this event, and the associated media representations, contributed significantly to the shift in public attitudes towards climate change.

Moving beyond fear

As a source of national pride and with World Heritage status, the Great Barrier Reef will continue to be a high profile icon representing the broader climate change threat.

Media reports and advocacy campaigns that emphasise fear, loss and destruction can get attention from large audiences who may take the message of climate change on board.

But this does not necessarily translate into positive action. A more purposeful approach to public communication and engagement is needed to encourage collective activity that will help to mitigate climate change and reduce other serious threats facing the Reef.

Examples of efforts that are underway to reduce pressures on the Reef include improvements to water quality, control of crown-of-thorns starfish outbreaks, and reducing poaching in protected zones. Tourism operators on the Reef are also playing an important role in restoring affected areas, and are educating visitors about threats, to improve Reef stewardship.

Clearly there remains an immediate need to reduce greenhouse gas emissions to ensure the Reef’s World Heritage qualities are maintained for future generations.

However, maintaining hope, and offering accessible actions towards attainable goals is critical to engaging people in collective efforts, to help build a more sustainable future in which coral reefs can survive.


The authors would like to acknowledge Nadine Marshall, who co-wrote this article while employed by CSIRO. We thank our other co-authors of the Nature Climate Change paper, including Lauric Thiault (National Center for Scientific Research, PSL Université Paris), Jessica Hoey and Genevieve Williams (Great Barrier Reef Marine Park Authority), Bruce Taylor and Petina Pert (CSIRO Land and Water) and Jeremy Goldberg (CSIRO & James Cook University). The scientific results and conclusions, as well as any views or opinions expressed herein, are those of the authors and do not necessarily reflect those of the Australian Government or the Minister for the Environment, or the Queensland Government, or indicate commitment to any particular course of action.The Conversation

Matt Curnock, Social Scientist, CSIRO and Scott Heron, Senior Lecturer, James Cook University

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