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.

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

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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.

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

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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.

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.

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Greenland: how rapid climate change on world’s largest island will affect us all

Dan Bach Kristensen / shutterstock

Kathryn Adamson, Manchester Metropolitan University

The largest wildfire ever recorded in Greenland was recently spotted close to the west coast town of Sisimiut, not far from Disko Island where I research retreating glaciers. The fire has captured public and scientific interest not just because its size and location came as a surprise, but also because it is yet another signpost of deep environmental change in the Arctic.

Greenland is an important cog in the global climate system. The ice sheet which covers 80% of the island reflects so much of the sun’s energy back into space that it moderates temperatures through what is known as the “albedo effect”. And since it occupies a strategic position in the North Atlantic, its meltwater tempers ocean circulation patterns.

Most of Greenland is covered by more than a kilometre of ice.
Eric Gaba / NGDC, CC BY-SA

But Greenland is especially vulnerable to climate change, as Arctic air temperatures are currently rising at twice the global average rate. Environmental conditions are frequently setting new records: “the warmest”, “the wettest”, “the driest”.

Despite its size, the fire itself represents only a snapshot of Greenland’s fire history. It alone cannot tell us about wider Arctic climate change.

But when we superimpose these extraordinary events onto longer-term environmental records, we can see important trends emerging.

The ice sheet is melting

Between 2002 and 2016 the ice sheet lost mass at a rate of around 269 gigatonnes per year. One gigatonne is one billion tonnes. One tonne is about the weight of a walrus.

Leave my weight out of this.
BMJ / shutterstock

During the same period, the ice sheet also showed some unusual short-term behaviour. The 2012 melt season was especially intense – 97% of the ice sheet experienced surface melt at some point during the year. Snow even melted at its summit, the highest point in the centre of the island where the ice is piled up more than 3km above sea level.

Change in total mass of the Greenland Ice Sheet (in Gt) from 2002 to 2016. Red crosses indicate the values every April.
NOAA

In April 2016 Greenland saw abnormally high temperatures and its earliest ever “melt event” (a day in which more than 10% of the ice sheet has at least 1mm of surface melt). Early melting doesn’t usher in a period of complete and catastrophic change – the ice won’t vanish overnight. But it does illustrate how profoundly and rapidly the ice sheet can respond to rising temperatures.

Permafrost is thawing

Despite its icy image, the margins of Greenland are actually quite boggy, complete with swarms of mosquitoes. This is the “active layer”, made up of peaty soil and sediment up to two metres thick, which temporarily thaws during the summer. The underlying permafrost, which can reach depths of 100m, remains permanently frozen.

Fighting off the mosquitos in boggy Greenland.
Kathryn Adamson, Author provided

In Greenland, like much of the Arctic, rising temperatures are thawing the permafrost. This means the active layer is growing by up to 1.5cm per year. This trend is expected to continue, seeing as under current IPCC predictions, Arctic air temperatures will rise by between 2.0°C and 7.5°C this century.

Arctic permafrost contains more than 1,500 billion tonnes of dead plants and animals (around 1,500 billion walrus equivalent) which we call “organic matter”. Right now, this stuff has been frozen for thousands of years. But when the permafrost thaws this organic matter will decay, releasing carbon and methane (another greenhouse gas) into the atmosphere.

If thawing continues, it’s estimated that by 2100 permafrost will emit 850-1,400 billion tonnes of CO₂ equivalent (for comparison: total global emissions in 2012 was 54 billion tonnes of CO₂ equivalent). All that extra methane and carbon of course has the potential to enhance global warming even further.

With this in mind, it is clear to see why the recent wildfire, which was burning in dried-out peat in the active layer, was especially interesting to researchers. If Greenland’s permafrost becomes increasingly degraded and dry, there is the potential for even bigger wildfires which would release vast stores of greenhouse gases into the atmosphere.

Species are adapting to a changing ecosystem

Major changes in the physical environment are already affecting the species that call Greenland home. Just look at polar bears, the face of Arctic climate change. Unlike other bears, polar bears spend most of their time at sea, which explains their Latin name Ursus maritimus. In particular they rely on sea ice as it gives them a deep-water platform from which to hunt seals.

However, since 1979 the extent of sea ice has decreased by around 7.4% per decade due to climate warming, and bears have had to adjust their habitat use. With continued temperature rise and sea ice disappearance, it’s predicted that populations will decline by up to 30% in the next few decades, taking the total number of polar bears to under 9,000.

Where are you, seals?
Mario_Hoppmann / shutterstock

I have considered only a handful of the major environmental shifts in Greenland over the past few decades, but the effects of increasing temperatures are being felt in all parts of the earth system. Sometimes these are manifest as extreme events, at others as slow and insidious changes.

The different parts of the environmental jigsaw interact, so that changes in one part (sea ice decline, say) influence another (polar bear populations). We need to keep a close eye on the system as a whole if we are to make reliable interpretations – and meaningful plans for the future.

Kathryn Adamson, Senior Lecturer in Physical Geography, Manchester Metropolitan University

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

Greenland: how rapid climate change on world’s largest island will affect us all

Dan Bach Kristensen / shutterstock

Kathryn Adamson, Manchester Metropolitan University

The largest wildfire ever recorded in Greenland was recently spotted close to the west coast town of Sisimiut, not far from Disko Island where I research retreating glaciers. The fire has captured public and scientific interest not just because its size and location came as a surprise, but also because it is yet another signpost of deep environmental change in the Arctic.

//platform.twitter.com/widgets.js

Greenland is an important cog in the global climate system. The ice sheet which covers 80% of the island reflects so much of the sun’s energy back into space that it moderates temperatures through what is known as the “albedo effect”. And since it occupies a strategic position in the North Atlantic, its meltwater tempers ocean circulation patterns.

Most of Greenland is covered by more than a kilometre of ice.
Eric Gaba / NGDC, CC BY-SA

But Greenland is especially vulnerable to climate change, as Arctic air temperatures are currently rising at twice the global average rate. Environmental conditions are frequently setting new records: “the warmest”, “the wettest”, “the driest”.

Despite its size, the fire itself represents only a snapshot of Greenland’s fire history. It alone cannot tell us about wider Arctic climate change.

But when we superimpose these extraordinary events onto longer-term environmental records, we can see important trends emerging.

The ice sheet is melting

Between 2002 and 2016 the ice sheet lost mass at a rate of around 269 gigatonnes per year. One gigatonne is one billion tonnes. One tonne is about the weight of a walrus.

Leave my weight out of this.
BMJ / shutterstock

During the same period, the ice sheet also showed some unusual short-term behaviour. The 2012 melt season was especially intense – 97% of the ice sheet experienced surface melt at some point during the year. Snow even melted at its summit, the highest point in the centre of the island where the ice is piled up more than 3km above sea level.

Change in total mass of the Greenland Ice Sheet (in Gt) from 2002 to 2016. Red crosses indicate the values every April.
NOAA

In April 2016 Greenland saw abnormally high temperatures and its earliest ever “melt event” (a day in which more than 10% of the ice sheet has at least 1mm of surface melt). Early melting doesn’t usher in a period of complete and catastrophic change – the ice won’t vanish overnight. But it does illustrate how profoundly and rapidly the ice sheet can respond to rising temperatures.

Permafrost is thawing

Despite its icy image, the margins of Greenland are actually quite boggy, complete with swarms of mosquitoes. This is the “active layer”, made up of peaty soil and sediment up to two metres thick, which temporarily thaws during the summer. The underlying permafrost, which can reach depths of 100m, remains permanently frozen.

Fighting off the mosquitos in boggy Greenland.
Kathryn Adamson, Author provided

In Greenland, like much of the Arctic, rising temperatures are thawing the permafrost. This means the active layer is growing by up to 1.5cm per year. This trend is expected to continue, seeing as under current IPCC predictions, Arctic air temperatures will rise by between 2.0°C and 7.5°C this century.

Arctic permafrost contains more than 1,500 billion tonnes of dead plants and animals (around 1,500 billion walrus equivalent) which we call “organic matter”. Right now, this stuff has been frozen for thousands of years. But when the permafrost thaws this organic matter will decay, releasing carbon and methane (another greenhouse gas) into the atmosphere.

If thawing continues, it’s estimated that by 2100 permafrost will emit 850-1,400 billion tonnes of CO₂ equivalent (for comparison: total global emissions in 2012 was 54 billion tonnes of CO₂ equivalent). All that extra methane and carbon of course has the potential to enhance global warming even further.

With this in mind, it is clear to see why the recent wildfire, which was burning in dried-out peat in the active layer, was especially interesting to researchers. If Greenland’s permafrost becomes increasingly degraded and dry, there is the potential for even bigger wildfires which would release vast stores of greenhouse gases into the atmosphere.

Species are adapting to a changing ecosystem

Major changes in the physical environment are already affecting the species that call Greenland home. Just look at polar bears, the face of Arctic climate change. Unlike other bears, polar bears spend most of their time at sea, which explains their Latin name Ursus maritimus. In particular they rely on sea ice as it gives them a deep-water platform from which to hunt seals.

However, since 1979 the extent of sea ice has decreased by around 7.4% per decade due to climate warming, and bears have had to adjust their habitat use. With continued temperature rise and sea ice disappearance, it’s predicted that populations will decline by up to 30% in the next few decades, taking the total number of polar bears to under 9,000.

Where are you, seals?
Mario_Hoppmann / shutterstock

I have considered only a handful of the major environmental shifts in Greenland over the past few decades, but the effects of increasing temperatures are being felt in all parts of the earth system. Sometimes these are manifest as extreme events, at others as slow and insidious changes.

The different parts of the environmental jigsaw interact, so that changes in one part (sea ice decline, say) influence another (polar bear populations). We need to keep a close eye on the system as a whole if we are to make reliable interpretations – and meaningful plans for the future.

Kathryn Adamson, Senior Lecturer in Physical Geography, Manchester Metropolitan University

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

Rapid transition to clean energy will take massive social change

Mark Diesendorf, UNSW Australia

Global climate change, driven by human emissions of greenhouse gases, is already affecting the planet, with more heatwaves, droughts, wildfires and floods, and accelerating sea-level rise.

Devastating impacts on our environment, health, social justice, food production, coastal city infrastructure and economies cannot be avoided if we maintain a slow and steady transition to a zero-carbon society.

According to Stefan Rahmstorf, Head of Earth System Analysis at the Potsdam Institute for Climate Impact Research, we need an emergency response.

A big part of this response needs to be transforming the energy sector, the principal contributor to global warming in Australia and many other developed countries.

Many groups have put forward ideas to transition the energy sector away from carbon. But what are the key ingredients?

Technology is the easy bit

At first glance the solution appears straightforward. Most of the technologies and skills we need – renewable energy, energy efficiency, a new transmission line, railways, cycleways, urban design – are commercially available and affordable. In theory these could be scaled up rapidly.

But in practice there are several big, non-technical barriers. These include politics dominated by vested interests, culture, and institutions (organisational structures, laws, and regulations).

Vested interests include the fossil fuel industry, electricity sector, aluminium smelting, concrete, steel and motor vehicles. Governments that receive taxation revenue and political donations from vested interests are reluctant to act effectively.

To overcome this barrier, we need strong and growing pressure from the climate action movement.

There are numerous examples of nonviolent social change movements the climate movement can learn from. Examples include the Indian freedom struggle led by Gandhi; the African-American civil rights movement led by Martin Luther King Jr; the Philippine People Power Revolution; and the unsuccessful Burmese uprising of 1988-90.

Several authors, including Australian climate scientist Matthew England, point out that nations made rapid socio-economic changes during wartime and that such an approach could be relevant to rapid climate mitigation.

Learning from war

UNSW PhD candidate Laurence Delina has investigated the rapid, large, socio-economic changes made by several countries just before and during World War 2.

He found that we can learn from wartime experience in changing the labour force and finance.

However, he also pointed out the limitations of the wartime metaphor for rapid climate mitigation:

• Governments may need extraordinary emergency powers to implement rapid mitigation, but these are unlikely to be invoked unless there is support from a large majority of the electorate.

• While such support is almost guaranteed when a country is engaged in a defensive war, it seems unlikely for climate action in countries with powerful vested interests in greenhouse gas emissions.

• Vested interests and genuinely concerned people will exert pressure on governments to direct their policies and resources predominantly towards adaptation measures such as sea walls, and dangerous quick fixes such as geoengineering. While adaptation must not be neglected, mitigation, especially by transforming the energy sector, should be primary.

Unfortunately it’s much easier to make war than to address the global climate crisis rapidly and effectively. Indeed many governments of “democratic” countries, including Australia, make war without parliamentary approval.

Follow the leaders!

According to Climate Action Tracker, the 158 climate pledges submitted to the United Nations by December 8 2015 would result in around 2.7℃ of warming in 2100 – and that’s provided that all governments meet their pledge.

Nevertheless, inspiring case studies from individual countries, states and cities could lead the way to a better global outcome.

Iceland, with its huge hydroelectric and geothermal resources, already has 100% renewable electricity and 87% renewable heat.

Denmark, with no hydro, is on track to achieve its target of 100% renewable electricity and heat by 2035.

Germany, with modest hydro, is heading for at least 80% renewable electricity by 2050, but is behind with its renewable heat and transport programs.

It’s easier for small regions to reach 100% renewable electricity, provided that they trade electricity with their neighbours. The north German states of Mecklenburg-Vorpommern and Schleswig-Holstein are generating more than 100% net of their electricity from renewables.

The Australian Capital Territory is on track to achieve its 100% renewable electricity target by 2020. There are also many towns and cities on programs towards the 100% goal.

If the climate action movement can build its strength and influence, it may be possible for the state of Tasmania to achieve 100% renewable energy (electricity, heat and transport) and for South Australia to reach 100% renewable electricity, both within a decade.

But the eastern mainland states, which depend heavily on coal for electricity, will need to build new renewable energy manufacturing industries and to train a labour force that includes many more highly trained engineers, electricians, systems designers, IT specialists and plumbers, among others.

Changes will be needed to the National Electricity Market rules, or at least to rewrite the National Electricity Objective to highlight renewable energy, a slow task that must obtain the agreement of federal, state and territory governments.

Australia has the advantage of huge renewable energy resources, sufficient to create a substantial export industry, but the disadvantage of a declining manufacturing sector.

There are already substantial job opportunities in renewable energy, both globally and in Australia. These can be further expanded by manufacturing components of the technologies, especially those that are expensive to ship between continents, such as large wind turbine blades, bulk insulation and big mirrors.

Transport will take longer to transform than electricity generation and heat. Electric vehicle manufacturing is in the early stage of expansion and rail transport infrastructure cannot be built overnight, especially in car-dependent cities.

For air transport and long-distance road transport, the only short-term solution is biofuels, which have environmental and resource constraints.

How long would it take?

The timescale for the transition to 100% renewable energy – electricity, heat and transport – depends on each country or region and the commitment of its governments.

Scenario studies (see also here), while valuable for exploring technological strategies for change, are not predictions. Their results depend upon assumptions about the non-technical strategies I have discussed. They cannot predict the timing of changes.

Governments need to agree on a strategy for transitioning that focuses not just on the energy sector, but includes industry, technology, labour, financial institutions, governance and the community.

Everyone should be included in developing this process, apart from dyed-in-the-wool vested interests. This process could draw upon the strengths of the former Ecologically Sustainable Development process while avoiding its shortcomings.

The task is by no means easy. What we need is a strategic plan and to implement it rapidly.

Mark Diesendorf, Associate Professor, Interdisciplinary Environmental Studies, UNSW, UNSW Australia

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

Tigers: Help Save the Tiger

The link below is to an article reporting on the Tiger and its rapid slide to extinction. At the end of the article there is a link to a site where you can help save the tiger from extinction.

For more visit:
http://www.huffingtonpost.com/2012/05/06/tigers-pictures_n_1490131.html