Tag Archives: Greenland

Bluefin tuna follow prey to warming high Arctic

Large bluefin tuna that were caught among mackerel near Greenland Image: Greenland Fisheries License Control Authority
Large bluefin tuna that were caught among mackerel near Greenland
Image: Greenland Fisheries License Control Authority

By Alex Kirby

A research ship’s surprise catch of bluefin tuna further north than ever recorded indicates that climate change is restructuring the food web as the waters of east Greenland get warmer.

LONDON, 8 September, 2014 − Biologists and fishermen aboard a scientific cruise in the Arctic while they investigated mackerel stocks caught more than they bargained for − three large bluefin tuna, each weighing about 100 kilograms.

The research ship was sailing through the Denmark Strait, which separates Greenland from Iceland. Bluefin tuna are very seldom found near Greenland, and there are no other scientific reports of them venturing that far north. The most recent report of a tuna anywhere near was a stranding in 1900, a long way south at Qaqortoq, on the south-western tip of Greenland.

Details of the find, during a cruise in August 2012 organised by the Center for Macroecology, Evolution and Climate at the University of Copenhagen, have now been published in the journal Global Change Biology.

Expanded range

The lead author, Professor Brian MacKenzie, said bluefin tuna usually search for prey in areas where surface temperatures are warmer than 11°C.

At the time of the catch, the Denmark Strait was unusually warm, and one of tuna’s preferred prey species, mackerel, had already expanded their range into the region.

Professor MacKenzie and his colleagues write: “Regional temperatures in August 2012 were historically high and contributed to a warming trend since 1985, when temperatures began to rise.

“The presence of bluefin tuna in this region is likely due to a combination of warm temperatures . . . and immigration of an important prey species to the region. We conclude that a cascade of climate change impacts is restructuring the food web in east Greenland waters.”

They say their data was too limited to estimate how many tuna came so far north, but because bluefins are a schooling species − with schools having from 10 to 100 individuals − and because the three tuna were caught in the same haul, it is likely there were many more present.

The report says: “Satellite imagery showing the spread of warm water from the south-east towards east Greenland suggests that recent warming and climate change may have opened a migration pathway from the European shelf towards Greenland for migratory species.”

It acknowledges that the fish may have swum to the Denmark Strait from the north-west Atlantic, and concludes: “Our results show that rising temperatures have been progressively leading a . . . trophic [high in the food chain] cascade into east Greenland waters via improved thermal conditions for migratory prey and predator species.”

New fishing quotas

Nobody knows why bluefin tuna disappeared from the waters near Denmark and in the Norwegian Sea during the 1960s, nor when they might return. But Iceland and Norway have been allocated new fishing quotas of 30 tonnes each for the species in 2014.

An adult bluefin tuna is typically 1.5m-2m long, but some have been as big as 4.5m and weighed 650 kg. The fish are highly prized for sushi, especially in Japan.

Further climate-related changes in distributions of commercial fish such as mackerel and herring will mean new fishery and ecosystem management plans are going to be needed, says the report’s co-author, Helle Siegstad, head of the Department for Fish and Shellfish at the Greenland Institute of Natural Resources.

The Denmark Strait tuna will be discussed at the annual science conference of the International Council for the Exploration of the Sea (ICES), which starts on 15 September in the Spanish coastal city of A Coruña. – Climate News Network

Satellite mapping shows ice caps’ faster melt rate

Surface water flows into a 'moulin' shaft in Greenland's ice cap Image: NASA via Wikimedia Commons
Surface water flows down into a ‘moulin’ shaft in the Greenland ice cap
Image: NASA via Wikimedia Commons

By Tim Radford

Scientists have been able to measure more accurately than ever the thickness of the world’s major ice caps  revealing that melting is causing the loss of 500 cubic kms of ice annually.

LONDON, 1 September, 2014 − German researchers have established the height of the Greenland and Antarctic ice caps with greater precision than ever before. And the new maps they have produced show that the ice is melting at an unprecedented rate.

The maps, produced with a satellite-mounted instrument, have elevation accuracies to within a few metres. Since Greenland’s ice cap is more than 2,000 metres thick on average, and the Antarctic bedrock supports 61% of the planet’s fresh water, this means that scientists can make more accurate assessments of annual melting.

Dr Veit Helm and other glaciologists at the Alfred Wegener Institute’s Helmholtz Centre for Polar and Marine Research in Bremerhaven, Germany, report in the journal The Cryosphere that, between them, the two ice sheets are now losing ice at the unprecedented rate of 500 cubic kilometres a year.

Big picture

The measurements used to make the maps were taken by an instrument aboard the European Space Agency’s orbiting satellite CryoSat-2. The satellite gets closer to the poles − to 88° latitude − than any previous mission and traverses almost 16 million sq km of ice, adding an area of ice the size of Spain to the big picture of change and loss in the frozen world.

CryoSat-2’s radar altimeter transmitted 7.5 million measurements of Greenland and 61 million of Antarctica during 2012, enabling glaciologists to work with a set of consistent measurements from a single instrument.

Over a three-year period, the researchers collected 200 million measurements in Antarctica and more than 14 million in Greenland. They were able to study how the ice sheets changed by comparing the data with measurements made by NASA’s ICESat mission.

More complex

Greenland’s volume of ice is being reduced at the rate of 375 cubic km a year. In Antarctica, the picture is more complex as the West Antarctic ice sheet is losing ice rapidly, but is growing in volume in East Antarctica.

Overall, the southern continent − 98% of which is covered with ice and snow − is losing 125 cubic km a year. These are the highest rates observed since researchers started making satellite observations 20 years ago.

“Since 2009, the volume loss in Greenland has increased by a factor of about two, and the West Antarctic ice sheet by a factor of three,” said Angelika Humbert, one of the report’s authors. − Climate News Network

Underworld threat to melting icecap

 

Concealed beneath the Petermann glacier are towering blocks of ice Image: Michael Studinger/NASA via Wikimedia Commons
Concealed beneath the Petermann glacier are towering blocks of ice
Image: Michael Studinger/NASA via Wikimedia Commons

By Tim Radford

Radar images of Greenland’s glaciers have revealed a spectacular underground landscape of “skyscraper” ice blocks created by a melt-and-freeze cycle that is accelerating the reduction of the icecap

LONDON, 16 June − Researchers in the US have identified a new reason for the acceleration in the melting of Greenland’s icecap − the ice underneath, as it melts and then refreezes, appears to speed up glacial flow.

The melt-and-freeze-again cycle is not itself new, as a similar process has been diagnosed under the ice cap of Antarctica. Nor is the process itself necessarily connected with global warming. Such things must always have happened.

But Robin Bell, a geophysicist at Columbia University’s Lamont Doherty Earth Observatory, reports with colleagues in Nature Geoscience that they used ice-penetrating radar to identify ragged blocks of ice as tall as skyscrapers and as wide as the island of Manhattan at the very bottom of the ice sheet. These structures cover about a tenth of the island and seem to form as melted water below the ice freezes again. They then warp the ice around and above them.

Easier to flow

“We see more of these features where the ice sheet starts to go fast,” Professor Bell said. “We think the refreezing process uplifts, distorts and warms the ice above, making it softer and easier to flow.”

Bell and her colleagues looked at the Petermann Glacier in Greenland’s north, which in 2010 pushed a huge chunk of ice into the sea. Observations suggest that the glacier is moving twice as fast as the surrounding ice, and the hypothesis is that the melt-and-freeze-again process is contributing to this acceleration.

Researchers have been troubled for a decade or more by the apparent increase in ice loss from Greenland. Were the whole island to melt, sea levels worldwide would rise by more than seven metres, so the concern is practical.

Recently, researchers have found that the bedrock beneath many glaciers is actually below sea level, making the glaciers vulnerable from ocean inflow. They have identified a process called “dynamic thinning”, triggered by warmer air temperatures, and they know anyway that natural geothermal heat flow mis likely to melt the base of the ice and lubricate any acceleration.

They have measured a fourfold increase since 1997 in summer flow speeds in the island’s Jakobshavn glacier. And they have indicated that the Greenland icecap each summer becomes more vulnerable to melting because the snows themselves are becoming darker, as more dust blows in from areas that are increasingly ice free.

Ice slide

So the discovery of a process that will make the ice slide to the sea more efficiently is not of itself more sinister. The meltwater could come from a number of sources. The friction created by a glacier as it moves must contribute. So could natural heat flow from the bedrock. Surface ice could melt in the summer sun and drain through crevasses to the base.

However, what the discovery helps to offer, literally and metaphorically, is a deeper understanding of the processes at work below the ice.

What is not clear is whether the melt-and-freeze cycle will influence the rate at which ice is lost in future. Nor does anyone yet know what triggers the cycle.

“The conditions under which such switches occur should be investigated, as they directly affect the ability of an ice sheet to slide over its bed,” advises Joseph A. McGregor, of the University of Texas at Austin, writing in the same issue of Nature Geoscience. − Climate News Network

Dark shadow falls on melting icecap

 

Signs of melting as darkness falls on the Greenland icecap Image: Matthew Hoffmann/NASA ICE via Wikimedia Commons
Signs of melting can be seen as darkness descends on the Greenland icecap
Image: Matthew Hoffmann/NASA ICE via Wikimedia Commons

By Tim Radford

Dust blowing in from warming areas of the Arctic is causing the Greenland icecap to melt faster by reducing the whiteness that reflects light and keeps it cool 

LONDON, 13 June − French scientists have identified a new mechanism that could cause the Greenland icecap to melt even faster – because dust is making its surface darker.

Marie Dumont, of the French national meteorological service, Météo-France, reports with colleagues in Nature Geoscience that, since 2009, the snows of the Arctic region’s biggest single permanent white space have been steadily darkened by “light-absorbing impurities” − known to the rest of the world simply as dust.

The Arctic has always been cold and white, simply because it is not just cold but is also white. The phenomenon is called albedo. Regions with a high albedo reflect light and stay cooler, so ice is a form of self-insulation.

Conversely, things that absorb light become warmer − and satellite data analysed by Dr Dumont and her fellow researchers shows that the Greenland ice is getting darker in the springtime.

They think the dust is blowing in from areas of the Arctic that are losing snow cover much earlier in the season as the climate warms. And, they calculate, this steady darkening alone has led to “significant” melting of the icecap.

This finding is ominous. What the researchers have identified is yet another case of what engineers call positive feedback. In the last 30 years, the Arctic sea ice has been in retreat, and researchers expect that, later in the century, the Arctic ocean will be entirely free of ice most summers.

Insulating layers

That means that there will be more atmospheric dust each spring, landing on the snows of Greenland and lowering its albedo even more, so the insulating layers of ice on the huge island will continue to retreat.

Researchers have twice in the last few months had to revise their predictions for the melting of the Greenland glaciers. The continued melting of the ice sheet is expected to raise global sea levels by 20cm by 2100, and since the whole ice sheet – which would take much longer to melt − holds enough frozen water to raise sea levels by more than seven metres, what happens in Greenland matters very much to maritime cities as far apart as Miami and Mumbai.

The French researchers have backed up their observations with a computer model of potential surface melt in Greenland. If a perfect reflecting surface would have a value of one, then meteorologists allot a value of 0.9 to the albedo of fresh snow. They calculate that a decrease in the albedo of even a very small ratio, such as 0.01, could lead to the melting of 27 billion tons of ice every year.

They are not saying that this is already happening, but they do argue that “future trends in light-absorbing impurities should therefore be considered in projections of Greenland’s mass loss”.

Accelerating warming

This is not the only newly-identified potential mechanism for positive feedback. A report by Laetitia Pichevin, of the University of Edinburgh’s School of GeoSciences, Scotland, and fellow researchers, was published in the same issue of Nature Geoscience. It says that rising global temperatures could decrease the amount of carbon dioxide naturally taken up by the world’s oceans, thus also accelerating global warming. This, too, is another process that could go on accelerating.

The researchers analysed sediments laid down 26,000 years ago in the Gulf of California and measured the abundance of silicon and iron in tiny marine fossils. They found that those periods when silicon was least abundant in ocean waters coincide with relatively warmer climates, low levels of atmospheric iron, and reduced carbon dioxide uptake by the plankton in the oceans.

“We were surprised by the many ways in which iron affects the CO2 given off by the oceans,” Dr Pichevin said. “If warming climates lower iron levels at the sea surface, as occurred in the past, this is bad news for the environment.” – Climate News Network

How nature affects the carbon cycle

FOR IMMEDIATE RELEASE

By Tim Radford

In Australia and the Arctic, scientists say, they have found unexpected ways in which natural processes are helping to compensate for global warming.

LONDON, 1 June – The great drylands of the planet – and they cover almost half of the terrestrial surface – may be bigger players in the carbon cycle than anyone had suspected. The world’s semi-arid regions may absorb huge volumes of carbon dioxide from the atmosphere whenever it rains enough.

A greening semi-arid ecosystem in Australia's Northern Territory, a key factor the record 2011 global land carbon sink following prolonged La Niña rainfall and long-term vegetation changes  
Image: Eva van Gorsel (CSIRO)

A greening semi-arid ecosystem in Australia’s Northern Territory, a key factor in the record 2011 global land carbon sink following prolonged La Niña rainfall and long-term vegetation changes

Image: Eva van Gorsel (CSIRO)

Benjamin Poulter of Montana State University and colleagues report in Nature that they used a mix of computer-driven accounting methods to work out where the carbon goes after fossil fuel burning emits extra carbon dioxide into the atmosphere. Decades of meticulous measurement confirm that, overall, carbon dioxide levels are increasing inexorably, and the world is warming accordingly.

But inside this big picture is a lot of seasonal and inter-annual variation. So climate scientists, when they try to work out what all this means for future climates, need to understand the carbon cycle better.

The assumption has always been that the most important terrestrial consumers of carbon dioxide were the tropical rainforests. But the match of terrestrial biogeochemical and atmospheric carbon dioxide and global carbon budget accounting models by 13 scientists from the US, Europe and Australia has revealed a different story.

In 2011 more than half of the terrestrial world’s carbon uptake was in the southern hemisphere – which is unexpected because most of the planet’s land surface is in the northern hemisphere – and 60% of this was in Australia.

Natural brake

That is, after a procession of unusually rainy years, and catastrophic flooding, the vegetation burst forth and the normally empty arid centre of Australia bloomed. Vegetation cover expanded by 6%.

Human activity now puts 10 billion tonnes of carbon into the atmosphere annually, and vegetation in 2011 mopped up 4.1 billion tonnes of that, mostly in Australia.

There remains a great deal of uncertainty about the carbon cycle and how the soils and the trees manage the extra carbon. Nobody knows what will happen to this extra carbon now in the hot dry landscapes of Australia: will it be tucked away in the soil? Will it be returned to the atmosphere by subsequent bushfires? As scientists are fond of saying, more research is necessary.

But this is an example of negative feedback: as carbon dioxide levels and temperatures rise, the green things respond, and slow the acceleration of both. This is quite different from the positive feedback that follows when Arctic ice – which reflects sunlight – melts and gives way to blue water which absorbs solar energy, thus accelerating the melting.

But even the slow disaster of the polar regions could be accompanied by an ameliorating process. British researchers report in Nature Communications that the ice sheet meltwaters may be rich in iron. A boost of iron would stimulate phytoplankton growth, which means more carbon dioxide could accordingly be absorbed from the atmosphere.

Feeding the oceans

The scientists collected meltwater from a Greenland glacier in the summer of 2012, and then tested it to discover significant quantities of what geochemists call “bio-available” iron.

So, in another example of those cycles of the elements that make the world go round, ice that scrapes over rock also delivers vital nutrients to the sea, for marine plants to take up yet more carbon dioxide and flourish more vigorously in the oceans and keep the planet a little cooler.

The Greenland research gives scientists a chance to estimate more accurately the delivery of this dietary supplement to the oceans: they reckon somewhere between 400,000 and 2.5 million tonnes a year in Greenland and somewhere between 60,000 and 100,000 tonnes in Antarctica. Or, to put it more graphically, it would be like dropping 3,000 fully-laden Boeing 747s into the ocean each year.

“The Greenland and Antarctic ice sheets cover around 10% of the global land surface,” said Jon Hawkings, of the University of Bristol, UK. “Our finding that there is also significant iron discharged in runoff from large ice sheet catchments is new. This means that relatively high concentrations are released from the ice sheet all summer, providing a continuous source of iron to the coastal ocean.” – Climate News Network

Greenland ice may melt even faster

FOR IMMEDIATE RELEASE

 

Danger zone: Aerial view of the margin of Greenland's ice sheet Image: Hannes Grobe/Alfred Wegener Institute via Wikimedia Commons

Melting away: an aerial view of the margin of Greenland’s threatened ice sheet
Image: Hannes Grobe/Alfred Wegener Institute via Wikimedia Commons

By Tim Radford

Research scientists discover that the vulnerability of Greenland’s glaciers to global warming is much greater than feared, increasing the threat of rising sea levels around the globe 

LONDON, 24 May − Just days after US researchers identified geophysical reasons why West Antarctica’s glaciers are increasingly vulnerable to global warming, a partner team has pinpointed a related cause for alarm in Greenland.

Many of the bedrock crevices and canyons down which the island’s glaciers flow have basements that are below sea level. This means that as warm Atlantic waters hit the glacier fronts, the glaciers themselves become more vulnerable to global warming and increasingly likely to melt at a faster rate.

Researchers have been worried for years about rates of melting in Greenland, which is why scientific attention to the vast, ancient ice cap has been stepped up. But the latest finding suggests that what had seemed bad news could turn out to be much, much worse.

If accelerated melting does happen – and all such predictions will be tested initially by yet more research, and then ultimately by time itself – it will be the consequence of an unholy mix of man-made global warming and entirely accidental geomorphology.

The presumption is that terrestrial landforms are routinely above the sea’s highest tides. But Mathieu Morlighem, of the University of California, Irvine, and colleagues – one of whom is Eric Rignot, who authored the research on West Antarctic glaciers, reported in Nature Geoscience − found that this is not always the case.

Radar soundings

They used airborne radar soundings and satellite data to show that beneath the glacial ice were valleys so deeply incised that some of them were hundreds of metres below sea level, at distances tens of kilometres from the sea.

The researchers conclude: “Our findings imply that the outlet glaciers of Greenland, and the ice sheet as a whole, are probably more vulnerable to ocean thermal forcing and peripheral thinning than inferred previously from existing numerical ice sheet models.”

The scientists, of course, could not see these new, deep slashes in the bedrock − they lie under a huge burden of locked or very slowly moving ice. To arrive at their conclusions they had to combine the satellite and radar data, and estimates of snowfall and ice melt, to build up a “mass conservation algorithm” that could reveal the secrets of the buried bedrock.

“This has major implications, because the glacier melt
will contribute much more to rising seas around the globe”

“The glaciers of Greenland are likely to retreat faster and further inland than anticipated – and for much longer – according to this very different topography we’ve discovered beneath the ice,” Morlighem said. “This has major implications, because the glacier melt will contribute much more to rising seas around the globe.”

But even before the warming seas start to lap at the rim of Greenland’s icy mountains and melt the glaciers from beneath, global warming threatens the icecaps from above. Kaitlin Keegan, of Dartmouth College in the US, and colleagues report in the Proceedings of the National Academy of Sciences that the dramatic surface melting of the island’s ice sheet in 2012 can be explained by a combination of unprecedented temperatures linked to climate change and clouds of ash and soot from forest fires.

And since climate change is on the way and forest fires are on the increase, the process will go on, and Greenland’s icy surface will melt more often in the northern summers. By 2100, practically the whole of the Greenland ice sheet will be subject to widespread annual meltdown.

Freak weather

In July 2012, more than 97% of the Greenland ice sheet melted at the surface. This was seen as an event blamed on freak weather conditions, or perhaps as an indicator of things to come.

Forest fires were a feature of that long, hot North America summer, but their effect was more difficult to measure. Now it seems that clouds of black carbon reduced the albedo – that is, the ability of snow and ice to reflect sunshine back into space and keep itself cold. At the same time,  the warmer air of summer pushed the ground temperatures above freezing point.

The team looked at the evidence of ice cores and found signs of similar dramatic melting in 1889. They also found scatters of forest fire ash in the layers from 1868 and 1908, but the summers of these years were too cold to permit any melting of the ice sheet.

“With both the frequency of forest fires and warmer temperatures predicted to increase with climate change, widespread melt events are likely to happen much more frequently in the future,” Keegan says.  – Climate News Network

No way back for West Antarctic glaciers

FOR IMMEDIATE RELEASE

 

Birth of an iceberg: a massive crack appears in the Pine Island glacier in West Antarctica Image: Nasa Earth Observatory via Wikimedia Commons

Birth of an iceberg: a massive crack in West Antarctica’s Pine Island glacier
Image: Nasa Earth Observatory via Wikimedia Commons

By Tim Radford

Satellite data analysis reveals the ominous news that the melting glaciers of West Antarctica have passed the ‘point of no return’ as the southern hemisphere gets warmer

LONDON, 22 May – The glaciers of the West Antarctic may be in irreversible retreat, according to the evidence of satellite data analysed by scientists at the US space agency Nasa.

The study of 19 years of data, due to be reported in the journal Geophysical Research Letters, confirms the ominous news that the southern hemisphere is not just warming − it is that it is warming in a way that speeds up the melting of the West Antarctic glaciers.

Long ago, glaciologists began to wonder whether the West Antarctic ice sheet was inherently unstable. The water locked in the ice sheet in the Amundsen Sea region – the area the Nasa researchers examined − is enough to raise global sea levels by more than a metre. If the whole West Antarctic ice sheet turned to water, sea levels would rise by at least five metres.

Steady change

What the latest research has revealed is a steady change in the glacial grounding line, which is the point in a glacier’s progress towards the sea where its bottom no longer scrapes on rock but starts to float on water. It is in the nature of a glacier to flow towards the sea, and at intervals to calve an iceberg that will then float away and melt. The puzzle for scientists has been to work out whether this process has begun to accelerate.

Eric Rignot, a glaciologist at the Nasa Jet Propulsion Laboratory and the University of California, Irvine, thinks it has. He and his research partners believe that European Space Agency satellite data has recorded the points at which the grounding lines can be identified in a series of West Antarctic glaciers monitored between 1992 and 2011, as the glaciers flexed in response to the movement of tides.

All the grounding lines had retreated upstream, away from the sea − some by more than 30 kilometres. The grounding lines are all buried under hundreds of metres of ice, and are difficult to identify.

The shift of ice in response to tidal ebb and flow provides an important clue. It also signals an acceleration of melting, because it is the glacier’s slowness that keeps the sea levels static. As it inches towards the sea, there is time for more snow and ice to pile up behind it.

Speeds up

But if the water gets under the ice sheet, it reduces friction and accelerates the passage of frozen water downstream. So the whole glacier speeds up, and the grounding line moves yet further upstream.

Something similar has been reported from the glaciers of Greenland. And once the process starts, there is no obvious reason why it would stop. The melting will still be slow, but the latest evidence indicates that it seems to be inexorable.

“We’ve passed the point of no return,” Prof Rignot says. “At current melt rates, these glaciers will be history within a few hundred years.

“The collapse of this sector of West Antarctica appears to be unstoppable. The fact that the retreat is happening simultaneously over a large sector suggests it was triggered by a common cause, such as an increase in the amount of ocean heat beneath the floating sections of the glaciers. At this point, the end of this sector appears to be inevitable.” – Climate News Network

Glacier tracing goes digital

FOR IMMEDIATE RELEASE

 

The Aletsch glacier, Switzerland, a country where the health of glaciers is vital for tourism  IMAGE: Didier Baertschiger via Wikimedia Commons

The Aletsch glacier in Switzerland, where the health of glaciers is vital for tourism
Image: Didier Baertschiger via Wikimedia Commons

By Paul Brown

Detailed new maps of all the world’s glaciers have been produced to provide vital data that will help plan for the effects of climate change

LONDON, May 10 – Scientists have for the first time compiled a complete map of all the glaciers on Earth, providing extensive data that will help calculate sea level rise caused by global warming and the threats to communities that rely on melt water for agriculture and water supply.

The data, including length and volume, is contained in a collection of digital outlines of the world’s 200,000 glaciers − excluding the Greenland and Antarctica ice sheets.

It has been named the Randolph Glacier Inventory, after the US town of Richmond, New Hampshire, which was one of the meeting places for the group of international scientists who carried out the study as part of the fifth assessment report of the Intergovernmental Panel on Climate Change (IPCC). The study has been published in the Journal of Glaciology.

Many glaciers are in extremely remote regions, such as the Himalayas and Greenland, which has made them hard to reach − let alone measure their length and thickness. A combination of large-scale efforts by volunteers on the ground and satellite technology has overcome these difficulties, enabling 70 scientists from 18 countries to compile the maps.

Overall, the glaciers cover 730,000 square km − an area the size of Germany, Poland and Switzerland combined. The volume of ice is about 170,000 cubic km, which is less than previously thought, but still enough to raise global sea levels between 35cm and 47cm if they all melted.

Sea level rise

Although this is less than 1% of the amount of water stored in the Greenland and Antarctica icecaps, it matters because most of the glaciers are melting now, actively adding to sea level rise. The two big icecaps are so cold inside that it will be thousands of years before the ice temperature rises enough to reach melting point.

Some of the most populous areas on earth, such as China, India and Pakistan, rely on melt water from glaciers for agriculture. At present, glaciers still provide plenty of summer water, but in many cases they are melting faster than winter snows are replenishing them. If this continues, the summer water flow will eventually cease, leading to calamity for the human populations that rely on them.

This is already happening in some parts of the Andes in South America, with some smaller glaciers having disappeared. The impact affects, for example, some wine-growing regions that rely on melt water for their vines.

There are still uncertainties about some of the measurements because, in some cases, glaciers are covered in debris as they move down mountains, while others are obscured by snow, making measurements of thickness more difficult.

Each glacier in the new inventory is represented by a computer-readable outline, making precise modelling of glacier-climate interactions much easier.

Glaciers currently add about one-third to existing sea level rise − about the same amount as the two giant ice sheets. The remaining third is the result of thermal expansion of the oceans as they warm.

Speed of retreat

In countries such as Switzerland, where the health of glaciers is vital for tourism, the speed of their retreat has been closely monitored. The melting is also important because it causes landslides, as well as impacting on water supply.

“The rapid shrinking of glaciers during the past 20 years is well recognisable in the Alps and other parts of the world,” said Frank Paul, a senior researcher in the University of Zurich’s Department of Geography and a co-author of the study.

Tobias Bolch, a researcher at the Institute for Cartography at the Technische Universität Dresden, Germany, is another co-author of the study. He said: “Here and in other parts of the world glaciers also impact on the regional to local-scale hydrology, natural hazards, and livelihoods in otherwise dry mountain regions.

“Accurate knowledge of water reserves and their future evolution is thus key for local authorities for early implementation of mitigation measures.” – Climate News Network

Greenland’s icecap loses stability

FOR IMMEDIATE RELEASE

The calving front of the Jakobshaven Glacier in western Greenland in April 2012 Image: NASA ICE via Wikimedia Commons

The calving front of the Jakobshaven Glacier in western Greenland in April 2012
Image: NASA ICE via Wikimedia Commons

By Tim Radford

Greenland is losing ice from part of its territory at an accelerating rate, suggesting that the edges of the entire ice cap may be unstable.

LONDON, 13 April – Greenland – the largest terrestrial mass of ice in the northern hemisphere – may be melting a little faster than anyone had guessed.

A region of the Greenland ice sheet that had been thought to be stable is undergoing what glaciologists call “dynamic thinning”. That is because the meltwater from the ice sheet is getting into the sea, according to a study in Nature Climate Change.

In short, Greenland’s contribution to sea level rise has been under-estimated, and oceanographers may need to think again about their projections.

Shfaqat Khan from the Technical University of Denmark and colleagues used more than 30 years of surface elevation measurements of the entire ice sheet to discover that overall loss is accelerating. Previous studies had identified melting of glaciers in the island’s south-east and north-west, but the assumption had been that the ice sheet to the north-east was stable.

Four times as fast

It was stable, at least until about 2003. Then higher air temperatures set up the process of so-called dynamic thinning. Ice sheets melt every Arctic summer, under the impact of extended sunshine, but the slush on the glaciers tends to freeze again with the return of the cold and the dark, and since under historic conditions glaciers move at the proverbial glacial pace, the loss of ice is normally very slow.

But global warming, triggered by rising levels of greenhouse gases in the atmosphere, has changed all that. Greenland’s southerly glaciers have been in retreat and one of them, Jakobshavn Isbrae, is now flowing four times faster than it did in 1997.
Now the Danish-led team has examined changes linked to the 600 kilometre-long Zachariae ice stream in the north-east.

This has retreated by about 20 kms in the last decade, whereas Jakobshavn has retreated about 35 kms in 150 years. The Zachariae stream drains around one-sixth of the Greenland ice sheet, and because warmer summers have meant significantly less sea ice in recent years, icebergs have more easily broken off and floated away, which means that the ice stream can move faster. The researchers used satellite studies to measure ice loss.

“North-east Greenland is very cold. It used to be considered the last stable part of the Greenland ice sheet,” said one of the team, Michael Bevis of Ohio State University in the US.

Deep impacts

“This study shows that ice loss in the north-east is now accelerating. So now it seems that all of the margins of the Greenland ice sheet are unstable.”

The scientists used a GPS network to calculate the loss of ice. Glacial ice presses down on the bedrock below it: when the ice melts, the bedrock rises in response to the drop in pressure, and sophisticated satellite measurements can deliver enough information to help scientists put a figure on the loss of ice.

They calculate that between April 2003 and April 2012, the region was losing ice at the rate of 10 billion tons a year.

“This implies that changes at the margin can affect the mass balance deep in the centre of the ice sheet,” said Dr Khan. Sea levels are creeping up at the rate of 3.2 mm a year. Until now, Greenland had been thought to contribute about half a mm. The real figure may be significantly higher. – Climate News Network

Greenland’s fastest glacier picks up pace

FOR IMMEDIATE RELEASE

An iceberg calved from the rapidly accelerating Jakobshavn Isbræ floats in Greenland's Disko Bay Image: Courtesy of Ian Joughin, PSC/APL/UW

An iceberg calved from the rapidly accelerating Jakobshavn Isbræ floats in Greenland’s Disko Bay
Image: Courtesy of Ian Joughin, PSC/APL/UW

By Tim Radford

Research from the Arctic shows Greenland’s fastest-flowing glacier has doubled its summer flow pace in a decade, and ice cover on Alaskan lakes is declining.

LONDON, 6 February – A fast-moving Arctic glacier which has earned a place in history is now accelerating even more quickly. The Jakobshavn Isbrae (the Danish word for glacier) is a massive river of ice from the Greenland ice sheet to an Atlantic ocean fjord and is thought – there is no way of proving this – to be the source of the giant iceberg that sank the Titanic in 1912.

According to research published in the European Geosciences Union journal The Cryosphere, summer flow speeds have doubled yet again since a Nasa measurement in 2003. And that in turn represented a doubling of flow speeds since 1997.

The Jakobshavn glacier is Greenland’s fastest-flowing glacier. It now moves at 17 kilometres a year. That works out at 46 metres a day. With accelerations like this, phrases like “glacial pace” may no longer serve as clichés of lethargic movement. These speeds are recorded in the summer, when all glaciers are more likely to be a bit friskier. But even when averaged over the whole year, the glacier’s flow has accelerated threefold since the 1990s.

Icebergs “calve” from glaciers – they break off and drift out to sea. The Arctic ice sheet is thinning, and most of the planet’s glaciers are retreating as climates warm, so the Jakobshavn glacier is carrying less ice, at a faster rate, over shorter distances than ever before, and by the end of the century could have shifted 50 kilometres upstream. But right now it is also contributing to sea level rise at a faster rate.

“We know that from 2000 to 2010 this glacier alone increased sea level by about 1mm”, said Ian Joughin, of the Polar Science Centre at the University of Washington, who led the research. “With the additional speed it will likely contribute a bit more than this over the next decade.”

The scientists used satellite data to measure the rate of summer change in Greenland. But other satellite radar imagery has begun to reveal an ominous picture of change elsewhere in the Arctic, on the north slope of Alaska. Even during the winter months, ice on the lakes of Alaska has begun to decline. Warmer climate conditions means thinner cover on shallow lakes and a smaller fraction that freeze entirely during the winter months.

“We were stunned to observe such a dramatic ice decline during a period of only 20 years”

Cristina Surdu of the University of Waterloo in Canada and colleagues report in The Cryosphere that there has been a 22% fall in grounded ice – frozen from surface to lakebed – between 1991 and 2011.

They expected to find a decline in ice thickness when they embarked on a study of radar observations of 402 lakes near Barrow in Alaska from the European earth resources satellites ERS-1 and ERS-2. That was because they already had temperature and precipitation records from Barrow dating back five decades.

Freeze dates in the region are now occurring on average six days later than in the past, and the ice is breaking up on average around 18 days earlier.

“At the end of the analysis, when looking at trend analysis results, we were stunned to observe such a dramatic ice decline during a period of only 20 years”, Surdu said. – Climate News Network