Arctic glacier’s galloping melt baffles scientists

Arctic glacier’s galloping melt baffles scientists

New satellite data analysis has produced evidence that rapid melting in the last three years has caused dramatic shrinkage of an Arctic ice cap.

LONDON, 31 January, 2015 – An ice cap in the high Arctic has lost what British scientists say is a significant amount of ice in an unusually short time.

It has thinned by more than 50 metres since 2012 – about one sixth of its original thickness – and the ice flow is now 25 times faster, accelerating to speeds of several kilometres per year.

Over the last two decades, thinning of the Austfonna ice cap in the Svalbard archipelago − , roughly half way between Norway and the North Pole − has spread more than 50km inland, to within 10km of the summit. .

A team led by the scientists from the UK Centre for Polar Observation and Modelling (CPOM) at the University of Leeds combined observations from eight satellite missions, including Sentinel-1A and CryoSat, with results from regional climate models, to understand what was happening.

Sea level rise

The study’s lead author, geophysicist Dr Mal McMillan, a member of the CPOM team, said: “These results provide a clear example of just how quickly ice caps can evolve, and highlight the challenges associated with making projections of their future contribution to sea level rise.”

The study, published in Geophysical Research Letters, is the first to make use of measurements from the European Space Agency’s latest Earth observation satellite, Sentinel-1A.

Dr McMillan said: “New satellites, such as the Sentinel-1A and CryoSat missions, are essential for enabling us to systematically monitor ice caps and ice sheets, and to better understand these remote polar environments.”

“Whether or not the warmer ocean water
and ice cap behaviour are directly linked
remains an unanswered question”

Melting ice caps and glaciers account for about a third of recent global sea level rise. Although scientists predict that they will continue to lose ice in the future, determining the exact amount is difficult, because of a lack of observations and the complex nature of how they interact with the climate around them.

The 20 years of satellite data that the scientists have amassed show some fairly small changes at the start of the study period, but these have since increased.

“Glacier surges, similar to what we have observed, are a well-known phenomenon”, said Professor Andrew Shepherd, the director of CPOM. “What we see here is unusual because it has developed over such a long period of time, and appears to have started when ice began to thin and accelerate at the coast.”

There is evidence that the surrounding ocean temperature has increased in recent years, which may have been the original trigger for the ice cap thinning.

Flow models

Prof Shepherd said: “Whether or not the warmer ocean water and ice cap behaviour are directly linked remains an unanswered question. Feeding the results into existing ice flow models may help us to shed light on the cause, and also improve predictions of global ice loss and sea level rise in the future.”

The team says long-term observations by satellites are the key to monitoring such climate-related phenomena.

Dr McMillan told Climate News Network he did not think what was happening in Austfonna suggested any sort of tipping point in the Arctic, which scientists say is warming more than twice as fast as anywhere else on Earth.

He said: “What I take from this work is that we don’t understand well enough what’s caused this sort of behaviour − natural variability, ocean temperatures or atmospheric temperatures. It reinforces the complexities and the challenges of the future.” – Climate News Network

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Increased carbon spill from glaciers sets new puzzle

Increased carbon spill from glaciers sets new puzzle

Samples taken from five continents indicate that a big rise in organic carbon released by melting glaciers could have serious implications for ecosystems.

LONDON, 28 January, 2015 − Researchers in the US have calculated that, thanks to climate change, melting glaciers will have spilled an extra 15 million tonnes of organic carbon into the seas by 2050.

The consequences for the ecosystems that depend on glacial meltwater are uncertain, but this burden of biological soot and sediment has potential implications for the global carbon cycle as well.

The researchers estimate that the dissolved organic carbon released by melting glaciers will be an increase of half as much again on the current flow − the equivalent of about half the annual flow of dissolved carbon down the mighty Amazon River. And their calculations have identified another puzzle for climate scientists trying to understand the carbon cycle.

The planet’s glaciers and ice sheets cover about 11% of the planet’s surface and hold about 70% of the world’s fresh water. Spread thinly through this frozen water is a significant amount of biological carbon, with the Antarctic ice sheet alone hosting 6 billion tonnes of it.

Increased meltwater

It is safe for the time being, but mountain glaciers almost everywhere in the world are in retreat, and meltwater flow from the glaciers that drain the Greenland icecap is on the increase.

Eran Hood, professor of environmental science at the University of Alaska Southeast in Juneau, and colleagues report in Nature Geoscience that they developed a database of dissolved organic carbon found in 300 samples collected from glaciers on five continents.

Some of it was clearly preserved from living things on the ice itself, some of was scraped up as the glaciers moved over old soils, and some of it was soot from fossil fuel combustion or distant forest fires.

There was a wide spread of carbon concentrations in the samples, but it was enough to estimate a global average.

“We know we are losing glaciers, but what does that mean for marine life, fisheries, things downstream
that we care about?”

They also knew that Greenland and Antarctic icebergs delivered 4,250 billion tonnes of water to the oceans each year, and that the run-off from retreating mountain glaciers was somewhere between 369-905 billion tonnes.

So they could begin to make an estimate of the rate at which dissolved organic carbon is re-entering the planetary system, and perhaps augmenting the carbon cycle.

The carbon cycle underwrites all life: plants and microbes withdraw carbon from the atmosphere and some of it gets stored in the soilspreserved as peat, or locked away as rock, or frozen as ice to be returned to the planetary system in all sorts of ways,

New questions

Research like this is basic: it adds another detail or two to an understanding of how the planet works. It starts to answer existing questions − but it also raises new ones.

“This research makes it clear that glaciers represent a substantial reservoir of organic carbon,” said Dr Hood. “As a result, the loss of glacier mass worldwide, along with the corresponding release of carbon, will affect high latitude marine ecosystems, particularly those surrounding the major ice sheets that now receive fairly limited land-to-ocean fluxes of carbon.”

His co-author Robert Spencer, assistant professor of oceanography at Florida State University, said: “The thing people have to think about is what this means for the Earth. We know we are losing glaciers, but what does that mean for marine life, fisheries, things downstream that we care about?” – Climate News Network

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Scientists say rise in sea levels is faster than feared

Scientists say rise in sea levels is faster than feared

Harvard researchers find that there has been an almost threefold annual increase in global sea levels over the last quarter of a century.

LONDON, 22 January, 2015 − Sea level rise for most of the 20th century may have been over-estimated by as much as 30%. But the less welcome news is that, if that’s the case, then sea levels since 1990 have started to accelerate more sharply than anyone had ever expected.

Scientists at Harvard University, in the US, report in the journal Nature that they came to the conclusions after deciding that old data needed fresh analysis − using sophisticated mathematical filtering techniques for handling the uncertainties and gaps in such data.

Estimating and accounting for global mean sea level (GMSL) rise is critical to characterising current and future human-induced changes. The catch is that sea level measurement hasn’t been going on for very long, so not all measurement techniques have been the same. In addition, reliable, systematic and sustained sets of data are relatively sparse.

Rise and fall

The term “sea level” sounds pretty basic, but the oceans are hardly ever level. Tides swell and ebb, regions of sea rise and fall according to temperature and salinity, and the shorelines at which researchers take measurements can also go up because of tectonic movement or sink because of the abstraction of groundwater.

Measurements along some of the world’s great estuary systems can be skewed because of human interference over the decades with the flow downstream, and great tracts of ocean cannot be measured directly at all.

The challenge, then, is to arrive at an average sea level rise for the whole planet.

“We know that sea level is changing for a variety of reasons,” said Dr Carling Hay, post-doctoral fellow in Harvard’s Department of Earth and Planetary Sciences (EPS).

“There are ongoing effects due to the last ice age, heating and expansion of the ocean due to global warming, changes in ocean circulation, and present day melting of land-ice − all of which result in unique patterns of sea level change. These processes combine to produce the observed global mean sea level rise.”

So the Harvard scientists, working with colleagues from Rutgers University in New Jersey, made estimates for the meltwater from glaciers and dwindling ice caps, from ocean thermal expansion and factors. They then “smoothed” the data, using a mathematical modelling algorithm.

Earlier estimates put mean sea level rise in the 20th century at between 1.5 and 1.8 millimetres a year. Dr Hay and her colleagues now think that, between 1901 and 1990, the true figure was probably closer to 1.2mm a year.

But since 1990, global sea level has risen by 3mm a year on average. So, in fact, the acceleration since then has been faster than anybody expected – and this in turn could affect future projections.

Question of accuracy

“Another concern with this is that many efforts to project sea level change into the future use estimates of sea level rise over the time period from 1900 to 1990,” said co-author Eric Morrow, a recent Ph.D graduate of Harvard’s EPS

“If we’ve been over-estimating the sea level change during that period, it means that these models are not calibrated appropriately, and that calls into question the accuracy of projections out to the end of the century.”

Dr Hay added: “We expected that we would estimate the individual contributions, and that their sum would get us back to the 1.5 to 1.8mm a year that other people had predicted. But the math doesn’t work out that way.

“Unfortunately, our new lower rate of sea level rise prior to 1990 means that sea level acceleration that resulted in higher rates over the last 20 years is really much larger than anyone thought.” – Climate News Network

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Science gains from clearer sight of Greenland’s ice melt

Science gains from clearer sight of Greenland's ice melt

Research into how Greenland’s ice melts should lead to more accurate predictions of sea level rise and global warming.

LONDON, 18 January, 2015 − Scientists in the US have used on-the-ice measurements and military-grade satellite imagery to take a much closer look at just how Greenland’s icesheet melts.

They already knew that huge icebergs fall from the glaciers into the ocean, and that surface lakes drain suddenly in the summer warmth. But now they know considerably more about what happens to the network of streams, rivers and ponds that collect in the summer sunshine, and then flow across the top of the icesheet into moulins, or sinkholes.

They report in the Proceedings of the National Academy of Sciences that they used the data collected to chart 523 streams in a catchment area of about 6,800 square kilometres during the freak thaw of 2012, when almost the whole of the Greenland icecap was covered in slush. They measured the run-off at between 1,550 and 1,700 cubic metres per second − twice the average flow of the Colorado River.

Thereafter, all this water drained into moulins, and began to filter towards the base of the icesheet. What happened to it then is not yet certain, but the guess is that a percentage was soaked up within the iceshelf, while a proportion reached the sea.

Only the start

The study placed 11 researchers on the ice for six days in July 2012, during a massive and unusual melt. Only on one other occasion in the last 700 years, in 1889, did Greenland’s ice melt on such a scale.

The scientists were moved around by helicopter and equipped with a specially-designed automaton boat, buoys fitted with GPS technology, and sophisticated satellite imagery.

“It was a real preview of just how quickly that ice sheet can melt and the meltwater can escape”, said lead author Laurence Smith, Professor of Earth, Planetary, and Space Sciences at University of California Los Angeles. “The question was whether the ice sheet acts like a sponge or like Swiss cheese.”

The provisional answer is: both. Some meltwater stays, and some certainly escapes altogether. But it will take more than just one visit to arrive at more precise calculations.

“Greenland is really the big player for sea level rise in the future, so improving climate models is extremely crucial”

The scientists also took measurements of Greenland’s Isortoq river − just one of about 100 large terrestrial rivers delivering Greenland meltwater to the oceans.

They found that the Isortoq carries water from the ice sheet to the ocean at between 650 and 1,300 cubic metres per second, which is less than models have projected.

Such direct measurements are important because they make predictions of melt rate and sea level rise more accurate − and more credible.

“If we can get better estimates, then we can have better projections for the extent and impact of global warming”, said another of the report’s authors, Marco Tedesco, founder and director of the City College of New York’s Cryospheric Processes Laboratory. “Greenland is really the big player for sea level rise in the future, so improving climate models is extremely crucial.” – Climate News Network

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Ocean warming speeds up cycle of climate change

Ocean warming speeds up cycle of climate change

British and German scientists have identified another consequence of global warming that is likely to accelerate climate change still further.

LONDON, 9 January, 2015 − The warming oceans could start to return more carbon dioxide to the atmosphere as the planet warms, according to new research.

And since 70% of the planet is covered by clear blue water, anything that reduces the oceans’ capacity to soak up and sequester carbon could only make climate change more certain and more swift.

It is a process that engineers call “positive feedback”. And under such a cycle of feedback, the world will continue to get even warmer, accelerating the process yet again.

Many such studies are, in essence, computer simulations. But Chris Marsay − a marine biochemist at the UK’s National Oceanography Centre in Southampton − and colleagues based their results on experiments at sea.

Sediment traps

They report in the Proceedings of the National Academy of Sciences that they examined sediment traps in the North Atlantic to work out what happens to organic carbon – the tissue of the living things that exploit photosynthesis, directly or indirectly, to convert carbon dioxide – as it sinks to the depths.

Sooner or later, much of this stuff gets released into the sea water as carbon dioxide. This is sometimes called the ocean’s biological carbon pump. In deep, cold waters, the process is slow. In warmer, shallower waters, it accelerates.

And as there is evidence that the ocean is responding to atmospheric changes in temperature, both at the surface and at depth, the study suggests that “predicted future increases in ocean temperatures will result in reduced CO2 storage by the oceans”.

The research was conducted on a small scale, in a limited stretch of ocean, so the conclusion is still provisional − and, like all good science, will be confirmed by replication. But it is yet another instance of the self-sustaining momentum of global warming.

Such positive feedbacks are already at work in high latitudes. Ice reflects sunlight, and therefore the sun’s heat. So as the Arctic ice sheet steadily diminishes over the decades, more and more blue water is available to absorb heat − and accelerate warming.

“The world is at a crossroads in terms of climate health and climate change”

The same gradual warming has started to release another greenhouse gas trapped at the ocean’s edge. Natural “marsh gas”, or methane, is stored in huge masses, “frozen” as methane hydrate in cold continental shelves.

Methane exists in much smaller quantities than carbon dioxide, and has a shorter life in the atmosphere, but is far more potent, volume for volume, as a greenhouse gas.

Researchers at the Arctic University of Norway in Tromso reported last month in Geophysical Research Letters that once-frozen methane gas was leaking from thawing ocean floor off Siberia. Some of this thaw is natural, and perhaps inevitable. But some is connected with human influence and could accelerate.

Alexei Portnov, a geophysicists at the university’s Centre for Arctic Gas Hydrate, Climate and Environment  says: “If the temperature of the oceans increases by two degrees, as suggested by some reports, it will accelerate the thawing to the extreme. A warming climate could lead to an explosive gas release from the shallow areas.”

Biological origin

Arctic methane, like ocean organic carbon, has a biological origin. It is released by decaying vegetation under marshy conditions and tends to form as a kind of ice at low temperatures and high pressures, much of it along continental shelves that, at the height of the Ice Ages, were above sea level.

The International Union for Conservation of Nature also reminded the world last month that the ocean plays a vital role in climate, and that plankton, fish and crustaceans could be considered as “mobile carbon units”.

In this sense, the fish in the sea are not just suppers waiting to be caught, but are important parts of the planetary climate system. The healthier the oceans, and the richer they are in living things, the more effective they become at soaking up atmospheric carbon.

“The world is at a crossroads in terms of climate health and climate change,” said Dan Laffoley, vice-chairman of the IUCN World Commission on Protected Areas, introducing a new report on the marine role in the carbon cycle.

“Neglect the ocean and wonder why our actions are not effective, or manage and restore the ocean to boost food security and reduce the impact of climate change. The choice should be an easy one.” – Climate News Network

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Satellite provides sharper picture of shrinking ice sheet

Satellite provides sharper picture of shrinking ice sheet

The most detailed study yet of the Greenland ice sheet illustrates the complex process that is causing billions of tonnes to melt ever year.

LONDON, 27 December, 2014 − Greenland’s ice sheet shrank by an average of 243 billion tonnes a year between 2003 and 2009 – a rate of melting that is enough to raise the world’s sea levels by 0.68 mm per year.

In what is claimed as the first detailed study, geologist Beata Csatho, of the University of Buffalo in the US, and colleagues report in the Proceedings of the National Academy of Sciences that they used satellite and aerial data to reconstruct changes in the ice sheet at 100,000 places, and to confirm that the process of losing 277 cubic kilometres of ice a year is more complex than anyone had predicted.

The Greenland ice sheet is the second biggest body of ice on Earth − second only to Antarctica − and its role in the machinery of the northern hemisphere climate is profound.

Careful measurements

It has been closely studied for decades, but such are the conditions in the high Arctic that researchers have tended to make careful measurements of ice melt and glacier calving in fixed locations – in particular, at four glaciers − and then try to estimate what that might mean for the island as a whole.

“The great importance of our data is that, for the first time, we have a comprehensive picture of how all of Greenland’s glaciers have changed over the past decade,” Dr Csatho said.

The study looked at readings from NASA’s ice, cloud and land elevation satellite ICESat, and from aerial surveys of 242 glaciers wider than 1.5 km at their outlets, to get a more complete picture of melting, loss and – in some cases – thickening of the ice sheet as a whole.

“When the ice sheet is thinner, it is at a slightly lower elevation and at the mercy of warmer air temperatures”

Previous studies have focused on the four glaciers. One of them, Jakobshavn, has doubled its speed of flow since 2003, and closer studies have begun to reveal more about the dynamics of individual flows.

But the real strength of the study is that it establishes the pattern of ice melt in more detail, and suggests that climate models may not give a clear enough picture of the future of the ice cap. To put it crudely, Greenland could lose ice faster in the future than any of today’s predictions suggest.

Meanwhile, a team from the UK has been trying to work out what is happening on the surface of the ice sheet. Each summer, of course, some of the ice melts. Some of this gets to the sea, but some freezes again in the natural seasonal order of things.

But glaciology researcher Amber Leeson, of the University of Leeds, and colleagues report in Nature Climate Change that the “supraglacial” lakes that form each summer could also affect ice flow.

Their computer simulations suggest that these lakes will migrate further inland as the century wears on and the world continues to warm. Ice reflects heat, water absorbs it. So the process could trigger further melting. Some of this extra meltwater could slide or drain to the base of the glacier, lubricating its flow and accelerating the process yet again.

Thin pancake

“Our research shows that, by 2060, the area of Greenland covered by them will double,” Dr Leeson said. “When you pour pancake batter into a pan, if it rushes quickly to the edge of the pan, you end up with a thin pancake. It’s similar to what happens with ice sheets. The faster it flows, the thinner it will be.

“When the ice sheet is thinner, it is at a slightly lower elevation and at the mercy of warmer air temperatures than it would be if it were thicker, increasing the size of the melt zone around the edge of the ice sheet.”

In the last 40 years, the band in which such supraglacial lakes can form has crept 56 km inland. By 2060, the simulations now suggest, it could reach 110km inland, doubling the area of coverage and delivering yet more meltwater to fuel further warming.

Once again, the research suggests that current models underestimate the rate of ice loss. – Climate News Network

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Polar bears feel the heat as frozen habitat shrinks

Polar bears feel the heat as frozen habitat shrinks

As climate change increasingly affects the Arctic, some polar bear populations are suffering because rising temperatures are reducing the sea ice vital for their survival.

LONDON, 19 December, 2014 − The Arctic is changing faster under the influence of the warming climate than anywhere else on Earth, scientists have confirmed.

The US National Oceanic and Atmospheric Administration (NOAA) says Arctic air temperatures continue to rise more than twice as fast as they do globally − a phenomenon known as Arctic amplification.

The extent of snow cover in April 2014 in Eurasia was the lowest since 1967, and sea ice extent in September was the sixth lowest since 1979.

Badly affected

Some Arctic polar bear populations have been badly affected by the progressive shrinking of Arctic sea ice.

But NOAA says: “Natural variation remains, such as the slight increase in March 2014 sea ice thickness and only a slight decrease in total mass of the Greenland ice sheet in summer 2014.”

Increasing air and sea surface temperatures, a decline in the reflectivity of the ice at the surface of the Greenland ice sheet, shrinking spring snow cover on land and summer ice on the ocean, and the declining populations and worsening health of some bear populations are among the findings described in NOAA’s Arctic Report Card 2014.

“Arctic warming is setting off changes that affect people and the environment in this fragile region, and has broader effects beyond the Arctic on global security, trade and climate,” Craig McLean, of NOAA, told the annual American Geophysical Union Fall meeting in San Francisco.

“This year’s Arctic Report Card shows the importance of international collaboration on long-term observing programmes that can provide vital information to citizens, policymakers and industry.”

“Arctic warming has broader effects beyond the Arctic on global security, trade and climate”

The Report Card, published annually since 2006, updates changes affecting the Arctic. This year’s report − written by 63 US and other authors − covers key indicators, and also includes a new report on the status of the bears.

This section, written by the Norwegian Polar Institute and Polar Bears International, assesses the animals’ populations in some areas where there is good long-term data available. There are clear variations between areas.

Ice break-up

The most recent data shows that a population decline in western Hudson Bay, Canada, was caused by earlier sea ice break-up and later freeze-up.

The bears depend on sea ice to travel, hunt, mate and, in some areas, to den. But in the southern Beaufort Sea, north of Alaska, their numbers have now stabilised after a decline of about 40% since 2001.

In the Chukchi Sea, between Alaska and Russia and immediately to the west of the Beaufort, the condition of the bears and their reproductive rates have been stable for 20 years.

The Report Card says there are now twice as many ice-free days in the southern Beaufort as there are in the Chukchi Sea.

It notes that polar bears have been through “long and dramatic periods of population decline” during the last million years, and that during periods with little sea ice, polar bears and brown bears have often interbred.

The report says Alaska recorded temperature anomalies more than 10°C higher than the January average during 2014.

Snow cover across the Arctic during the spring was below the long-term average for 1981-2010, with a new record low set in April for Eurasia. North America’s June snow extent was the third lowest on record.

Snow disappeared three to four weeks earlier than normal in western Russia, Scandinavia, the Canadian sub-Arctic and western Alaska because of below-average accumulation and above-normal spring temperatures.

The eight lowest sea ice extents since 1979 have occurred in the last eight years (2007-2014). There is still much less of the oldest, thickest (greater than 13 feet, or four metres) and most resilient ice than in 1988, when it made up 26% of the ice pack. This year’s figure is 10%.

Extent of melting

As sea ice retreats in summer, sea surface temperature across the Arctic Ocean is increasing. In the Chukchi Sea, it is increasing at 0.5°C per decade.

Melting occurred across almost 40% of the surface of the Greenland ice sheet in summer 2014. For 90% of the summer, the extent of melting was above the long-term average for 1981-2010.

In August 2014, the reflectivity (albedo) of the ice sheet was the lowest recorded since satellite observations began in 2000. When less of the sun’s energy is reflected by ice, melting increases. The total mass of the ice sheet remained essentially unchanged between 2013 and 2014.

Declining sea ice allows more sunlight to reach the upper layers of the ocean, triggering increased photosynthesis and greater production of phytoplankton − the tiny marine plants that form the base of the food chain for fish and marine mammals. − Climate News Network

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Deep concern over invisible threat to Antarctic glaciers

Deep concern over invisible threat to Antarctic glaciers

As ocean temperatures rise, warmer currents are attacking the Antarctic ice sheet from below and adding to the threats posed by a melting rate that has trebled in the last two decades.

LONDON, 13 December, 2014 − The Antarctic ice shelf is under threat from a silent, invisible agency – and the rate of melting of glaciers has trebled in the last two decades.

The ocean waters of the deep circumpolar current that swirl around the continent have been getting measurably warmer and nearer the ocean surface over the last 40 years, and now they could be accelerating glacier flow by melting the ice from underneath, according to new research.

And a separate study reports that the melting of the West Antarctic glaciers has accelerated threefold in the last 21 years.

Calamitous consequences

If the West Antarctic ice sheet were to melt altogether – something that is not likely to happen this century – the world’s sea levels would rise by 4.8 metres, with calamitous consequences for seaboard cities and communities everywhere.

Researchers from Germany, Britain, Japan and the US report in Science journal that they base their research on long-term studies of seawater temperature and salinity sampled from the Antarctic continental shelf.

This continued intrusion of warmer waters has accelerated the melting of glaciers in West Antarctica, and there is no indication that the trend is likely to reverse.

Other parts of the continent so far are stable – but they could start melting for the first time.

“The Antarctic ice sheet is a giant water reservoir,” said Karen Heywood, professor of environmental sciences at the University of East Anglia, UK. “The ice cap on the southern continent is on average 2,100 metres thick and contains 70% of the world’s fresh water. If this ice mass were to melt completely, it could raise global sea level by 60 metres. That is not going to happen, but it gives you an idea of how much water is stored there.”

“These waters have warmed . . . and  are significantly shallower than 50 years ago”

Temperatures in the warmest waters in the Bellinghausen Sea in West Antarctica have risen from 0.8°C in the 1970s to about 1.2°C in the last few years.

“This might not sound much, but it is a large amount of extra heat available to melt the ice,” said Sunke Schmidtko, an oceanographer at the Geomar Helmholtz Centre for Ocean Research in Kiel, Germany, who led the study. “These waters have warmed in West Antarctica over 50 years. And they are significantly shallower than 50 years ago.”

The apparent rise of warm water, and the observed melting of the West Antarctic ice shelf, could be linked to long-term changes in wind patterns in the southern ocean. Although melting has not yet been observed in other parts of the continent, there could be serious consequences for other ice shelves.

The shelf areas are where the Antarctic krill – the little shrimp that plays a vital role in the Antarctic ocean food chain – are getting warmer, with unpredictable consequences for spawning cycles, and then for ocean biodiversity.

Meanwhile, according to US scientists writing in Geophysical Research Letters, the glaciers of the Amundsen Sea in West Antarctica are shedding ice faster than any other part of the region.

Tyler Sutterley, a climate researcher at the University of California Irvine, and NASA space agency colleagues used four sets of observations to confirm the threefold acceleration.

They took their data from NASA’s Gravity Recovery and Climate Experiment (GRACE) satellites, from a NASA airborne project called Operation IceBridge, from an earlier satellite called ICESat, and from readings by the European Space Agency’s Envisat satellite.

Loss calculated

The observations spanned the period 1992 to 2013 and enabled the researchers to calculate the total loss of ice, and also the rate of change of that loss.

In all, during that period the continent lost 83 gigatonnes, or 83 billion metric tonnes, of ice per year on average. Since Mount Everest weighs an estimated 161 billion tonnes, this is as if the ice cap lost an Everest’s worth of ice every two years.

After 1992, the rate of loss accelerated by 6.1 billion tonnes a year, and between 2003 and 2009 the melt rate increased by 16.3 gigatonnes a year on average. So the increasing rate of loss is now nearly three times the original figure.

“The mass loss of these glaciers is increasing at an amazing rate,” said Isabella Velicogna, Earth system scientist at both UC Irvine and the NASA Jet Propulsion Laboratory. – Climate News Network

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Why Greenland is likely to melt more quickly

Why Greenland is likely to melt more quickly

Scientists who have examined the role of the bedrock on which the Greenland ice sheet rests think it shows the huge island is more vulnerable than realised to global warming.

LONDON, 1 October – Climate scientists have thought a little more deeply about the state of the Greenland ice sheet and their conclusions are ominous.

They think that the northern hemisphere’s largest assembly of ice and compacted snow is more vulnerable to climate change than anybody had previously thought.

Marion Bougamont of the Scott Polar Research Institute in Cambridge, UK, and colleagues report in Nature Communications that they factored in not just a mathematical model of the melting ice from Greenland, but also the role of the soft, yielding and absorbent mud and rock beneath.

The Greenland ice sheet is the planet’s second largest body of terrestrial ice. It covers 1.7 million square kilometres and if it were all to melt, the world’s sea levels would rise by more than seven metres.

Right now, about 200 gigatonnes of Greenland ice a year turn to water and run into the sea. This alone raises sea levels at the rate of 0.6 millimetres a year. In fact the increase in sea levels from all causes – glacier retreat worldwide, ice cap melting and ocean thermal expansion –  is now 3 mm a year.

Researchers have repeatedly found evidence of an acceleration of melting, in some cases by looking at what is happening within the ice or on the surface, or by taking a new look at satellite data.

Less stable

But the latest calculation goes even deeper: into the mud below the ice. According to the new model, and to evidence from surveys, melting will be complicated by the conditions deep under the ice.

The ice sheets are moving, naturally and at different speeds, causing the ice to shear or flow, and the assumption has always been that the ice is flowing over hard and impermeable rock. A closer look suggests a different process.

Lakes of summer meltwater tend to form on the ice sheet surface: if the ice below fractures, these lakes can drain in a matter of hours. The meltwater flows down within the ice, and into the sediment below it.

“The soft sediment gets weaker as it tries to soak up more water, making it less resistant, so that the ice above moves faster. The Greenland ice sheet is not nearly as stable as we think,” said Poul Christofferson, a co-author.

And Dr Bougamont said: “There are two sources of net ice loss: melting on the surface and increased flow of the ice itself, and there is a connection between these mechanisms that isn’t taken into account by standard ice sheet models.”

Rapid change

At present, the annual flow of ice meltwater is more or less stable. In warmer years, the ice sheet becomes more vulnerable because more meltwater gets to the muddy absorbent bedrock. Because there is a limit to how much the sediment below can hold, the ice sheet becomes more vulnerable during extreme events such as heat waves.

And, of course, if under such a scenario it is vulnerable, it continues to become more vulnerable as average temperatures rise and extreme events become more frequent, and more extreme. And a closer look at recent geological history shows just how fast change can happen.

In a separate study in Nature Communications, Katharine Grant of the Australian National University and colleagues report that they examined evidence of the melting process at the close of each of the last five ice ages.

They looked at data from wind-blown dust in sediment cores from the Red Sea, and matched these with records from Chinese stalagmites to confirm a picture of pronounced climate change at the end of each ice age, and calculated that sea levels rose at the rate of 5.5 metres per century.

These however were exceptional events, and there were more than 100 smaller sea level events in between the big five.

“Time periods with less than twice the modern global ice volume show almost no indications of sea level rise faster than about 2 metres per century,” said Dr Grant. “Those with close to the modern amount of ice on Earth show rates of up to one to 1.5 metres per century.” – Climate News Network

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Ice melt dilutes Arctic sea’s CO2 clean-up role

Ice melt dilutes Arctic sea’s CO2 clean-up role

New scientific research confirms that global warming is melting increasingly larger areas of Arctic sea ice − and reducing its vital function of removing CO2 from the atmosphere.

LONDON, 26 September, 2014 − The Arctic ice cap has just passed its summer minimum – and it’s the sixth lowest measure of sea ice recorded since 1978, according to scientists at the US space agency NASA.

For three decades, the shrinking Arctic ice – and the growing area of clear blue water exposed each summer – has been a cause of increasing alarm to climate scientists.

Polar seasonal changes are measured annually by NASA, but reliable satellite data goes back only to 1978, For much of the 20th century, the Arctic was part of the Cold War zone, so only Soviet naval icebreakers and US nuclear submarines took consistent measurements − and neither side published the data.

But studies of 17th and 18th century whaling ships’ logbooks and other records make it clear that the ice once stretched much further south each summer than it does today.

Steady decline

In the last 30 years, the thickness and the area of the ice have both been in steady decline, with predictions that in a few decades the Arctic Ocean could be virtually ice free by September, opening up new sea routes between Asia and Europe.

This year could have been worse, although the area of ice fell to little more than 5 million square kilometres − significantly below the 1981-2010 average of 6.22 million sq km.

“The summer started off relatively cool, and lacked the big storms or persistent winds that can break up ice and increase melting,” said Walter Meier, a research scientists at NASA’s Goddard Space Flight Centre. “Even with a relatively cool year, the ice is so much thinner than it used to be. It is more susceptible to melting.”

Warming in the Arctic is likely to affect climate patterns in the temperate zones, and the state of the polar ice has become of such concern that researchers are using ground-based and sea-based monitors to explore the physics of the phenomenon.

But there is another reason for the attention: as polar ice diminishes, so does the planet’s albedo − its ability to reflect sunlight back into space.

So, as the ice shrinks, the seas warm, making it more difficult for new ice to form. And greater exposure to sunlight increases the probability that permafrost will thaw, releasing even more greenhouse gases locked in the frozen soils.

Now researchers have found another and unexpected example of climate feedback that could affect the cycle of warming. Climate scientist Dorte Haubjerg Søgaard, of the Greenland Institute of Natural Resources and the University of Southern Denmark, and research colleagues have discovered that sea ice itself is an agency that removes carbon dioxide from the atmosphere.

That the oceans absorb the stuff, and tuck it away as calcium carbonate or other marine minerals, is old news.

“But we also thought that this did not apply to ocean areas covered by ice, because the ice was considered impenetrable,” Søgaard said. “However, new research shows that sea ice in the Arctic draws large amounts of CO2 from the atmosphere into the ocean.”

The research is published in four journals, Polar Biology, The Cryosphere, The Journal of Geophysical Research: Atmospheres and Marine Ecology Progress Series.

Two-stage pattern

The Danish research team observed a complex, two-stage pattern of gas exchange as ice floes formed off southern Greenland. They measured the role of atmospheric carbon dioxide in the formation and release of calcium carbonate crystals form in the sea ice, and kept a tally during a 71-day cycle of the carbon dioxide budget.

In the course of this complicated bit of natural cryo-chemistry, they found that some CO2 was carried deep into the ocean with dense, heavy brines, as the ice froze and some was captured by algae in the thawing ice.

They also identified a third factor: the “frost flowers” that formed on the new ice had an unexpectedly high concentration of calcium carbonate.

The profit-and-loss accounting meant that every square metre of ice effectively removed 56 milligrams of carbon from the atmosphere during the 71-day cycle. Over an area of 5 million sq km, this would represent a significant uptake.

But the real importance of the discovery is that scientists have identified yet another way in which the ice – while it is there – helps keep the Arctic cold, and yet another way in which carbon dioxide is absorbed by the oceans.

“If our results are representative, then the sea ice plays a greater role than expected, and we should take account of this in future global CO2 budgets,” Søgaard said. – Climate News Network

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