Tag Archives: Oceans

Hi-tech quest for Arctic sea ice answers

Walrus surfacing through sea ice off the Alaska coast Image: Joel Garlich Miller/USFWS via Wikimedia Commons
Breakthrough: walrus surfacing in sea ice off the coast of Alaska
Image: Joel Garlich Miller/USFWS via Wikimedia Commons

By Tim Radford

A sophisticated array of automatic sensors will allow scientists to conduct the longest ever monitoring programme to determine the precise physics of summer sea ice melt in the Arctic.

LONDON, 20 July, 2014 − An international team of scientists plan to spend months watching ice melt. But although it will take longer and cost a lot more than watching paint dry, it will be much more interesting and rewarding.

They plan to discover just how the Arctic ice retreats, the rate at which it melts, and the oceanographic processes at work.

The Arctic ice cap is a vital part of the climate machine, and the basis of an important ecosystem. But although the polar ice once stretched far further south, it has been both thinning and shrinking for more than three decades. This melting shows signs of accelerating, with consequences for nations far to the south, but researchers still don’t know much about the physics of the process.

Suite of technologies

So the US Naval Research Laboratory, oceanographers from France and the US, the British Antarctic Survey, the Korean Polar Research Institute, the Scottish Association for Marine Science, and the Universities of Cambridge in the UK and Yale in the US have co-ordinated a suite of technologies to monitor every detail of this summer’s ice retreat from the Alaskan shoreline, northwards.

They will use an array of floats, buoys, sensors, thermometers, tethers, GPS receivers and automated weather stations to measure every detail, such as the flow of warmer water, growth and pattern of waves, the wind speed and direction, air pressure, and humidity.

There will be buoys fixed in the ice to record both the melting and – later in the year – its refreezing, and an array of ice-tethered profilers to monitor the changes in the upper ocean. Autonomous sea gliders, too, will be released to explore below the ice shelf and report back every time they surface.

The Arctic summer ice is an example of positive feedback. Ice reflects sunlight, so it is its own insulator, and keeps itself cold. But as it melts and retreats, the exposed darker ocean waters can absorb more radiation, and bring more warmth to the edges of the retreating ice, thus accelerating the process.

It freezes again, but – on average – each year the ice cap becomes thinner, and the total area frozen continues to shrink. Researchers think they understand the big picture, but now they want the confirmatory fine detail.

Melt season

“This has never been done at this level, over such a large area and for such a long period of time,” said Craig Lee, of the University of Washington, who leads the Marginal Ice Zone Programme project. “We’re really trying to resolve the physics over the course of an entire melt season.”

The project began in March, when researchers planted an array of sensors along a line 200 miles to the north of Alaska. In August, a Korean icebreaker will install more equipment, and a team from Miami is studying high resolution satellite pictures of ice floes in the region. Biologists will also want to understand the effect of temperature changes on marine micro-organisms.

“The field programme will provide unique insight into the processes driving the summer melt of Arctic ice,” Dr Lee said. “It’s the automation and unprecedented collaboration that allows us to be out there for the entire season. You couldn’t afford to be out there at this intensity, for this length of time, any other way.” − Climate News Network

New clue to Antarctic food-web puzzle

Strength in numbers: thousands of Adélie penguins at a rookery Image: Michael Van Woert/NOAA NESDIS, ORA via Wikimedia Commons
Strength in numbers: thousands of Adélie penguins in an Antarctic rookery
Image: Michael Van Woert/NOAA NESDIS, ORA via Wikimedia Commons

By Tim Radford

A landmark research study that shows one species of penguin is thriving while other populations are in rapid decline offers new insight into how climate change is affecting Antarctica.

LONDON, 16 July, 2014 − Good news from Antarctica: the continent may be warming, the ice shelf may be at risk, and the food chain may ultimately become precarious, but the Adélie penguin population – at least for the moment − is higher than ever before.

The news does not suggest that global warming and climate change are actually good for this important indicator species, which has certainly been in decline on the Antarctic Peninsula. But it does represent an advance: for the first time, a comprehensive study has concluded with a full census of the species.

Heather Lynch, assistant professor of ecology and evelotion at Stony Brook University in New York, and Michelle La Rue, research fellow at the University of Minnesota’s Polar Geopspatial Center, used high resolution satellite imagery to measure levels of penguin guano – the fertiliser industry’s preferred term for seabird excrement – on the continent.

They then used that as the basis for calculating the numbers of birds in a colony necessary to account for all that digested and evacuated seafood.

They report in a journal called The Auk: Ornithological Advances that they identified at least 17 populations of Adélie penguins not previously known to exist, but failed to pinpoint 13 already-recorded colonies, and declared eight of them eradicated.

Their estimate for the total Adélie population in and around the Southern Ocean stands at 3.79 million, which is 53% higher than all previous estimates.

Useful evidence

The researchers call their work a “landmark” study, and see it not as evidence that climate change is going to work for the benefit of one particular species, but more as a useful piece of the great food-web puzzle in a changing climate.

Penguins have been in rapid decline in the West Antarctic Peninsula, which has become one of the fastest-warming regions on the planet. Warmer weather and increased rain have already started to take toll of Magellanic penguins in Argentina, and researchers recently predicted long-term decline for the iconic Emperor penguin on Antarctica itself.

But this is only long-term decline. As long as Antarctica stays cold and the ice shelf stays stable, the researchers say, the population could, in the short term, actually rise.

That is because what matters most to the species that nest in Antarctica is the supply of fish and krill around the continent’s edge. The health and resilience of the Adélie population – and the Emperor penguin, the leopard seal, the cetaceans, and so on – ultimately depend on how the krill and fish populations respond to climate change.

Humans, too, fish for commercial supplies of Antarctic krill, which provides a source of food for fish farms.

“Our finding of a 53% increase in Adélie penguin breeding abundance, compared to 20 years ago, suggests that estimates of krill consumption by this species may be seriously underestimated,” Dr Lynch said. “Leaving enough prey for natural krill predators is an important element in ensuring fisheries proceed sustainably.”

But a second team confirms in Nature Communications that there are strong links between climate and marine life, and that changes in factors such as wind speed and sea ice can have knock-on effects right around the Antarctic food web.

Since 1990, scientists aboard US research vessels have been conducting annual surveys along the western side of the Antarctic Peninsula, measuring populations of photosynthetic algae.

These peak every four to six years, according to changes in atmospheric pressure between the mid-latitudes and Antarctica itself.

Glacial meltwater

In winter, when cold southerly winds blow across the Peninsula, the winter ice extends. Winds drop from spring to summer, reducing the retreat of the ice. So the water column in summer then is stable, and the phytoplankton multiply, fed by iron-rich glacial meltwater.

The blooms of phytoplankton are what the krill need to multiply, and when the krill are around in huge volumes, the Adélie and other penguins, fur seals, baleen whales and albatross don’t have to go so far to find food.

But marine scientist Grace Saba, who did her research while with the Virginia Institute of Marine Science, before moving to Rutgers University, New Jersey, reports that these ideal conditions – negative phases of the Southern Annular Mode (SAM), to give it the technical terminology – are not guaranteed in future. If the world goes on burning fossil fuels, conditions will probably change.

“Projections from global climate models under business-as-usual emission scenarios up to the year 2100 suggest a further increase in temperature and in the occurrence of positive-SAM conditions,” Dr Saba said.

“If even one positive SAM episode lasted longer than the krill lifespan – four to six years with decreased phytoplankton abundance and krill recruitment – it could be catastrophic to the krill population.”  − Climate News Network

Coastal warning for vital Atlantic habitats

Kelp fringes the coast of Jura off north-east Scotland. Image: Patrick Mackie/geograph.org.uk via Wikimedia Commons
Thick kelp beds fringe the rocky coast of the Scottish island of Jura
Image: Patrick Mackie/geograph.org.uk via Wikimedia Commons

 By Tim Radford

Some of the world’s most productive marine habitats are seriously at risk as scientists say that CO2-related changes and human activities threaten to destroy vital kelp fields and maerl beds in the north-east Atlantic’s coastal waters

 

LONDON, 26 June, 2014 − Rising temperatures, increasingly acidic seas and human destruction will drastically change the nature of the coastal seas of the north-east Atlantic over the next century, scientists predict.

According to new research in the journal Ecology and Evolution, it will completely alter the forests of kelp and the maerl beds of coralline algae that serve as shelter and nurseries for baby cod and juvenile scallops. These are some of the most productive habitats on Earth − habitats that also soak up carbon from the atmosphere and deliver the primary production for thriving communities of sea creatures.

Juliet Brodie, research chair of the Department of Botany at the Natural History Museum, London, reports with colleagues that their study considered changes in water chemistry, the steady rise in water temperatures, and the pattern of destruction in the northern seas − by fishermen, dredgers and pollutants. They then calculated the likely outcomes.

Invasive species

“We predict that, by 2100, warming will kill off the kelp forest in the south, ocean acidification will remove maerl beds in the north, and invasive species will thrive,” the report warns.

The sea grasses will survive only if they are protected from dredging and other human impacts. As habitats disappear, native species will perish with them, and invasive species will thrive.

Jason Hall-Spencer, a study team member and professor of marine biology at Plymouth University, UK,, said: “What we find most staggering is how fast warming and the spread of corrosive waters will alter marine life around out coasts. Our shores will look very different in coming years, affecting people who make a living from the seas.”

The scientists built up a picture of the future from a study of existing research, and they concentrated on the primary producers: the plants that build up tissues from atmospheric carbon, and provide the provender and protection for a host of other species.

Significant role

Kelp forests are among the most productive habitats in the seas. Studies have found that these great, fleshy algae can consume more than a kilogram of carbon per square metre per year, so they play a significant role in the carbon cycle, and help to modify climate change.

Kelps and other seaweed species are adapted to cool waters and, as the seas warm, are predicted to become increasingly stressed. As these weaken, they will steadily be replaced by invaders from other climates. Researchers have already identified 44 species of non-native algae in the north-east Atlantic.

“Carbon dioxide emissions are causing rates of global warming and ocean acidification that will profoundly affect marine flora worldwide,” the scientists conclude.

And they warn that, unless action is taken, societies will “sleepwalk through radical ecological changes” to the plantlife of the European coasts. – Climate News Network

Icebergs strip away rich Antarctic habitat

Icy waters near the Rothera research station in Antarctica Image: Vincent van Zeijst via Wikimedia Commons
Icy waters near the Rothera research station in West Antarctica
Image: Vincent van Zeijst via Wikimedia Commons

By Tim Radford

The scouring effect of drifting icebergs that are increasingly breaking free from Antarctic ice shelves as a result of global warming is wiping out fauna that cling to the boulders in shallow waters

 LONDON, 23 June, 2014 − A once-rich habitat in the Antarctic has become an impoverished zone as icebergs, increasingly breaking free from the surrounding sea ice because of global warming, scour the shallow-water rocks and boulders on which a diversity of creatures cling to life.

A report in the journal Current Biology says that researchers who carried out a survey dive in 2013 at Lagoon Island, off the West Antarctic Peninsula, discovered that “no live mega or macro-fauna can be found, the first time this has been observed there, despite being regularly visited by scientific divers since 1997”.

David Barnes, of the British Antarctic Survey, and colleagues report that boulders on the seabed near the Rothera research station had once been richly encrusted with creatures that competed for living space. Now such rocks might only support a single species.

Early warning system

“The Antarctic Peninsula can be considered an early warning system, like a canary in a coal mine,” Dr Barnes said. “Physical changes there are among the most extreme and the biology considered quite sensitive, so it was always likely to be a good place to observe impacts of climate change.

“But impacts elsewhere are likely to be not too far behind. A lot of the planet depends on the near shore environment, not least for food. What happens there to make it less stable is important.”

A research diver surveys the shallow waters of West Antarctica Image: British Antarctic Survey
A research diver surveys the shallow waters off the West Antarctic Peninsula
Image: British Antarctic Survey

Climate change has already begun to affect Antarctica in different ways. Researchers last year found that as icebergs broke free, the surviving ice shelf had begun to melt from underneath from underneath. The effect of the drifting bergs was mixed: at depth in the fjords of the Peninsula, for instance, the species variety seemed to have got richer, according to one set of observations.

But no such effect was observed in the ocean shallows that are being scraped and scoured by drifting icebergs. The researchers say that although no species has disappeared entirely from the region, the numbers are so low as to be negligible.

In 2013, most of the observations seemed to involve just one opportunistic or pioneer species, a suspension feeder called Fenstrulina rugula. What had once been a rich habitat had become one of the simplest seabed systems to be found anywhere.

Ecological roles

“Reduction of complex systems into very simple ones, where many (formerly important) species become too rare to maintain meaningful ecological roles, is a common reaction to anthropogenic disturbance such as overfishing, pollution, introductions of non-indigenous species, and habitat destruction,” the report’s authors say.

“Across West Antarctica, the levels of these disturbances are among the lowest globally, apart from greenhouse contributions to climate change.”

The scientists conclude: “We expect the deeper seabed to become richer in benthic colonisation with more ice shelf collapses and fast ice losses, but hard surfaces in the shallows are likely to become deserts dominated by rapidly-colonising pioneers and responsive scavengers.” − Climate News Network

May days’ heat sets up record El Niño

 

Flooding in California during the “El Niño of the century” in 1998 Image: Dave Gatley/FEMA via Wikimedia Commons
Flooding in California during the “El Niño of the century” in 1998
Image: Dave Gatley/FEMA via Wikimedia Commons

By Tim Radford

Scientists believe that soaring global temperatures during an unusually hot month of May may have created the ideal conditions to provide a warm welcome for an El Niño weather phenomenon that will break records

LONDON, 20 June, 2014 − Last month was the third warmest May since NASA satellites began taking the temperature of the planet 35 years ago, and was also the warmest May that did not fall within an El Niño Pacific warming event – which could mean a record-breaking appearance this year by the fearsome “Child”.

Scientists in the US says the global average was 0.33°C warmer than the seasonal norms for the month. The warmest May ever was in 1998 during the “El Niño of the century”, when global average temperatures rose by 0.56°C, and the second warmest at 0.45°C was in 2010, another El Niño year.

So if indications are correct that an El Niño event is taking shape in the Pacific right now off the equatorial coast of South America, then it could become a record-setter − even if it isn’t a very spectacular event − just because it will get a warmer start, according to John Christy, professor of atmospheric science at the University of Alabama in Huntsville, US.

Temperature patterns

An El Niño (Spanish for The Child, because it was first observed by Peruvian fishermen around Christmas) is a shift in the temperature patterns of the Pacific, as a blister of equatorial ocean heat moves eastwards. It is a natural cyclic event that tends to reverse the prevailing Pacific weather patterns, often damagingly, and is not connected with climate change  although its effects could be made worse by climate change.

“The long-term baseline temperature is about three tenths of a degree warmer than it was when the big El Niño of 1997-1998 began, and that event set the one month record,” Christy said. “With the baseline so much warmer, this upcoming El Niño won’t have very far to go to break that 0.66°C record. That isn’t to say it will, but even an average-sized warming event will have a chance to get close to that level.”

Meanwhile, according to new research in Nature Climate Change, people in the northern hemisphere can also expect warmer temperatures in autumn and winter – in spite of last winter’s spectacular ice storms in the US north-east that shut down cities from the Atlantic to the Midwest, and where − to the joy of headline writers − the town of Hell in Michigan froze over.

Extremes of cold

The report’s author, James Screen, Natural Environment Research Council research fellow at the University of Exeter, UK, says that even though there will be extremes of cold, these will be less frequent and less severe. The Arctic is warming, and a study of autumn and winter temperature variations shows that variability in the temperate zone overall has in fact decreased.

“Autumn and winter days are becoming warmer on average, and less variable from day to day,” Dr Screen said. “Both factors reduce the chance of extremely cold days.

“Cold days tend to occur when the wind is blowing from the north, bringing Arctic air south into the mid-latitudes. Because the Arctic air is warming so rapidly, these cold days are now less cold than they were in the past.” – 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

‘End high seas fishing for climate’s sake’

End of the line for the high seas fleets? It seems utopian, but there'd be benefits Image: Sensor via Wikimedia Commons

End of the line for the high seas fleets? It seems utopian, but there’d be benefits
Image: Sensor via Wikimedia Commons

Two scientists say fish from the high seas are too valuable to be eaten, because they lessen climate change through the carbon they consume.

LONDON, 8 June – Marine biologists have delivered the most radical proposal yet to protect biodiversity and sequester carbon: stop all fishing, they say, on the high seas.

The high seas are the stretches of ocean that nobody owns and nobody claims: they are beyond the 200-mile economic zones patrolled and sometimes disputed by national governments. They are also what climate scientists call a carbon sink, a natural source of carbon removal.

Life in the deep seas absorbs 1.5 billion tonnes of carbon dioxide from the atmosphere and buries half a billion tonnes of carbon on the sea bed every year, according to Rashid Sumaila of the University of British Columbia in Canada and Alex Rogers of the University of Oxford in the UK. The two researchers put the value to humanity of life in the high seas – in terms of its ability to sequester carbon – at $148 billion a year.

Only a hundredth of the fish landed in all the ports in all the world is found on the high seas alone. And around 10 million tonnes of fish are caught by high seas fishing fleets each year, and sold for $16bn.

“Countries around the world are struggling to find cost-effective ways to reduce their carbon emissions. We’ve found that the high seas are a natural system that is doing a good job of it for free,” said Professor Sumaila.

“Keeping fish in the high seas gives us more value than catching them. If we lose the life on the high seas, we’ll have to find another way to reduce emissions at a much higher cost.”

Staying in the depths

But it isn’t just the high seas that sequester carbon. In a second study, published in the Proceedings of the Royal Society B, British and Irish researchers argue that deep sea fish remove and stow away more than a million tonnes of carbon dioxide just from waters around the British coasts and the Irish Sea. If this volume were valued as “carbon credits” it would add up to £10mn a year ($16.8mn).

The reasoning goes like this. Deep water fishes don’t rise to the surface, they depend on food that filters down to them from above. At mid water level, there is a huge and diverse ecosystem involving many species that rise to the surface to feed during the night and then sink back down again, and some of this reaches the depths.

Clive Trueman of the University of Southampton and colleagues measured ratios of isotopes of carbon and nitrogen in the tissues of fish caught at depths between 500 and 1800 metres to calculate the original sources of food: more than half of these fish got their energy – their food supply – from fishes that went to the surface. But deep water fish, when they die, stay at depth. Their carbon doesn’t get back into the atmospheric system.

Research like this is done to solve the puzzles of the planetary ecosystem, but also to explore the options open to politicians who will one day have to confront the mounting costs of climate change.

The declaration of the high seas as “off limits” to all fishing sounds utopian, but fisheries scientists have repeatedly argued that present fishing regimes are not sustainable, and that radical steps must be taken.

Fish sanctuaries

Callum Roberts, of the University of York, UK, has been making the case for “marine parks”, or undisturbed ocean and shallow water wildernesses, for more than a decade.

Like pristine tropical rainforests, or protected wetlands and prairies, these would be nurseries and safe zones for rare or otherwise threatened species of plants and animals. But they would also serve as valuable carbon sinks. Either way, humans would benefit because the marine parks would slow global warming and limit climate change.

“The more abundant life is, and the more the seabeds are rich, complex and dominated by filter feeders that extract organic matter from the water, and creatures that bury matter in the mud, the more effective the seas will be as a carbon sink. Overfishing has diminished that benefit wherever it has taken place just at the time when we need it most,” Professor Roberts  told Climate News Network.

“I think the carbon sequestration argument is a strong one. The deep sea is probably the biggest carbon sink on the planet by virtue of its enormous size.

“It is incredibly important as a sink, because once carbon is trapped there, it is much harder for it to get re-released into the atmosphere than is the case for carbon sinks on land, like forests or peat bogs.”

Planetary benefits

Protection of fish on the high seas would also be good for fish stocks in the exclusive economic zones nearer the shores, where the global catch is more carefully managed, and where some areas are already protected.

This would benefit all nations where people depend on fishing or fish farming. At the moment, only a small number of nations maintain high seas fleets.

The Global Ocean Commission, which commissioned the high seas study,  claims that such a decision would make economic, social and ecological sense: the oceans supply “vital services” to humanity. They provide half of the planet’s oxygen, deliver nourishment for billions of people, and regulate the climate.

To protect the high seas could help offshore fish stocks, but demand for fish is likely to grow in step with population increases, and fish produce at least one sixth of the animal protein that humans consume.

The supply of “wild” fish caught by net or line peaked nearly two decades ago. The World Resources Institute believes that production of farmed fish and shellfish will have to increase by 133% by 2050. – 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

Migrating cyclones pose new threat

FOR IMMEDIATE RELEASE

 

A washed out section of New York's Rockwell subway track after Hurricane Sandy hit in 2012 Image: Leonard Wiggins/MTA New York City Transit via Wikimedia Commons

Washed out track on New York’s Rockaway subway line after Hurricane Sandy hit in 2012
Image: Leonard Wiggins/MTA New York City Transit via Wikimedia Commons

By Tim Radford

The world’s most destructive storms are on the move – putting at risk coastal areas that would not expect to be hit by violent hurricanes or typhoons.

LONDON, 20 May − Tropical cyclones – hurricanes in the Caribbean, typhoons in the South China Sea – are moving further north and south, threatening to create new havoc in unsuspecting coastal areas.

New research published in the journal Nature reveals that, on average, the storms have been migrating towards the poles at the rate of 53 kilometres a decade in the northern hemisphere, and 62 kilometres in the southern.

This means that landfalls that in the past that would not have expected violent storms will become increasingly at risk − “with obvious effects on coastal residents and infrastructure”, the paper says.

Jim Kossin, an atmospheric research scientist at the US National Oceanic and Atmospheric Administration (NOAA), and colleagues looked at data for the last 30 years and measured the latitudes as which storms reached their peak intensity. They found an uneven but measurable shift of around half a degree of latitude every 10 years.

The news makes sense, as researchers have previously identified a steady “expansion” of the tropics as a result of global warming.

More hostile

“We’ve identified changes in the environment in which the deep tropics have become more hostile to the formation and intensification of tropical cyclones, and the higher latitudes have become less hostile,” Dr Kossin said. “This seems to be driving the poleward migration of storm intensity.”

Kerry Emanuel, professor of atmospheric science at the Massachusetts Institute of Technology and co-author of the report, said: “The trend is statistically significant at a pretty high level.”

Another of the report’s authors, Gabriel Vecchi, also of NOAA, said: “Now we see this clear trend, it is crucial that we understand what caused it – so we can understand what is likely to occur in the years and decades to come.”

There seems to be an ideal ocean surface temperature of between 28°C and 30°C at which tropical cyclones are most likely to happen. As temperate seas begin to warm, the hazard zone widens.

Not prepared

The superstorm Hurricane Sandy, which devastated New York in 2012, slammed into a coast not prepared either for the force of the wind or for the storm surge that washed through the coastal structures.

But storms are capricious, and notoriously hard to map accurately, so the researchers decided that the surest guide to any pattern of migration would be the latitude at the point of maximum intensity.

They identified regional differences, but found that every ocean basin except the northern Indian Ocean had experienced such a change. Changes in vertical wind shear – which plays a role in cyclone formation – may be involved.

The incidence of cyclones in the tropics actually fell between 1982 and 2012. The suspicion is that although tropical cyclones may become more intense in a warmer climate, it may also be harder to generate them. – Climate News Network