(Also see “Manhattan-Size Ice Island Cracks in Half.”)

The crevasse stretches 19 miles (30 kilometers) long and up to 260 feet (80 meters) wide, as shown in a picture taken by NASA’s Terra satellite in October and featured this week as a NASA Image of the Day.

Snaking across the floating tongue of the Pine Island Glacier in West Antarctica, the crack is expected to create an iceberg 350 square miles (907 square kilometers)—versus 303 square miles (785 square kilometers) for Manhattan, Brooklyn, Queens, Staten Island, and the Bronx combined, according to NASA.

As for when the iceberg might shove off, “that is very difficult to predict,” said oceanographer Eric Rignot of NASA’s Jet Propulsion Laboratory, “but in the coming months for sure.”

Glacier “Contributing Most to Sea Level”

Usually there’s nothing extraordinary about a glacier calving, said glaciologist Ted Scambos of the National Snow and Ice Data Center (NSIDC) in Boulder, Colorado.

Glaciers that flow into the sea, like the Pine Island Glacier, go through a normal cycle in which the floating section grows, stresses mount, and an iceberg breaks off, Scambos said.

“That is nothing unusual in most cases.”

But when the pattern deviates, glaciologists take notice. In this case, the crack is forming significantly farther “upstream” than has previously been the case. That “signifies that there are changes in the ice,” he said.

When “that point of rifting starts to climb upstream, generally you see some acceleration of the glacier.” That means that the ice will flow into the ocean at a faster rate, contributing even more to sea level rise.

(Related: “Hundreds of Glaciers Melting Faster in Antarctica.”)

 Such an acceleration is of particular concern at the Pine Island Glacier, because, among Antarctic glaciers, it’s “the one that’s contributing the most to sea level rise.”

In fact, he said, ice flows from that glacier alone account for a quarter to a third of Antarctica’s total contribution to sea level rise.

“It’s moving at about three kilometers [almost two miles] per year,” Scambos said. And, he noted, “it’s been accelerating quite a bit.”

(Pictures: Antarctica Warming.)

Cracking Glacier “Really Important”

As far as sea levels are concerned, changes in the Pine Island Glacier and other West Antarctic glaciers are far more important than shifts among the continent’s other glaciers, such as East Antarctica’s Mertz Glacier—despite Mertz’s much publicized release of a Luxembourg-size iceberg in early 2010.

That’s because the “Luxembourg” iceberg came from a glacial ice tongue that had just been “sitting there,” said oceanographer Doug Martinson of Columbia University’s Lamont-Doherty Earth Observatory.

By contrast, “West Antarctica has ice streams, of which Pine Island is one. Those are fast-flowing streams of ice,” said Martinson, who specializes in polar oceans.

When ice breaks off the Pine Island Glacier, he said, more ice can flow in faster from the mountains above—ice that will eventually wind up contributing to sea level rise.

“This glacier,” NSIDC’s Scambos added, “is really important.”

Source National Geographic

The following YouTube presentation is taken from the soon to be release book ‘Letters from 2030’
Leon Tolstoy once wrote – People were not inclined to take their situation with any degree of seriousness: on the contrary they became even more frivolous, as is always the case with people who see a great catastrophe approaching … they argue that it is too depressing to think of the danger since it is not in man’s power to foresee everything and avert the general march of events, and it is better therefore to shut one’s eyes to the disagreeable until it actually comes, and to think instead of what is pleasant.

The Reality is a future we must change for all who will inherit the future we have left them, my children, your children and theirs.

The Reality is that those with vested interests to protect (big oil and coal; amongst others) have the status quo to protect. They have successfully done this with misinformation about climate change, as others have done in the past. :– Smoking is not addictive or a heath hazard!

The Climate Reality Project is to raise awareness of a need for collective understanding that the single (multiple) ‘extreme weather events’ around the world over recent times are related to a change in climate, directly resulting from the pollution of our atmosphere by the burning of once safely stored carbon (fossil fuels ) along with the increase of other greenhouse gases resulting from positive feedbacks linked with these emissions. We have entered unknown and very dangerous territory with our giant chemical experiment with the atmosphere.

Join with us now on this global action day to ask those still sitting on the inactive fence of comfortable complacency, to demand action from our policy makers, to move to a future, safe, for those who will inherit what we are leaving behind; my children and yours.

Join us in the live discussion

Free desktop streaming application by Ustream

The map, along with an associated animation (below) developed by NASA, reveals that ice is flowing fastest in coastal ice shelves and their tributaries, shown in this illustration in bright purple and blue. Though it’s ice that’s moving, not water, “you can imagine it like a river system,” says Bernd Scheuchl, one of the map’s creators. The fastest ice flows out to sea at a rate of a few kilometers a year. Pine Island and Thwaites Glaciers on the west coast are the most active.

The team was surprised by how far inland they found fast-moving ice, Scheuchl says. So, if Antarctica loses a great deal of its coastal ice to climate change in the coming decades, large quantities of interior ice could follow. “That’s critical knowledge for predicting future sea level rise,” NASA polar scientist Thomas Wagner said in a prepared statement.

To create this view of Antarctic ice flow, the UC Irvine researchers relied on data from satellites operated by Canada, Japan and the European Space Agency. Flow was tracked from 2007 to 2009 during a period of intense scientific monitoring of Earth’s poles that researchers all over the world had agreed to do. A report on the map was published online August 18 in Science.

Source Scientific America

Despite America’s intense political polarization over climate change, the scientific measurement of global warming is not in dispute. Since 1900, the earth as a whole has warmed by 1.4 degrees Fahrenheit, an empirical fact that has become an official statistic of the National Oceanic and Atmospheric Administration.

It is a seemingly minuscule and barely perceptible increase of average temperature, but spread over the entire surface of the earth that extra energy accumulates into an enormous force. Just what the impact is on the climate system is something that scientists are only now beginning to understand.

“Seemingly very small changes can have very big implications,” said Gerald Meehl, a senior scientist at the National Center for Atmospheric Research (NCAR) in Boulder, Colo.

The 1.4 degree rise in average temperature means the entire surface of earth’s 500 million square kilometers has become home to between 250 and 500 million megawatts of energy that used to escape the planet’s atmospheric shell into space. That’s an extra 0.5 to one watt, or roughly one Christmas light bulb’s worth of heat, falling on every square meter of land and sea.

“It might seem small, but it actually is very significant when you look at earth’s history,” said Pushker Kharecha, a climate scientist at the NASA Goddard Institute for Space Studies and The Earth Institute at Columbia University. For the climate to be relatively stable, he said, the energy balance must remain “within a small fraction of a watt [per square meter].”

“No question about it, it’s a lot of energy,” said Warren Washington, a senior scientist at NCAR.

In a year’s time, this energy imbalance is roughly equivalent to 15 to 30 times the global energy consumption of 2007, or to the amount of power generated by 250,000 to half a million large coal-fired power plants.

Natural fluctuations in solar output are “somewhat” responsible, Kharecha said. But “when we look at the interdecadal trends, it’s very clear that the human force is what’s causing the vast majority of change in recent decades.”

“What humans are doing is creating an imbalance,” said Jeff Kiehl, a senior scientist in the climate modeling section of NCAR. “We’re … putting more greenhouse gases into the atmosphere, which limits the amount of flow of infrared radiation [heat] going back out into space.”

As a result, the planet as a whole is heating up, Kiehl said, because “[earth's] response is to warm up or cool down in response to any energy imbalance.”

“It’s a fundamental law of physics that energy is conserved. It can’t be created or destroyed. It can be transferred or transformed,” he continued. “If we’re trapping infrared radiation on this planet that energy has to go somewhere. It can’t just disappear.”

Extra Energy and Extreme Weather

So where exactly does all the extra energy go, and how does it influence earth’s complex weather phenomena? “Some goes into the oceans and some as latent heat in the atmosphere, and that energy is available to be transformed into things like storms,” Kiehl explained.

Scientists say most of the extra energy ends up warming the world’s seas because of water’s enormous capacity to trap heat. The rest goes into the ground or toward raising temperatures in the atmosphere. That captured heat can melt ice caps and evaporate water, creating additional water vapor, a greenhouse gas.

The extra moisture can also power climatic extremes, including severe thunderstorms.

Consistent with this picture of rising heat and moisture in the atmosphere, Kiehl said, is that the “frequency and intensity of extreme weather events should also increase,” including record heat waves, floods, blizzards and droughts.

“The big question is, is that what we’re seeing today?”

Climate scientists say the lack of uniform and lengthy historical data and the complexity of the climate system makes it difficult to draw a cause-and-effect relationship between the extra heat and extreme weather events, which seem to be occurring with alarming frequency in recent years.

“There’s a lot of complexity,” said Kevin Trenberth, senior scientist at NCAR. “You can’t understand the [climate] system with simple links.”

But amid the current wild extremes the question is growing in importance. A quick look at some recent devastating weather events reveals why:

Across the U.S. Midwest and East Coast, temperatures climbed to over 100 degrees Fahrenheit this month. According to NOAA’s National Weather Service, 1,149 daily high maximum temperature records were broken between July 1 and July 19.

July 2010 was Russia’s hottest July in at least 130 years. Temperatures reached over 100 degrees Fahrenheit in Moscow as wildfires burned hundreds of thousands of acres of forest and peatlands. The fires destroyed about a third of Russia’s cultivable land, leading to a temporary ban on wheat exports that sent food prices soaring.

The ongoing drought in East Africa is the worst to strike the region in six decades. Somalia has been particularly hard-hit as crop failure exacerbates a humanitarian crisis caused by military conflict and years of famine. The UN estimates that 10 million people are threatened by starvation.

In May 2011, the combination of heavy rains and snowmelt from a stormy winter fueled the worst floods to hit the Mississippi River Basin since at least 1937, prompting the Army Corps of Engineers to blow up levees to save cities from the surging waters.

Last year in Australia heavy precipitation triggered mass flooding from Dec. 2010 to Jan. 2011. In Queensland, flooding covered an area equal to the size of France and Germany. Thousands were evacuated from their homes, with total damage estimated to be $20 billion.

Not So Simple

“These things are consistent with the kind of changes we expect to see [from global warming],” said Kathleen Miller, a NCAR scientist who studies natural resource systems and the impact of climate change on societies. But she was wary of identifying global warming’s role.

“Anything you see is some combination of natural internal variability and the effects of climate change,” she said. “For any particular event, you can’t clearly separate out what is the primary influence.”

“We’re more certain of some things than others,” said Meehl. “Temperature is the one where there’s the greatest certainty.”

For instance, the United States had twice as many record-high daily temperatures than record lows from 2000-2009 compared to the 1950s, when the two were about equal, according to a study by Meehl.

That same trend is seen in decadal average temperatures, said Washington of NCAR, which “have gone up over time.” Other statistics show “the number of heat waves is increasing and the number of cold waves is decreasing,” he said.

Hurricanes, which get their power from hot humid air over the oceans, are also on the rise in parts of the world. Trenberth says there is a direct causal link with extra atmospheric heat.

“It’s now one degree Fahrenheit warmer and there’s four percent more moisture [over the oceans] than 30 to 40 years ago. That’s the environment in which all storms now develop … [and these are] conditions that tend to make storms more intense.”

In the tropical North Atlantic, said Kharecha, there’s a “strong correlation” between increasing sea surface temperatures and the “frequency and intensity” of hurricanes since the 1950s. But that trend cannot be found in hurricane trends worldwide, and the lack of reliable data before the 1960s — when satellites were first put into use — means more research is needed.

Extremes in rainfall patterns are also likely being affected, data shows. In the U.S., the amount of heavy precipitation events increased 16-20 percent from 1958 to 2007, said Washington, referencing a 2009 report from the U.S. Global Change Research Program.

“The hydrological cycle of the earth is spinning up as we put more energy into the climate system,” said Kiehl.

A Key Metric

With global average temperature expected to rise another 3.6 to 7.2 degrees Fahrenheit over the course of the current century, scientific certainty over just how the extra energy will ripple through the climate system will likely lag behind the occurrence of extreme weather events.

But there remains little doubt among scientists that a planetary energy imbalance is changing the weather system. This, more than rising average temperatures, is perhaps the most important metric for understanding changes to the climate system.

“Temperature is a way to measure the heat, it’s a great metric,” Kharecha said. But energy imbalance is “the most fundamental gauge of the state of the climate system at any given time” and can help provide insight into “how much we must reduce atmospheric greenhouse gas levels to restore the planet’s energy balance.”

Source IBTimes Canada

An irreversible climate “tipping point” could occur within the next 20 years as a result of the release of huge quantities of organic carbon locked away as frozen plant matter in the vast permafrost region of the Arctic, scientists have found.Billions of tons of frozen leaves and roots that have lain undisturbed for thousands of years in the permanently frozen ground of the northern hemisphere are thawing out, with potentially catastrophic implications for climate change, the researchers said.

A study into the speed at which the permafrost is melting suggests that the tipping point will occur between 2020 and 2030 and will mark the point at which the Arctic turns from being a net “sink” for carbon dioxide into an overall source that will accelerate global warming, they said.

The study is the first global investigation of what will happen in a warmer world to the huge amounts of frozen plant matter that has remained undegraded in the soil since it was incorporated into the permafrost about 30,000 years ago.

It also found that by 2200 about two-thirds of the Earth’s permafrost will have melted, releasing an estimated 190 billion tons of carbon dioxide and methane into the air – about half of all the fossil fuel emissions of greenhouse gases since the start of the industrial revolution.

“Our results indicate that, as the Arctic warms up, this frozen carbon will thaw out, allowing microbial decay to resume and releasing carbon into the atmosphere,” said Kevin Schaefer of the US National Snow and Ice Data Centre in Boulder, Colorado.

“Our research shows that the release of carbon from permafrost will result in an irreversible climate tipping point in only 20 years… Once the frozen carbon thaws out and decays, there is no way to put it back into the permafrost,” Dr Schaefer said.

The Arctic has experienced some of the greatest climatic changes in the world over recent decades. Summer sea ice has melted back to record minimums, average temperatures have increased dramatically, and scientists have documented significant melting of the underground permafrost, from Alaska to eastern Siberia.

The rising temperatures have lengthened the growing season of the Arctic summer, which has increased plant growth and the consequent uptake of carbon dioxide. However, by around 2025 this will go into reverse and the thawing permafrost will release more carbon than is being taken up by the tundra growing above it, Dr Schaefer said.

“There are two important messages from this study. The first is that the melting permafrost can release huge amounts of carbon and, secondly, the process is irreversible on a human timescale and will affect our targets for reducing fossil fuel emissions,” he said.

“All our emission reduction strategies are designed to hit a target atmospheric carbon dioxide concentration corresponding to a target climate. If we do not account for carbon released from thawing permafrost, we will overshoot this target concentration and end up with a warmer climate than we want,” Dr Schaefer said.

Permanently frozen ground covers about a quarter of the northern hemisphere and starts about a metre below the surface, extending up to 500 metres. The top three metres contain most of the frozen plant matter, primarily grass roots caught up in the last ice age.

Source Independent UK

Economic recession has failed to curb rising emissions, undermining hope of keeping global warming to safe levels Photograph: Dave Reede/All Canada Photos/Corbis

Greenhouse gas emissions increased by a record amount last year, to the highest carbon output in history, putting hopes of holding global warming to safe levels all but out of reach, according to unpublished estimates from the International Energy Agency.

The shock rise means the goal of preventing a temperature rise of more than 2 degrees Celsius – which scientists say is the threshold for potentially “dangerous climate change” – is likely to be just “a nice Utopia”, according to Fatih Birol, chief economist of the IEA. It also shows the most serious global recession for 80 years has had only a minimal effect on emissions, contrary to some predictions.

Last year, a record 30.6 gigatonnes of carbon dioxide poured into the atmosphere, mainly from burning fossil fuel – a rise of 1.6Gt on 2009, according to estimates from the IEA regarded as the gold standard for emissions data.

“I am very worried. This is the worst news on emissions,” Birol told the Guardian. “It is becoming extremely challenging to remain below 2 degrees. The prospect is getting bleaker. That is what the numbers say.”

Professor Lord Stern of the London School of Economics, the author of the influential Stern Report into the economics of climate change for the Treasury in 2006, warned that if the pattern continued, the results would be dire. “These figures indicate that [emissions] are now close to being back on a ‘business as usual’ path. According to the [Intergovernmental Panel on Climate Change's] projections, such a path … would mean around a 50% chance of a rise in global average temperature of more than 4C by 2100,” he said.

“Such warming would disrupt the lives and livelihoods of hundreds of millions of people across the planet, leading to widespread mass migration and conflict. That is a risk any sane person would seek to drastically reduce.”

Birol said disaster could yet be averted, if governments heed the warning. “If we have bold, decisive and urgent action, very soon, we still have a chance of succeeding,” he said.

The IEA has calculated that if the world is to escape the most damaging effects of global warming, annual energy-related emissions should be no more than 32Gt by 2020. If this year’s emissions rise by as much as they did in 2010, that limit will be exceeded nine years ahead of schedule, making it all but impossible to hold warming to a manageable degree.

Emissions from energy fell slightly between 2008 and 2009, from 29.3Gt to 29Gt, due to the financial crisis. A small rise was predicted for 2010 as economies recovered, but the scale of the increase has shocked the IEA. “I was expecting a rebound, but not such a strong one,” said Birol, who is widely regarded as one of the world’s foremost experts on energy.

John Sauven, the executive director of Greenpeace UK, said time was running out. “This news should shock the world. Yet even now politicians in each of the great powers are eyeing up extraordinary and risky ways to extract the world’s last remaining reserves of fossil fuels – even from under the melting ice of the Arctic. You don’t put out a fire with gasoline. It will now be up to us to stop them.”

Most of the rise – about three-quarters – has come from developing countries, as rapidly emerging economies have weathered the financial crisis and the recession that has gripped most of the developed world.

But he added that, while the emissions data was bad enough news, there were other factors that made it even less likely that the world would meet its greenhouse gas targets.

• About 80% of the power stations likely to be in use in 2020 are either already built or under construction, the IEA found. Most of these are fossil fuel power stations unlikely to be taken out of service early, so they will continue to pour out carbon – possibly into the mid-century. The emissions from these stations amount to about 11.2Gt, out of a total of 13.7Gt from the electricity sector. These “locked-in” emissions mean savings must be found elsewhere.

“It means the room for manoeuvre is shrinking,” warned Birol.

• Another factor that suggests emissions will continue their climb is the crisis in the nuclear power industry. Following the tsunami damage at Fukushima, Japan and Germany have called a halt to their reactor programmes, and other countries are reconsidering nuclear power.

“People may not like nuclear, but it is one of the major technologies for generating electricity without carbon dioxide,” said Birol. The gap left by scaling back the world’s nuclear ambitions is unlikely to be filled entirely by renewable energy, meaning an increased reliance on fossil fuels.

• Added to that, the United Nations-led negotiations on a new global treaty on climate change have stalled. “The significance of climate change in international policy debates is much less pronounced than it was a few years ago,” said Birol.

He urged governments to take action urgently. “This should be a wake-up call. A chance [of staying below 2 degrees] would be if we had a legally binding international agreement or major moves on clean energy technologies, energy efficiency and other technologies.”

Governments are to meet next week in Bonn for the next round of the UN talks, but little progress is expected.

Sir David King, former chief scientific adviser to the UK government, said the global emissions figures showed that the link between rising GDP and rising emissions had not been broken. “The only people who will be surprised by this are people who have not been reading the situation properly,” he said.

Forthcoming research led by Sir David will show the west has only managed to reduce emissions by relying on imports from countries such as China.

Another telling message from the IEA’s estimates is the relatively small effect that the recession – the worst since the 1930s – had on emissions. Initially, the agency had hoped the resulting reduction in emissions could be maintained, helping to give the world a “breathing space” and set countries on a low-carbon path. The new estimates suggest that opportunity may have been missed.

Source Guardian

By then, Perth and the South-West would become solely reliant on water supplied from the already stressed Gnangara Mound aquifer and the Kwinana desalination plant, director Jorg Imberger said.

Even using an optimistic calculation that 35 gigalitres (35 billion litres) of rainwater would flow into the city’s dams – far greater than the 13 gigalitres last year – the dams would run dry.

“(Even) given recycled water, less water use, pumping the surface aquifer at Gnangara Mound a little bit more and hoping for rain, we’ll basically have no water left at the end of summer 2012,” Professor Imberger said.

The comments confer with the national Climate Commissioner’s first report released yesterday, which warns that water availability will be at great risk before the end of the century due to changing rainfall patterns.

WA’s South-West region was already “drying out” and all projections showed no improvement, the report by Professor Will Steffen said.

“Rainfall is the main driver of run-off, which is the direct link to water availability,” the report says.

“Hydrological modelling indicates that water availability will likely decline in south-west Western Australia.”

Perth’s dam capacity is already below 25 per cent and only 10 per cent of that is drinkable.

WA Water Commission figures show the average amount of rainfall flowing into the dams has dramatically declined since 1974:

1911 – 1974 – 338 gigalitres

1974 – 2000 – 117 gigalitres

2001 – 2005 – 92.4 gigalitres

2006 – 2010 – 57.7 gigalitres

“It’s raining less but the reduction into reservoirs has reduced even more because the vegetation is sucking up the rest (due to deforestation),” Professor Imberger said.

“Between 30-40 per cent of that reduction is due to climate change. The remainder is down to land clearing – trees are not (there to) recycle water the way they used to be.”

But a Water Corporation spokesman said it was too early too predict how much water would be left in the dams by early next year.

He said over the past 10 years the dams had averaged 100 billion litres of water per year, although last year only 13 billion litres flowed.

Rainfall flows into the dams had been getting later and later each year but it already started this year.

According to the Bureau of Meteorology, the Perth metropolitan area recorded only 59 per cent of its average annual rainfall last year.

A record hot summer brought no relief and so far this year, less than 50 millimetres of rain has fallen in Perth.

Professor Imberger said the state government’s only option to avoid running out of drinking water was to immediately bring other sources online.

That included expanding use of the Yarragadee aquifer in the South-West, doubling capacity of the second desalination plant at Binningup – due to come online by the end of the year to provide 45 gigalitres of water – to 100 gigalitres, and improving water recycling.

“Of this really serious situation nobody seems to be doing something about it,” Professor Imberger said. “Maybe they’re just hoping all this is going to go away.”

Several WA water experts have recommended tapping further into the Yarragadee aquifer to ease pressure on Gnangara Mound, which stretches from Gingin, north of Perth, to the Swan River.

The south-west aquifer stores about 1000 gigalitres and could provide three times as much drinking water as the Kwinana desalination plant, according to Professor Imberger, but the government has so far resisted using it due to opposition from locals.

Professor Imberger said planting thousands of new trees in south-west WA also would help boost future rainfalls.

The state government did not respond to inquiries about how it was managing Perth’s drinking water supply.

Source WA Today

Futher Reading – Perth’s Water Wars

New University of Washington research shows that rising sea surface temperatures in the area of the Pacific Ocean along the equator and near the International Date Line drive atmospheric circulation that has caused some of the largest shifts in Antarctic climate in recent decades.

The warmer water generates rising air that creates a large wave structure in the atmosphere called a Rossby wave train, which brings warmer temperatures to West Antarctica during winter and spring.

Antarctica is somewhat isolated by the vast Southern Ocean, but the new results “show that it is still affected by climate changes elsewhere on the planet,” said Eric Steig, a UW professor of Earth and space sciences and director of the UW Quaternary Research Center.

Steig is the corresponding author of a paper documenting the findings that is being published April 10 in the journal Nature Geoscience. The lead author is Qinghua Ding, a postdoctoral researcher in the UW Quaternary Research Center. Co-authors are David Battisti, a UW atmospheric sciences professor, and Marcel Küttel, a former UW postdoctoral researcher now working in Switzerland.

The scientists used surface and satellite temperature observations to show a strong statistical connection between warmer temperatures in Antarctica, largely brought by westerly winds associated with high pressure over the Amundsen Sea adjacent to West Antarctica, and sea surface temperatures in the central tropical Pacific Ocean.

They found a strong relationship between central Pacific sea-surface readings and Antarctic temperatures during winter months, June through August. Though not as pronounced, the effect also appeared in the spring months of September through November.

The observed circulation changes are in the form of a series of high- and low-pressure cells that follow an arcing path from the tropical Pacific to West Antarctica. That is characteristic of a textbook Rossby wave train pattern, Ding said, and the same pattern is consistently produced in climate models, at least during winter.

Using observed changes in tropical sea surface temperatures, the researchers found they could account for half to all of the observed winter temperature changes in West Antarctica, depending on which observations are used for comparison.

“This is distinct from El Niño,” Steig said. That climate phenomenon, which affects weather patterns worldwide, primarily influences sea-surface temperatures farther east in the Pacific, nearer to South America. It can be, but isn’t always, associated with strong warming in the central Pacific.

Steig noted that the influence of Rossby waves on West Antarctic climate is not a new idea, but this is the first time such waves have been shown to be associated with long-term changes in Antarctic temperature.

The findings also could have implications for understanding the causes behind the thinning of the West Antarctic Ice Sheet, which contains about 10 percent of all the ice in Antarctica.

Steig noted that the westerly winds created by the high pressure over the Amundsen Sea pushes cold water away from the edge of the ice sheet and out into the open ocean. It is then replaced by warmer water from deeper in the ocean, which is melting the seaward edge of the ice sheet from below.

The work was funded by the National Science Foundation.

Source Science Daily

The original prediction, made in 2007, gained Wieslaw Maslowski’s team a deal of criticism from some of their peers.

Now they are working with a new computer model – compiled partly in response to those criticisms – that produces a “best guess” date of 2016.

Their work was unveiled at the European Geosciences Union (EGU) annual meeting.

The new model is designed to replicate real-world interactions, or “couplings”, between the Arctic ocean, the atmosphere, the sea ice and rivers carrying freshwater into the sea.

“In the past… we were just extrapolating into the future assuming that trends might persist as we’ve seen in recent times,” said Dr Maslowski, who works at Naval Postgraduate School in Monterey, California.

“Now we’re trying to be more systematic, and we’ve developed a regional Arctic climate model that’s very similar to the global climate models participating in Intergovernmental Panel on Climate Change (IPCC) assessments,” he told BBC News.

“We can run a fully coupled model for the past and present and see what our model will predict for the future in terms of the sea ice and the Arctic climate.”

And one of the projections it comes out with is that the summer melt could lead to ice-free Arctic seas by 2016 – “plus or minus three years”.

It does not make predictions about the Greenland ice cap.

Thin evidence

One of the important ingredients of the new model is data on the thickness of ice floating on the sea.

Satellites are increasingly able to detect this, usually by measuring how far the ice sits above the sea surface – which also indicates how far the ice extends beneath.

Inclusion of this data into the team’s modelling was one of the factors causing them to retrench on the 2013 date, which raised eyebrows – and subsequently some criticism – when it emerged at a US science meeting four years ago.

Since the spectacularly pronounced melting of 2007, a greater proportion of the Arctic Ocean has been covered by thin ice that is formed in a single season and is more vulnerable to slight temperature increases than older, thicker ice.

Even taking this into account, the projected date range is earlier than other researchers believe likely.

But one peer – Dr Walt Meier from the US National Snow and Ice Data Center in Boulder, Colorado – said the behaviour of sea ice becomes less predictable as it gets thinner.

“[Maslowski's] is quite a good model, one thing it has is really high resolution, it can capture details that are lost in global climate models,” he said.

“But 2019 is only eight years away; there’s been modelling showing that [likely dates are around] 2040/50, and I’d still lean towards that.

“I’d be very surprised if it’s 2013 – I wouldn’t be totally surprised if it’s 2019.”

Crystal method

The drastic melt of 2007 remains the record loss of ice area in the satellite era, although subsequent years have still been below the long-term average.

But some researchers believe 2010′s melt was equally as notable as 2007′s, given weather conditions that were favourable to the durability of ice.

Although many climate scientists and environmental campaigners are seriously concerned about the fate of the Arctic sea ice, for other parts of society and other arms of government its degradation presents challenges and opportunities.

The Russian and Canadian governments, for example, are looking to the opportunities for mineral exploitation that will arise; while the US military has expressed concern about losing a natural defence around the country’s northern border for part of the year.

“I’m not trying to be alarmist and not trying to say ‘we know the future because we have a crystal ball’,” said Dr Maslowski.

“Basically, we’re trying to make policymakers and people who need to know about climate change in the Arctic realise there is a chance that summer sea ice could be gone by the end of the decade.

“For the national interest, the defence interest, I think it’s important to realise that 2040 is not a crystal ball prediction.”

Source BBC News