2617. Antarctica Is Beginning toTurn Green Due to Global Warming

By Chris Mooney, The Washington Post, May 18, 2017

Researchers in Antarctica have discovered rapidly growing banks of mosses on the ice continent’s northern peninsula, providing striking evidence of climate change in the coldest and most remote parts of the planet.

Amid the warming of the last 50 years, the scientists found two different species of mosses undergoing the equivalent of growth spurts, with mosses that once grew less than a millimeter per year now growing over 3 millimeters per year on average.

“People will think of Antarctica quite rightly as a very icy place, but our work shows that parts of it are green, and are likely to be getting greener,” said Matthew Amesbury, a researcher with the University of Exeter in the United Kingdom and lead author of the new study. “Even these relatively remote ecosystems, that people might think are relatively untouched by humankind, are showing the effects of human-induced climate change.”

The study was published Thursday in Current Biology, by Amesbury and colleagues with the University of Cambridge, the British Antarctic Survey and the University of Durham.

Less than 1 percent of present-day Antarctica features plant life. But in parts of the Peninsula, Antarctic mosses grow on frozen ground that partly thaws in the summer — when only about the first foot of soil ever thaws.

The surface mosses build up a thin layer in the summer, then freeze over in winter. As layer builds on top of layer, older mosses subside below the frozen ground, where they are remarkably well preserved due to the temperatures.

Amesbury said that made them “a record of changes over time.”

Soil samples from a 400-mile area along the northern part of the Antarctic Peninsula found dramatic changes in growth patterns going back 150 years.

The Antarctic peninsula has been a site of rapid warming, with more days a year where temperatures rise above freezing. The consequence, the study found, was a four- to five-fold increase in the amount of moss growth in the most recent part of the record.

“This is another indicator that Antarctica is moving backward in geologic time — which makes sense, considering atmospheric CO2 levels have already risen to levels that the planet hasn’t seen since the Pliocene, 3 million years ago, when the Antarctic ice sheet was smaller, and sea levels were higher,” said Rob DeConto, a glaciologist at the University of Massachusetts, Amherst, who was not involved in the study but reviewed it for The Washington Post.

“If greenhouse gas emissions continue unchecked, Antarctica will head even further back in geologic time…perhaps the peninsula will even become forested again someday like it was during the greenhouse climates of the Cretaceous and Eocene, when the continent was ice free,” DeConto continued by email.

The authors agree the currently observed changes are probably just the beginning. “These changes, combined with increased ice-free land areas from glacier retreat, will drive large-scale alteration to the biological functioning, appearance, and landscape of the [Antarctic peninsula] over the rest of the 21st century and beyond,” they wrote.

The moss growth is still modest compared to what’s happening in the Arctic, where a large-scale greening trend has even been captured by satellite. In the Arctic, there’s now so much plant growth that some scientists are hoping it will at least partially offset the loss of carbon from thawing permafrost beneath those plants.

Those days are probably very far off for the Antarctic, but it’s clear the continent used to be a very different landscape.

“We’re starting back on a journey towards that sort of environment,” said Amesbury. “Certainly, Antarctica has not always been the ice place it has been now on very long timescales.”

2254. Climate Model Predicts West Antarctic Ice Sheet Could Melt Rapidly

By Justin Gillis, The New York Times, March 30, 2016

For half a century, climate scientists have seen the West Antarctic ice sheet, a remnant of the last ice age, as a sword of Damocles hanging over human civilization.

The great ice sheet, larger than Mexico, is thought to be potentially vulnerable to disintegration from a relatively small amount of global warming, and capable of raising the sea level by 12 feet or more should it break up. But researchers long assumed the worst effects would take hundreds — if not thousands — of years to occur.

Now, new research suggests the disaster scenario could play out much sooner.

Continued high emissions of heat-trapping gases could launch a disintegration of the ice sheet within decades, according to a study published Wednesday, heaving enough water into the ocean to raise the sea level as much as three feet by the end of this century.

With ice melting in other regions, too, the total rise of the sea could reach five or six feet by 2100, the researchers found. That is roughly twice the increase reported as a plausible worst-case scenario by a United Nations panel just three years ago, and so high it would likely provoke a profound crisis within the lifetimes of children being born today.

Under the Ice Sheet

The vast West Antarctic ice sheet sits on bedrock that dips thousands of feet below sea level. New computer simulations suggest that the warming atmosphere and ocean could attack the ice sheet from above and below, causing sea levels to rise much faster than previously thought.

The situation would grow far worse beyond 2100, the researchers found, with the rise of the sea exceeding a pace of a foot per decade by the middle of the 22nd century. 

Scientists had documented such rates of increase in the geologic past, when far larger ice sheets were collapsing, but most of them had long assumed it would be impossible to reach rates so extreme with the smaller ice sheets of today.

“We are not saying this is definitely going to happen,” said David Pollard, a researcher at Pennsylvania State University and a co-author of the new paper. “But I think we are pointing out that there’s a danger, and it should receive a lot more attention.”

The long-term effect would likely be to drown the world’s coastlines, including many of its great cities.

New York City is nearly 400 years old; in the worst-case scenario conjured by the research, its chances of surviving another 400 years in anything like its present form would appear to be remote. Miami, New Orleans, London, Venice, Shanghai, Hong Kong and Sydney, Australia, are all just as vulnerable as New York, or more so.

In principle, coastal defenses could be built to protect the densest cities, but experts believe it will be impossible to do that along all 95,000 miles of the American coastline, meaning that immense areas will most likely have to be abandoned to the rising sea.

The new research, published by the journal Nature, is based on improvements in a computerized model of Antarctica and its complex landscape of rocks and glaciers, meant to capture factors newly recognized as imperiling the stability of the ice.

The new version of the model allowed the scientists, for the first time, to reproduce high sea levels of the past, such as a climatic period about 125,000 years ago when the seas rose to levels 20 to 30 feet higher than today.

That gave them greater confidence in the model’s ability to project the future sea level, though they acknowledged that they do not yet have an answer that could be called definitive.

“You could think of all sorts of ways that we might duck this one,” said Richard B. Alley, a leading expert on glacial ice at Pennsylvania State University. “I’m hopeful that will happen. But given what we know, I don’t think we can tell people that we’re confident of that.”

Dr. Alley was not an author of the new paper, though it is based in part on his ideas about the stability of glacial ice. Several other scientists not involved in the paper described it as significant, with some of them characterizing it as a milestone in the analysis of huge ice sheets and the risks they pose in a warming world.

But those same scientists emphasized that it was a single paper, and unlikely to be the last word on the fate of West Antarctica. The effort to include the newly recognized factors imperiling the ice is still crude, with years of work likely needed to improve the models.

Peter U. Clark of Oregon State University helped lead the last effort by a United Nations panel to assess the risks of sea level rise; he was not involved in the new paper. He emphasized that the research, like much previous work, highlighted the urgency of bringing emissions of carbon dioxide and other greenhouse gases under control.

Dr. Clark described the new work as “a really important paper that adds to the growing recognition that in the absence of rapid and strong mitigation of carbon emissions, we are in store for a large sea level rise at rates that may be even faster than has been considered.”

It was his panel that had estimated an upper limit of three feet or so on the likely sea level rise in the 21st century, while specifically warning that a better understanding of the vulnerability of Antarctic ice could change that estimate.

The new research is the work of two scientists who have been at the forefront of ice-sheet modeling for years. They are Robert M. DeConto of the University of Massachusetts, Amherst, and Dr. Pollard, who is a colleague of Dr. Alley’s at Penn State.

In a lengthy interview on Monday, Dr. DeConto recounted years of frustration. The computer program he had built in a long-running collaboration with Dr. Pollard showed increasing sophistication in its ability to explain the behavior of ice sheets, but it had some trouble analyzing the past.

Unless global temperatures were raised to unrealistic levels, the model would not melt enough ice to reproduce the high sea levels known to have occurred in previous periods when either the atmosphere or the ocean was warmer. The ability to reproduce past events is considered a stringent test of the merits of any geological model.

“We knew something was missing,” Dr. DeConto said.

The new idea came from Dr. Alley. He urged his colleagues to consider what would happen as a warming climate attacked huge shelves of floating ice that help to protect and buttress the West Antarctic ice sheet.

Smaller, nearby ice shelves have already started to disintegrate, most spectacularly in 2002, when an ice shelf the size of Rhode Island, the Larsen B shelf, broke apart in two weeks.

The West Antarctic ice sheet sits in a sort of deep bowl that extends far below sea level, and if it loses its protective fringes of floating ice, the result is likely to be the formation of vast, sheer cliffs of ice facing the sea. These will be so high they will become unstable in places, Dr. Alley said in an interview, and the warming atmosphere is likely to encourage melting on their surface in the summer that would weaken them further.

The result, Dr. Alley suspected, might be a rapid shrinkage as the unstable cliffs collapsed into the water. Something like this seems to be happening already at several glaciers, including at least two in Greenland, but on a far smaller scale than may be possible in West Antarctica.

When Dr. DeConto and Dr. Pollard, drawing on prior work by J. N. Bassis and C. C. Walker, devised some equations to capture this “ice-cliff instability,” their model produced striking results. In contrast to many prior attempts, it suddenly had no difficulty recreating the high sea levels of past warm periods.

The obvious next step was to ask the model what might happen if human society continues to warm the planet by pouring huge amounts of greenhouse gases into the atmosphere.

The answer the scientists got is described in their paper in the dry language of science, but it could easily serve as the plot device of a Hollywood disaster movie. They found that West Antarctica, which is already showing disturbing signs of instability, would start to break apart by the 2050s.

Vulnerable parts of the higher, colder ice sheet of East Antarctica would eventually fall apart, too, and the result by the year 2500 would be 43 feet of sea level rise from Antarctica alone, with still more water coming from elsewhere, the computer estimated. In some areas, the shoreline would be likely to move inland by miles.

The paper published Wednesday does contain some good news. A far more stringent effort to limit emissions of greenhouse gases would stand a fairly good chance of saving West Antarctica from collapse, the scientists found. That aspect of their paper contrasts with other recent studies postulating that a gradual disintegration of West Antarctica may have already become unstoppable.

But the recent climate deal negotiated in Paris would not reduce emissions nearly enough to achieve that goal. That deal is to be formally signed by world leaders in a ceremony in New York next month, in a United Nations building that stands directly by the rising water.

2225. Antarctica Could Be headed for Major Meltdown

By  Science Daily, February 23, 2016

Map showing the locations of Antarctica's ice shelves, including Larsen C (in yellow on the top left), the largest ice shelf in the Antarctic Peninsula. (Credit: Ted Scambos, NSIDC).

In the early Miocene Epoch, temperatures were 10 degrees warmer and ocean levels were 50 feet higher -- well above the ground level of modern-day New York, Tokyo and Berlin.

It was more than 16 million years ago, so times were different. But there was one important similarity with the world we live in today: The air contained about the same amount of carbon dioxide. That parallel raises serious concerns about the stability of ice sheets in Antarctica, according to a study published in the Proceedings of the National Academy of Sciences.

All told, Antarctica's glaciers are the size of the United States and Mexico combined, and they contain enough water to raise the world's sea level by 180 feet. And although no humans live permanently in Antarctica, what happens there impacts everyone, said Aradhna Tripati, a geochemist at UCLA's Institute of the Environment and Sustainability who collaborated on the research.

"The ice sheets serve as huge stores of water," Tripati said. "As the ice melts, it gets dumped in the ocean and the sea level rises.”

The study is the latest revelation of ANDRILL, a $20 million research project focused on the South Pole. The effort, now 12 years old, has involved 100 researchers from seven countries. ANDRILL researchers were the first to bore holes through Antarctic ice shelves and sea ice to sample the ocean floor below.

Previous research showed that ice shelves -- the parts of the ice sheets that extend over water -- are vulnerable to even small increases in greenhouse gases. But the new study, which was written by Richard Levy of GNS Science, a New Zealand research organization, was the first to demonstrate that the huge, land-based glaciers are also vulnerable.

David Harwood, a University of Nebraska paleontologist who led the study, said the project's goal was to see what prehistoric environments could tell us about the modern era of climate change.

"We're drilling back into the past to understand the future and how dynamic our planet can be," he said.

To do that, researchers set 90 tons worth of drilling equipment on a floating sea ice in McMurdo Sound, where conditions can be particularly harsh: The average August temperature is minus 23 degrees Fahrenheit, and savage windstorms can occur at a moment's notice. Using a diamond-tipped tubular drill, researchers bored through 24 feet of ice, 1,200 feet of water and 3,300 feet of ocean floor. The rock samples they collected preserve a chronological record of environmental conditions dating back 20 million years.

The samples were sent to Tripati for analysis. As she looked at the sedimentary layers, a story began to emerge. Samples that were formed during warmer times, when the ice shelf was gone or unstable, were tan-colored and rich with fossils. But samples drawn from years when the sea was covered with ice, were mostly rock with fossils from only a few deep sea organisms.

Looking even closer, Tripati examined individual molecules from the samples to determine air and water temperatures at different times in history. Warmer times correlated with higher levels of carbon dioxide in the atmosphere, melting ice shelves and the loss of parts of the East Antarctic ice sheet.

According to Tripati, scientists are seeing early signs of the same conditions today.

"If carbon dioxide is sustained at current levels, we run the risk of Antarctic ice shelf disappearance," she said.

The ice shelves are critical because they act like a cork in a Champagne bottle, holding back the huge, land-based flows of glacial ice on the Antarctic continent, Tripati said. But they are particularly sensitive to temperature changes. Just a few degrees of increased warmth can make them disappear because they are warmed by both the air and the sea.

And disappearing ice shelves lead to even more warming because of something called the albedo effect: Light-colored ice reflects the sun's radiation away from Earth. After it melts, the darker-colored seas absorb more radiation and more heat.

That process could take hundreds of years, but signs of rapid change are already here. In 2002, the Larsen B ice shelf -- which was made up of more than 1,250 square miles of 720-foot-thick ice -- disintegrated into the ocean over the course of a month, shocking scientists and observers. Over the past several decades, seven out of 12 ice shelves on the Antarctic Peninsula have collapsed.

"They've just been going like dominoes," Tripati said.

Still, researchers say the PNAS findings offer a glimmer of hope. Policymakers rely on computer models to predict future climate change, and the models now can be refined based on the new information about changes that occurred millions of years ago, Tripati said.

The big question that remains is how fast melting will occur. Harwood said the ANDRILL findings emphasize the fragility of ice shelves and the urgency of taking action on a global scale.

"The models simulate thresholds, points of no return," he said. "It's good for policymakers to know how fast we have to get off this train or turn it in a new direction."

Journal Reference:

1 Richard Levy, David Harwood, Fabio Florindo, Francesca Sangiorgi, Robert Tripati, Hilmar von Eynatten, Edward Gasson, Gerhard Kuhn, Aradhna Tripati, Robert DeConto, Christopher Fielding, Brad Field, Nicholas Golledge, Robert McKay, Timothy Naish, Matthew Olney, David Pollard, Stefan Schouten, Franco Talarico, Sophie Warny, Veronica Willmott, Gary Acton, Kurt Panter, Timothy Paulsen, Marco Taviani. Antarctic ice sheet sensitivity to atmospheric CO2variations in the early to mid-Miocene. Proceedings of the National Academy of Sciences, 2016; 201516030 DOI: 10.1073/pnas.1516030113

2082. Melting Ice in West Antarctica Could Raise Seas by Three Meters, Warns Study

By Agence France-Presse, The Guardian, November 2, 2015

The red area is west Antartica that is melting

A key area of ice in west Antarctica may already be unstable enough to cause global sea levels to rise by three metres of ocean rise, scientists said on Monday.

The study follows research published last year, led by Nasa glaciologist Eric Rignot, warning that ice in the Antarctic had gone into a state of irreversible retreat, that the melting was considered “unstoppable” and could raise sea level by 1.2 metres.

This time, researchers at Germany’s Potsdam Institute for Climate Impact Research pointed to the long-term impacts of the crucial Amundsen Sea sector of west Antarctica, which they said “has most likely been destabilized”.

While previous studies “examined the short-term future evolution of this region, here we take the next step and simulate the long-term evolution of the whole west Antarctic ice sheet,” the authors said in the Proceedings of the National Academy of Sciences.

They used computer models to project the effects of 60 more years of melting at the current rate.

This “would drive the west Antarctic ice sheet past a critical threshold beyond which a complete, long-term disintegration would occur.”

In other words, “the entire marine ice sheet will discharge into the ocean, causing a global sea level rise of about three meters,” the authors wrote.

“If the destabilisation has begun, a three-meter increase in sea level over the next several centuries to millennia may be unavoidable.”

Even just a few decades of ocean warming can unleash a melting spree that lasts for hundreds to thousands of years.

“Once the ice masses get perturbed, which is what is happening today, they respond in a non-linear way: there is a relatively sudden breakdown of stability after a long period during which little change can be found,” said lead author Johannes Feldman.

The authors noted that Antarctica’s situation presents the largest uncertainty in sea level projections for the coming centuries, and that studying the vast region poses many challenges.

And indeed, just days before the PNAS study was released, another scientific paper used Nasa satellite data form 2003 to 2008 to show that Antarctic ice had gained mass, and had packed on enough to exceed the amount lost in other areas.

“We’re essentially in agreement with other studies that show an increase in ice discharge in the Antarctic peninsula and the Thwaites and Pine Island region of west Antarctica,” said a statement by Jay Zwally, a glaciologist with Nasa Goddard Space Flight centre whose study was published on 30 October in the Journal of Glaciology.

“Our main disagreement is for east Antarctica and the interior of west Antarctica – there, we see an ice gain that exceeds the losses in the other areas.”

According to climatologist Michael Mann, who was not involved in either study, the use of older satellite data could be the cause for the disconnect.

“It sounds to me as if the key issue here is that the claims are based on seven-year-old data, and so cannot address the finding that Antarctic ice loss has accelerated in more recent years,” he told AFP.