30 March 2016, Climate Central, Antarctica at Risk of Runaway Melting, Scientists Discover. The world’s greatest reservoir of ice is verging on a breakdown that could push seas to heights not experienced since prehistoric times, drowning dense coastal neighborhoods during the decades ahead, new computer models have shown. A pair of researchers developed the models to help them understand high sea levels during previous eras of warmer temperatures. Then they ran simulations using those models and found that rising levels of greenhouse gases could trigger runaway Antarctic melting that alone could push sea levels up by more than three feet by century’s end. The same models showed that Antarctica’s ice sheet would remain largely intact if the most ambitious goals of last year’s Paris agreement on climate change are achieved. The new findings were published Wednesday in the journal Nature, helping to fill yawning gaps in earlier projections of sea level rise. The models were produced by a collaboration between two scientists that began in the 1990s. In those models, rising air temperatures in Antarctica caused meltwater to seep into cracks in floating shelves of ice, disintegrating them and exposing sheer cliffs that collapsed under their own weight into the Southern Ocean. Similar effects of warming are already being observed in Greenland and in some parts of Antarctica, as greenhouse gas pollution from fossil fuels, farming and deforestation warms the air. Last year was the hottest on record, easily surpassing a record set one year earlier. The ice sheets are also being melted from beneath by warming ocean temperatures. “Sea level has risen a lot — 10 to 20 meters — in warm periods in the past, and our ice sheet models couldn’t make the Antarctic ice sheet retreat enough to explain that,” said David Pollard, a Penn State climate scientist who produced Wednesday’s study with UMass professor Robert DeConto. “We were looking for new mechanisms that could make the ice more vulnerable to climate warming to explain past sea level rise,” Pollard said. Read More here
Category Archives: Antarctica
14 March 2016, The Conversation, Tipping point: how we predict when Antarctica’s melting ice sheets will flood the seas. Antarctica is already feeling the heat of climate change, with rapid melting and retreat of glaciers over recent decades. Ice mass loss from Antarctica and Greenland contributes about 20% to the current rate of global sea level rise. This ice loss is projected to increase over the coming century. A recent article on The Conversation raised the concept of “climate tipping points”: thresholds in the climate system that, once breached, lead to substantial and irreversible change. Such a climate tipping point may occur as a result of the increasingly rapid decline of the Antarctic ice sheets, leading to a rapid rise in sea levels. But what is this threshold? And when will we reach it? What does the tipping point look like? The Antarctic ice sheet is a large mass of ice, up to 4 km thick in some places, and is grounded on bedrock. Ice generally flows from the interior of the continent towards the margins, speeding up as it goes. Where the ice sheet meets the ocean, large sections of connected ice – ice shelves – begin to float. These eventually melt from the base or calve off as icebergs. The whole sheet is replenished by accumulating snowfall. Floating ice shelves act like a cork in a wine bottle, slowing down the ice sheet as it flows towards the oceans. If ice shelves are removed from the system, the ice sheet will rapidly accelerate towards the ocean, bringing about further ice mass loss. A tipping point occurs if too much of the ice shelf is lost. In some glaciers, this may spark irreversible retreat. Read More here
14 March 2016, Nature Geoscience, Impacts of warm water on Antarctic ice shelf stability through basal channel formation. Antarctica’s ice shelves provide resistance to the flow of grounded ice towards the ocean. If this resistance is decreased as a result of ice shelf thinning or disintegration.1 , acceleration of grounded ice can occur, increasing rates of sea-level rise. Loss of ice shelf mass is accelerating, especially in West Antarctica, where warm seawater is reaching ocean cavities beneath ice shelves 2 . Here we use satellite imagery, airborne ice-penetrating radar and satellite laser altimetry spanning the period from 2002 to 2014 to map extensive basal channels in the ice shelves surrounding Antarctica. The highest density of basal channels is found in West Antarctic ice shelves. Within the channels, warm water flows northwards, eroding the ice shelf base and driving channel evolution on annual to decadal timescales. Our observations show that basal channels are associated with the development of new zones of crevassing, suggesting that these channels may cause ice fracture. We conclude that basal channels can form and grow quickly as a result of warm ocean water intrusion, and that they can structurally weaken ice shelves, potentially leading to rapid ice shelf loss in some areas. Read More here. See also Washington Post article here
10 March 2016, Climate News Network, Antarctic techno-fix cannot slow rising seas. Pumping seawater onto the Antarctic landmass to form ice and stop sea levels rising stands little chance of success, scientists say. Sea level rise is likely to be a problem too big to handle. Geoengineers will not be able to magic away the rising tides, according to new research. In particular, they will not be able to pump water from the sea and store it as ice on the continent of Antarctica. That is because, unless they pump it enormous distances, that will only accelerate the flow of the glaciers and it will all end up back in the sea again, a study in the journal Earth System Dynamics says. Geoengineering is sometimes produced as the high-technology solution to the environmental problems of climate change: if humans don’t change their ways and start reducing greenhouse gas emissions, say the proponents of technofix, human ingenuity will no doubt devise a different answer. But, repeatedly, closer examination has made such solutions ever less plausible. Scientists have dismissed the idea that the melting of the Arctic can be reversed, have only tentatively conceded that technology could dampen the force of a hurricane, and have found that – instead of cooling the Earth – attempts to control climate change could either make things worse or seriously disrupt rainfall patterns. On balance, scientists believe that most of the big geo-engineering ideas won’t work. Deep freeze And now a team from the Potsdam Institute for Climate Impact Research has poured cold water on the idea of pouring cold water onto the ice cap. The idea is a simple one. Are sea levels rising 3mm a year because the world is warming? Then pump the sea high onto the Antarctic landmass where it will freeze and stay frozen for a millennium. But to be sure of that, say the Potsdam team, at least 80% of the water would have to be pumped 700 km inland. That would take more than 7% of the annual global primary energy supply just to balance the current rate of sea level rise.But even in a world recently committed to a warming of less than 2°C, the seas are going to go on rising. Sea levels could rise at least 40cms by the end of the century – or possibly 130cms, with devastating consequences for low-lying coastlines: rich megacities might be able to build defences, but the poorest communities would be swept away. Read More here