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| Sea ice at poles hit record low | |
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| Tweet Topic Started: 17 Feb 2017, 02:46 AM (174 Views) | |
| skibboy | 17 Feb 2017, 02:46 AM Post #1 |
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17 February 2017 Sea ice at poles hit record low for January © AFP/File | Unusually warm temperatures in January contributed to the melting of sea ice in the Arctic, where the average ice cover was 8.6 percent below the 1981?2010 average MIAMI (AFP) - The amount of sea ice at the Earth's poles fell to a record low for January, while the planet's temperatures last month were the third highest in modern times, US government scientists said Thursday. The monthly report by the National Oceanic and Atmospheric Administration is the first of its kind released in 2017, and comes on the heels of the third year in a row for record-setting heat established in 2016. The US federal agency's analysis of global sea surface and land temperatures found that January's temperature was 1.58 Fahrenheit (0.88 Celsius) above the 20th century average of 53.6 F (12 C). "This was the third highest for January in the 1880?2017 record, behind 2016 (highest) and 2007 (second highest)," said the report. Those unusually warm temperatures contributed to the melting of sea ice in the Arctic, where the average ice cover for January was 487,000 square miles (1.26 million square kilometers) -- or 8.6 percent below the 1981?2010 average. "This was the smallest January extent since records began in 1979 and 100,000 square miles smaller than the previous record set in 2016," said the report. In the Antarctic, sea ice extent for January was 432,000 square miles (22.8 percent) below the 1981?2010 average. "This was the smallest January Antarctic sea ice extent since records began in 1979 and 110,000 square miles smaller than the previous record set in 2006," it added. Despite the loss of sea ice, precipitation varied widely across the globe last month. Snow has been falling more heavily than usual in the Northern Hemisphere, where snow cover extent during January reached 890,000 square miles above the 1981 - 2010 average. "This was the sixth largest January Northern Hemisphere snow cover extent in the 51-year period of record," said the study. "The North American snow cover extent was the 13th largest on record, while the Eurasian snow cover extent was the seventh largest." Source: .com
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| skibboy | 18 Feb 2017, 01:44 AM Post #2 |
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Sea ice at record low in Arctic and Antarctic Date 17.02.2017 Author Carla Bleiker Experts across the world are alarmed at how small the area covered by sea ice has become. They are saying the change is unprecedented - and they're calling for action. ![]() (picture-alliance/H. Bäsemann) There is less sea ice today in the Arctic and in the Antarctic than there has ever been before. The area covered by sea ice in the Arctic was at just 13.19 million square kilometers in January 2017. While this may sound big, it's the smallest this area has been since the start of satellite recordings, according to the online "Meereisportal" or sea ice portal, an initiative run by several German research institutions. It's also roughly 1.2 million square kilometers smaller than the long-term average measured from 1981 to 2010. The situation isn't any better in the south, either. There is less sea ice surrounding Antarctica today than there was since reliable records began in 1979. "As of Tuesday, it looks like we hit a new record low in the satellite era," Mark Serreze, the director of the National Snow and Ice Data Center, told US broadcaster CNN on Thursday. The extent to which the ice at the poles is melting is considered an indicator as well as a consequence of global temperature rises. "The annual freeze and thaw of sea ice in the polar regions is like the beating heart of our planet, driving ocean circulation and regulating our climate," Rod Downie, Polar Program Manager at the World Wide Fund for Nature (WWF), wrote in an email to DW. Air temperatures are climbing and so are water temperatures. The ice is melting faster because of that - and it does so later into winter as well. So the period of winter where the water is actually cold enough to freeze is getting shorter, which means the ice floes are getting smaller. But the amount of ice also regulates global temperatures, since water in the seas absorbs heat, whereas ice would reflect it back into space. So with less ice, temperatures are rising even more - it's a vicious circle. The amount of Arctic sea ice was alarmingly low in January, the National Snow and Ice Data Center reported. 2016 was the warmest year on record around the North Pole, with a heat wave hitting in December, and that trend does not appear to be letting up in 2017. "After studying the Arctic and its climate for three and a half decades, I have concluded that what has happened over the last year goes beyond even the extreme," Serreze wrote in an essay for Earth magazine. In Antarctica, long regarded as immune to climate warming, scientists have also monitored changes. Experts across the world are shocked by how much smaller the area covered by sea ice in the Antarctic is today than it was just a few years ago. They are calling for swift action. "The Paris Agreement [which aims to keep the global temperature increase lower than 2 degrees Celsius above pre-Industrial times] has to be implemented as fast as possible," Sybille Klenzendorf, a WWF expert, told DW. "We can still manage to make our goals, but the clock is ticking." WWF's Polar Program Manager Downie stressed that the decline of sea ice in both Arctic and Antarctic will have dire consequences for humans and many other species. "That is bad news for wildlife from blue whales, polar bears and penguins to krill and the many thousands of other species that have evolved to live, on, under or around sea ice," he stated. "And it's bad news for the people of the Arctic and across the world. We need to urgently reduce our carbon emissions and tackle climate change head-on." Source: .com
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| skibboy | 23 Mar 2017, 02:06 AM Post #3 |
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22 March 2017 Sea ice hits new record low at both poles © AFP/File / by Kerry SHERIDAN | Disappearing sea ice comes as the planet marks three years in a row of record-breaking heat, raising new concerns about the accelerating pace of global warming MIAMI (AFP) - The sea ice cover in the Arctic and Antarctic hit new record lows for this time of year, marking the smallest polar ice caps in the 38-year satellite record, US government scientists said Wednesday. In March, the Arctic ice sheet should be at its biggest, but on March 7 the ice cover reached "a record low wintertime maximum extent," said a statement by the US space agency NASA. Data from the NASA-supported National Snow and Ice Data Center (NSIDC) in Boulder, Colorado, also showed that on March 3, "sea ice around Antarctica hit its lowest extent ever recorded by satellites at the end of summer in the Southern Hemisphere." The disappearing sea ice comes as the planet has marked three years in a row of record-breaking heat, raising new concerns about the accelerating pace of global warming and the need to curb burning of fossil fuels which spew heat-trapping greenhouse gasses into the atmosphere. The ice floating in the Arctic Ocean grows and shrinks on a seasonal cycle, reaching its largest size in March and its smallest at the end of the summer melt in September. This year's Arctic maximum spanned 5.57 million square miles (14.42 million square kilometers). That is 37,000 square miles below the previous record low in 2015. When scientists take account of the average sea ice extent for 1981-2010, this year's ice cover is 471,000 square miles smaller. The Arctic sea ice maximum has dropped by an average of 2.8 percent per decade since 1979, NASA said. "We started from a low September minimum extent," said Walt Meier, a sea ice scientist at NASA's Goddard Space Flight Center. "There was a lot of open ocean water and we saw periods of very slow ice growth in late October and into November, because the water had a lot of accumulated heat that had to be dissipated before ice could grow," he added. "The ice formation got a late start and everything lagged behind - it was hard for the sea ice cover to catch up." - Antarctic lows - The ice in the Antarctic also follows a seasonal cycle but its maximum comes in September and its minimum around February. In the Antarctic, this year's record low annual sea ice minimum was 815,000 square miles. That was 71,000 square miles below the previous lowest minimum extent in the satellite record, which occurred in 1997, said NASA. "Since November, daily Antarctic sea ice extent has continuously been at its lowest levels in the satellite record," said the US space agency. For the past two years, however, Antarctica saw record high sea ice extents and decades of moderate sea ice growth. "There's a lot of year-to-year variability in both Arctic and Antarctic sea ice, but overall, until last year, the trends in the Antarctic for every single month were toward more sea ice," said Claire Parkinson, a senior sea ice researcher at NASA Goddard. "Last year was stunningly different, with prominent sea ice decreases in the Antarctic." Scientists still are not sure what this record low in the Antarctic means. "It is tempting to say that the record low we are seeing this year is global warming finally catching up with Antarctica," said Meier. "However, this might just be an extreme case of pushing the envelope of year-to-year variability. We'll need to have several more years of data to be able to say there has been a significant change in the trend." by Kerry SHERIDAN Source: .com
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| skibboy | 3 May 2017, 02:04 AM Post #4 |
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02 May 2017 Ice loss in southwest Antarctica may be slower than thought: study ![]() © AFP/File | Researchers say that, despite the slower rate of melting found in some regions, the continent as a whole is losing mass faster than ever due to climate change WASHINGTON (AFP) - Global warming has caused ice to melt faster than normal in the Antarctic, but a study Tuesday suggested the rate of loss in some areas may be slower than previously thought. Researchers in Britain mapped the change in the speed of ice loss using data from five different satellites, said the report in Geophysical Research Letters, a US scientific journal. After studying changes at more than 30 glaciers since 1992 in Western Palmer Land -- the southwestern corner of the Antarctic Peninsula -- they found ice loss has increased. "Between 1992 and 2016, the flow of most of the region's glaciers increased by between 20 and 30 centimeters (eight to 12 inches) per day, equating to an average 13 percent speedup across the glaciers of Western Palmer Land as a whole," said the report. But the change amounts to just a third of the 45 cubic kilometers (11 cubic miles) of ice loss per year from the sector recently reported by another research team at the University of Bristol. "Although Western Palmer Land holds a lot of ice -- enough to raise global sea levels by 20 centimeters (eight inches) -- its glaciers can't be responsible for a major contribution to sea level rise, because their speed has barely changed over the past 25 years," said study co-author Andrew Shepherd, a professor at the University of Leeds School of Earth and Environment. The greatest speed up in flow and ice loss was seen at glaciers that were grounded at depths more than 300 meters (1,000 feet) below the ocean surface, where warm and salty water can melt ice at the base. Researchers say that, despite the slower rate of melting found in some regions, the continent as a whole is losing mass faster than ever due to climate change. Source: .com
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| skibboy | 11 Jul 2017, 01:09 AM Post #5 |
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Shells record West Antarctic glacier retreat By Jonathan Amos BBC Science Correspondent 9 hours ago ![]() The data used in the study was collected over the last 20 years Scientists are getting a much clearer picture of the retreat of the West Antarctic Ice Sheet over thousands of years, and of the forces driving it. New research indicates that warm waters pulled up from the deep by strong winds sharply undercut glaciers from about 11,000 years ago to 7,500 years ago. This incursion then stopped until it got under way again in the 1940s. The findings are important because they inform our understanding about how the ice may respond in the future. Today, the big glaciers that enter the ocean in a key sector called the Amundsen Sea Embayment are in a rapid withdrawal. These ice streams, such as Pine Island and Thwaites glaciers, are colossal in scale - and their melting has become a significant contributor to global sea-level rise at around 1mm per decade. The glaciers’ grounding lines - the places where they enter the ocean and become buoyant - are heading inland; as are the floating segments, or shelves, they push out in front themselves. Dr Claus-Dieter Hillenbrand, a senior marine geologist at the British Antarctic Survey, explained: "We know today that the ice sheet in the Amundsen Sea is mainly influenced by this warm deep-water upwelling, which is very effectively melting the undersides of the ice shelves and weakening them, and because these shelves buttress the glaciers we therefore get the thinning of the glaciers, the acceleration in the flow speed of the glaciers and the retreat of their grounding lines." Dr Hillenbrand and colleagues have been examining the shells of tiny marine organisms called foraminifera recovered from ocean-floor sediments in the Amundsen Sea Embayment. These shells have chemical "fingerprints" that record the nature of the water in which they were formed. For example, the ratio of different trace metals in the shells says something about how cold or warm the water was. And the different types of carbon incorporated into the shells reveal information about the age of the water. ![]() In Antarctica, the surface waters are "young" and cold; young in the sense that they are in contact with the atmosphere. The deep waters, on the other hand, have not seen the surface in a long time and are therefore considered "old" - but they are relatively warm. Piecing together the distribution and fingerprint pattern of the shells, Dr Hillenbrand's team has been able to show that the warm deep-water would have welled up and spilled across the continental shelf in front of the glaciers to melt their fronts at the end of the last ice age - about 11,000 years ago. This retreat operated until about 7,500 years ago. Independent data has already indicated a coupling between the position of strong westerly winds and upwelling. The further north is the belt of westerlies, the weaker is the upwelling; the further south, the bigger the upwelling. ![]() Pine Island Glacier calves huge tabular icebergs that drift away into the Southern Ocean "We can detect the weakening of the circumpolar deep-water at 7,500 years," said Dr Hillenbrand. "It has been documented through other data that there was a northern shift of these winds then. And around the 1940s, also independent data shows there must have been a southward shift of the belt. So we demonstrate that the circumpolar deep-water upwelling is indeed coupled to the wind system." Some scientists have made the argument that the strengthening westerlies in recent decades can be linked to the ozone hole and the rise in greenhouse gases. The sediments examined in the study are very modern in the geological context, but researchers are also engaged in drilling much deeper materials in the Amundsen Sea Embayment to get a much longer time perspective. For example, scientists would like to get a detailed description of conditions during the last interglacial - the last major warm period on Earth - about 120,000 years ago. Researchers suspect the West Antarctic Ice Sheet at that time became extremely denuded. The big question is whether it could experience a similar withdrawal as the Earth warms as a consequence of rising levels of atmospheric carbon dioxide. "As you know there are some computer models which say a West Antarctic Ice Sheet collapse has potentially already begun," Dr Hillenbrand told BBC News. His team’s study has been published in the journal Nature. Source: .com
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| skibboy | 25 Oct 2017, 10:43 PM Post #6 |
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Arctic Sea Ice May Be Declining Faster Than Expected -Study October 24, 2017 by Reuters ![]() Photo: Shutterstock / Armin Rose CALGARY, Alberta, Oct 24 (Reuters) – Arctic sea ice may be thinning faster than predicted because salty snow on the surface of the ice skews the accuracy of satellite measurements, a new study from the University of Calgary said on Tuesday. The report from the Canadian university’s Cryosphere Climate Research Group published in the academic journal Geophysical Research Letters found satellite estimates for the thickness of seasonal sea ice have been overestimated by up to 25 percent. That means the Arctic Ocean could be ice-free much sooner than some scientific predictions, which forecast sea ice will first disappear completely during summer months between 2040 and 2050, according to lead author Vishnu Nandan. Ice-free summers in the Arctic Ocean would impact global weather patterns by increasing the magnitude and frequency of major storms, and alter the Arctic marine ecosystem, making it harder for animals like polar bears to hunt. There are a wide range of projections as to when Arctic sea ice will start disappearing in summertime as a result of warming global temperatures, and the University of Calgary study calls into question satellite measurements provided so far. “The problem is, microwave measurements from satellites don’t penetrate the salty snow very well, so the satellite is not measuring the proper sea ice freeboard and the satellite readings overestimate the thickness of the ice,” Nandan said. The sea ice freeboard refers to ice that can be seen above sea level and co-researcher John Yackel said, “Our results suggest that snow salinity should be considered in all future estimates on the Arctic seasonal ice freeboard made from satellites.” (Reporting by Nia Williams; editing by Diane Craft) (c) Copyright Thomson Reuters 2017. ![]() Source: |
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| skibboy | 24 Mar 2018, 12:07 AM Post #7 |
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Arctic Ocean Ice Near Record Low for Winter, Boost for Shipping March 23, 2018 by Reuters ![]() Teekay LNG carrier Eduard Toll in the North Sea Route accompanied by an icebreaker in January 2018. Photo: Teekay By Alister Doyle and Timothy Gardner OSLO/WASHINGTON, March 23 (Reuters) – Winter sea ice on the Arctic Ocean covered the second smallest area on record this year, part of a thaw that is opening the region to shipping and oil exploration and may be disrupting weather far to the south, scientists said on Friday. The extent of floating ice likely reached an annual maximum of 14.5 million square kilometers (5.6 million square miles) on March 17, fractionally bigger than a record set in 2017, the U.S. National Snow and Ice Data Center (NSIDC) said. Sea ice around the North Pole freezes to its biggest at the end of the winter in March, and thaws to an annual minimum in September. The ice has shrunk in recent decades in a trend scientists link to man-made climate change. The 2018 winter ice is about a million square kilometers – roughly the size of Egypt or Colombia and bigger than the state of Texas – below the long-term average maximum, NSIDC data show. The center, affiliated with the U.S. National Oceanic and Atmospheric Administration, studies satellite data of the ice going back 39 years. The diminishing ice seems at odds with remarks by President Donald Trump in a television interview in January that “The ice caps were going to melt, they were going to be gone by now. But now they’re setting records.” Until now, most scientific focus has been on a trend of shrinking Arctic sea ice in summer, which is opening shipping routes from the Pacific to the Atlantic and allowing oil and gas exploration even as it harms indigenous peoples and wildlife such as polar bears. Now, “things are increasingly about the winter time,” said Tor Eldevik, a professor at the University of Bergen’s Bjerknes Centre for Climate Research. The winter retreat means ever bigger areas are ice-free year round, especially in the Barents Sea north of Russia and Norway which is becoming more like the Atlantic Ocean, he said. The vast Shtokman natural gas field, north of Russia, is in an area that is now ice-free even in the depths of winter – helping Gazprom if it ever develops the find. The region was ice-bound in winter until the early 1980s, Eldevik said. Shipping company Teekay said a tanker loaded a first cargo of liquefied natural gas at a terminal in Arctic Russia and traveled to France in January 2018 – the first ship to make such a winter voyage without an icebreaker. The retreat may also affect weather far to the south. Researchers suspect that Arctic warmth can disrupt the high altitude jet stream and send brief blasts of frigid air south – such as a “beast from the East” freeze in Europe last month or bitter cold brought by a “bomb cyclone” in the eastern United States. “You could talk about the Arctic having a fever, and boy did the Arctic have a fever this winter, and when it does, Florida feels it,” Jennifer Francis, a professor at Rutgers University’s department of marine and coastal science, told reporters. Florida faced freezing temperatures this year and suffers long-term threats from sea level rise. At the other end of the planet, sea ice around Antarctica recently reached the second smallest for summertime since satellite records began in the 1970s, also behind 2017, the NSIDC said. (Reporting by Alister Doyle Editing by Tom Brown) (c) Copyright Thomson Reuters 2018. ![]() Source: |
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| skibboy | 25 Mar 2018, 12:40 AM Post #8 |
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Arctic Sea Ice Extent Among Lowest On Record Video: https://www.youtube.com/watch?time_continue=3&v=4VvSQZ3FnXQ 2018-03-24 Sea ice in the Arctic grew to its annual maximum extent on March 17 and joined 2015, 2016 and 2017 as the four lowest maximum extents on record, according to scientists at NASA and the National Snow and Ice Data Center. Cover peaked at 5.59 million square miles (14.48 million square kilometers), making it the second lowest maximum on record, at about 23,200 square miles (60,000 square kilometers) larger than the record low maximum reached on March 7, 2017. More significantly from a scientific perspective, the last four years reached nearly equally low maximum extents and continued the decades-long trend of diminishing sea ice in the Arctic. This year’s maximum extent was 448,000 square miles (1.16 million square kilometers) — an area larger than Texas and California combined – below the 1981 to 2010 average maximum extent. Every year, the sea ice cover blanketing the Arctic Ocean and surrounding seas thickens and expands during the fall and winter, reaching its maximum yearly extent sometime between late February and early April. The ice then thins and shrinks during the spring and summer until it reaches its annual minimum extent in September. Arctic sea ice has been declining both during the growing and melting seasons in recent decades. Claire Parkinson, senior climate scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said: “It’s a two-way street: the warming means less ice is going to form and more ice is going to melt, but also, because there’s less ice, less of the sun’s incident solar radiation is reflected off, and this contributes to the warming.” The Arctic has gone through repeated warm episodes this winter, with temperatures climbing more than 40 degrees above average in some regions. The North Pole even experienced temperatures above the freezing point for a few days in February. In mid-March, cooler temperatures and winds pushed out the edge of the sea ice pack and caused a late surge in ice growth that brought the maximum extent closer in line with the past few years. In February, a large area of open water appeared in the sea ice cover north of Greenland, within the multiyear ice pack — the Arctic’s oldest and thickest ice. Most of the opening has refrozen but the new ice is expected to be thinner and more fragile, and a new opening might appear during the melt season. This could make the ice in this region more mobile and prone to exiting the Arctic this summer through either the Fram or Nares straits, ultimately melting in the warmer waters of the Atlantic Ocean. “This old, thicker ice is what we expect to provide stability to the Arctic sea ice system, since we expect that ice not to be as vulnerable to melting out as thinner, younger ice,” said Alek Petty, a sea ice researcher at Goddard. “As ice in the Arctic becomes thinner and more mobile, it increases the likelihood for rapid ice loss in the summer.” Despite the fact that this year’s melt season will begin with a low winter sea ice extent, this doesn’t necessarily mean that there will be another record low summertime extent. “A lot will depend on what the wind and temperature conditions will be in the spring and summer,” Parkinson said. Starting March 22, Operation IceBridge, NASA’s aerial survey of polar ice, is flying over the Arctic Ocean to map the distribution and thickness of sea ice. In the fall, NASA will launch a new satellite mission, the Ice, Cloud and Land Elevation Satellite-2 (ICESat-2), which will continuously monitor how sea ice thickness is changing across the Arctic. Source: .com
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| skibboy | 3 Apr 2018, 01:38 AM Post #9 |
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02 April 2018 2C cap on global warming won't save Arctic sea ice: studies ![]() © GETTY IMAGES NORTH AMERICA/AFP / by Marlowe HOOD | Recent studies have pointed to dwindling sea ice as a likely driver of topsy-turvy winter weather PARIS (AFP) - Even if humanity stops global warming in its tracks at two degrees Celsius, long seen as the guardrail for a climate-safe world, Arctic sea ice will still disappear in some years, scientists have warned. Holding the line at 1.5 C (2.7 degrees Fahrenheit), however, would make a huge difference, according to two separate studies published Monday in the journal Nature Climate Change. In a 2C (3.6F) world, the Arctic Ocean would be ice-free roughly one-in-four years, whereas if warming does not exceed 1.5C, the odds drop to one-in-40, the researchers concluded. "I didn't expect to find that half-a-degree Celsius would make a big difference, but it really does," said Alexandra Jahn, author of one of the studies and an assistant professor at Colorado University in Boulder. The 197-nation Paris climate pact enjoins the world to halt warming at "well under" 2C above mid-19th-century levels, and "pursue efforts" to cap the rise at 1.5C. With one degree of warming so far, Earth has already seen a crescendo of droughts, heatwaves, and storms ramped up by rising seas. The loss of Arctic sea ice is not only a consequence of global warming, but also an accelerant when millions of square kilometres of snow reflecting the Sun's radiation back into space are replaced with dark blue ocean that absorbs it instead. Recent studies have also fingered dwindling sea ice as a likely driver of topsy-turvy winter weather that has seen days when the North Pole is tens of degrees Celsius warmer than Europe and North America. - Ice-free Arctic - In 2017, summer sea ice shrank to 4.64 million square kilometres (1.79 million square miles) in September. That was well above the record low of 3.39 million square kilometres set in 2012, but long-term trends are unmistakable: over the last four decades, minimum sea ice extent has dropped by about 40 percent. The Arctic Ocean is projected to become ice-free in summer -- defined as less than one million square kilometres -- by mid-century unless greenhouse gas emissions are rapidly and deeply reduced. After remaining flat for three years, global CO2 emissions in 2017 went up by 1.4 percent, dashing hopes that they had peaked, the International Energy Agency (IEA) reported last week. Voluntary national pledges made under the Paris pact to cut CO2 emissions, if fulfilled, would yield a 3C world at best. That would transform the Arctic, which has thus far warmed at double the rate of the world as a whole. "Under 3C global average warming, permanent summer ice-free conditions are likely," concluded the second study, led by Michael Sigmond, a researcher at the Canadian Centre for Climate Modelling and Analysis in Victoria. The two modelling studies are among hundreds published since the Paris treaty was inked in 2015 exploring the feasibility and impacts of halting the rise in global temperature at 1.5C, a goal some climate scientists say is likely out of reach. They are also the most recent to conclude that a 2C world will not prevent severe impacts such as mass migrations due to rising seas, regional food and water shortages, and an increase in extreme weather, including heatwaves, droughts and floods. Only a few years ago, the 2C target was upheld as the threshold for avoiding such consequences. by Marlowe HOOD Source: .com
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| skibboy | 4 Apr 2018, 01:16 AM Post #10 |
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Antarctica 'gives ground to the ocean' By Jonathan Amos BBC Science Correspondent 3 April 2018 ![]() A photo of the surface expression of the grounding line on Antarctica's Rutford ice stream. The position is not always so obvious Scientists now have their best view yet of where Antarctica is giving up ground to the ocean as some of its biggest glaciers are eaten away from below by warm water. Researchers using Europe's Cryosat radar spacecraft have traced the movement of grounding lines around the continent. These are the places where the fronts of glaciers that flow from the land into the ocean start to lift and float. The new study reveals an area of seafloor the size of Greater London that was previously in contact with ice is now free of it. The report, which covers the period from 2010 to 2016, is published in the journal Nature Geoscience. "What we're able to do now with Cryosat is put the behaviour of retreating glaciers in a much wider context," said Dr Hannes Konrad from the University of Leeds, UK. "Our method for monitoring grounding lines requires a lot of data but it means you could now basically build a permanent service to monitor the state of the edges of the continent," he told BBC News. ![]() What Cryosat sees: As the grounding line retreats, the elevation of the ice above lowers Although the end product is quite simple, the process of getting to it is quite a complex one. Viewed from above, the position of grounding lines is not always obvious. The glaciers themselves are hundreds of metres thick, and where they begin to float as they come off the continent can be hard to discern in simple satellite images. But there are radar techniques that can find their location by spotting the up and down tidal movement of a glacier's floating ice. This, however, is just a snapshot in time. What Dr Konrad and colleagues have done is use these known positions and then combine the data with knowledge about the shape of the underlying rock bed and changes in the height of the glaciers' surface to track the evolving status of the grounding lines through time. The new study triples the coverage of previous surveys. ![]() The study confirms general trends but with a much wider and more detailed context On the face of it, the results are pretty much as expected. Of the 1,463km² of grounded ice that has been given up, most of it is in well documented areas of West Antarctica where warm ocean water is known to be infiltrating the undersides of glaciers to melt them. Dr Konrad explained: "If you take 25m per year as a threshold, which is sort of the average since the end of the last ice age, and you say anything below this threshold is normal behaviour and anything above it is faster than normal - then in West Antarctica, almost 22% of grounding lines are retreating more rapidly than 25m/yr. "That's a statement we can only make now because we have this wider context." The new data-set confirms other observations that show the mighty Pine Island Glacier, one of the biggest and fast-flowing glaciers on Earth, and whose grounding line has been in retreat since the 1940s, appears now to have stabilised somewhat. The line is currently going backwards by only 40m/yr compared with the roughly 1,000m/yr seen in previous studies. This could suggest that ocean melting at the PIG's base is pausing. Its next-door neighbour, Thwaites Glacier, on the other hand, is seeing an acceleration in the reversal of its grounding line - from 340m/yr to 420m/yr. Thwaites is now the glacier of concern because of its potential large contribution to global sea-level rise. And the UK and American authorities will shortly announce a major joint campaign to go and study this ice stream in detail. ![]() Artwork: Cryosat, with its radar altimeter instrument, was launched to orbit in 2010 Elsewhere on the continent, 10% of marine-terminating glaciers around the Antarctic Peninsula are above the 25m/yr threshold; whereas in East Antarctic, only 3% are. The significant stand-out in the East is Totten Glacier, whose grounding line is retreating at a rate of 154m/yr. Overall, for the entire continent, 10.7% of the grounding line retreated faster than 25m/yr, while 1.9% advanced faster than the threshold. One fascinating number to come out of the study is that grounding lines in general are seen to retreat 110m for every metre of thinning on the fastest flowing glaciers. This relationship will constrain computer models that try to simulate future change on the continent. Leeds co-author Dr Anna Hogg said: "The big improvement here is Cryosat, which gives us continuous, continent-wide coverage, which we simply didn't have with previous radar missions. "Its capabilities have allowed us to build up a picture of retreat rates, especially at the steeply sloping margins of the continent, which is where these changes are taking place. We have eight years of coverage now and it's guaranteed in the future for as long as Cryosat keeps working," she told BBC News. Since conducting the study at Leeds, Dr Konrad has now moved to the Alfred Wegener Institute in Bremerhaven, Germany. Source: .com
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| skibboy | 1 May 2018, 12:14 AM Post #11 |
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Thwaites Glacier: Biggest ever Antarctic field campaign By Jonathan Amos BBC Science Correspondent 30 April 2018 It is going to be one of the biggest projects ever undertaken in Antarctica. UK and US scientists will lead a five-year effort to examine the stability of the mighty Thwaites Glacier. This ice stream in the west of the continent is comparable in size to Britain. It is melting and is currently in rapid retreat, accounting for around 4% of global sea-level rise - an amount that has doubled since the mid-1990s. Researchers want to know if Thwaites could collapse. Were it to do so, its lost ice would push up the oceans by 80cm or more. Some computer models have suggested such an outcome is inevitable if conditions continue as they are - albeit on a timescale of centuries. But these simulations need to be anchored in many more real-world observations, which will now be acquired thanks to the joint initiative announced on Monday. "There is still a question in my view as to whether Thwaites has actually entered an irreversible retreat," said Prof David Vaughan, the director of science at the British Antarctic Survey. "It assumes the melt rates we see today continue into the future and that's not guaranteed. Thwaites is clearly on the verge of an irreversible retreat, but to be sure we need 10 years more data," he told BBC News. The UK's Natural Environment Research Council and the US National Science Foundation are going to deploy about 100 scientists to Thwaites on a series of expeditions. ![]() The International Thwaites Glacier Collaboration (ITGC) is the two nations' biggest cooperative venture on the White Continent for more than 70 years - since the end of a mapping project on the Antarctic Peninsula in the late 1940s. Grants for research totalling £20m have been awarded. Once the costs of transport and resupply to this remotest of regions is factored in, the total value of the ITGC will probably top £40m. Thwaites is a marine-terminating glacier. Snows fall on land and these compact into ice that then flows out to sea. When in balance the quantity of snow at the glacier's head matches the ice lost to the ocean at its front through the calving of icebergs. But Thwaites is out of balance. It has speeded up and is currently flowing at over 4km per year. It is also thinning at a rate of almost 40cm a year. "When we look at the historical satellite record we can see that this thinning started after 2000, spreading inland at a rate of 10-12km/year at its fastest," explained Dr Anna Hogg from Leeds University. "So on Thwaites Glacier, the increase in ice speed has coincided with a period of rapid ice thinning, and grounding line retreat, which suggests that the observed changes may have been caused by warm ocean water reaching the glacier and accelerating ice melt." The grounding line refers to the zone where the glacier enters the sea and lifts up to form a buoyant platform of ice. ![]() If warm ocean bottom-waters are able to get under this shelf, the grounding line can be eroded and the glacier forced backwards even if local air temperatures are sub-zero. Key to this process in the case of Thwaites is that a large portion of the ice stream sits below sea level, with the rock bed sloping back towards the continent. This can produce what scientists refer to as "marine ice sheet instability" - an inherently unstable architecture, which, once knocked, can go into an irreversible decline. "The other process we're concerned about is something called marine ice cliff instability," said Dr Ted Scambos, the principal coordinating investigator on the US side of the project from the National Snow and Ice Data Center. "This is where a tall cliff that might form at the front of the glacier begins to calve - begins to break away - in a runaway fashion. It hasn't been seen yet in this part of Antarctica; it might be present in some parts of the Antarctic Peninsula, but around Greenland seems to be a path to a very rapid retreat of the ice front." ![]() The floating front of the glacier is hundreds of metres thick The ITGC aims to determine how all of this will play out for Thwaites. Its scientists will map the ice stream's every behaviour. They will monitor the way ocean water moves beneath the floating shelf, and drill sediments from under and just in front of the glacier to find out what it did during past warming events on Earth. The work will involve multiple instruments and techniques, including the use of autonomous vehicles. The yellow submarine known as Boaty McBoatface is expected to explore the cavity under the buoyant sections of Thwaites. Seals will also be assisting the research. Prof Karen Heywood from the University of East Anglia, working in tandem with St Andrews University, will be attaching sensors to the heads of the animals. She told BBC News: "The seals dive in the course of their normal life and every time they come to the surface to breathe, the data are transmitted back home. The seals monitor their own environment - where they went, how deep they dived, and how warm the water was they were diving in. At the end of the year, they moult and the tag falls off, so they don't have to live with it forever." Prof Vaughan said that while the UK and America were leading the project, he thought other countries would want to get involved. "Funding from NERC and NSF has set this train in motion, but I fully expect other nations now to join their carriages." Source: .com
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| skibboy | 1 May 2018, 10:56 PM Post #12 |
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U.S. and UK to Study Antarctic Glacier's Risk of Collapse![]() The Thwaites Glacier (IceBridge / NASA) BY MAREX 2018-04-30 The U.S. and the UK are launching a multi-year, $25 million joint research campaign to study the Thwaites Glacier, a giant Antarctic ice sheet that has sped up its motion in recent years. Scientists are concerned that if Thwaites and an adjacent, similar ice sheet were to collapse, it would raise sea levels by up to three feet. The Thwaites Glacier already accounts for about four percent of global sea level rise - an amount that has doubled since the mid-1990s, according to the U.S. National Science Foundation. Several studies have concluded that it is only a matter of time - very roughly, about 200-1000 years - before Thwaites and other nearby glaciers disappear into the sea. “A large sector of the West Antarctic ice sheet has gone into irreversible retreat,” said glaciologist Eric Rignot of the University of California at Irvine, speaking to the New Scientist in 2014. “The only thing that would stop it is a mountain where glaciers would have to climb uphill. We are fairly confident there’s no such hill or mountain.” The newly-announced International Thwaites Glacier Collaboration (ITGC) will gather data to reduce uncertainty about the probability, magnitude and timing of a collapse. "To answer the key questions of how much and how quickly sea level will change requires scientists on the ground with sophisticated equipment collecting the data we need to measure rates of ice-volume or ice-mass change," said William Easterling, NSF's assistant director for geosciences. "The challenges of conducting fieldwork of this scope and scale in such remote locations are enormous. The only practical way for nations to do this is to work collaboratively, each bringing scientific and logistical resources to enable complex and comprehensive field studies." The nearest major research station to the Thwaites Glacier is roughly 900 miles away, so transporting 100 participating scientists to the research site will take a significant joint effort from both nations. The logistics involved could double the cost of the project. Researchers on the ice will rely on aircraft support from U.K. and U.S. research stations, and oceanographers and geophysicists will approach the glacier from the sea aboard research icebreakers. One grant recipient intends to deploy an autonomous UAV, the Autosub Long Range, to explore the underside of the ice sheet from seaward. The collaboration's scientists will begin their first research season in Antarctica in October, establishing a logistical support structure for future work. The collaboration will continue until 2021. Source: .com
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| skibboy | 13 Jun 2018, 11:23 PM Post #13 |
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Antarctica loses three trillion tonnes of ice in 25 years By Jonathan Amos and Victoria Gill Science correspondents 5 hours ago ![]() Artwork: European satellites in particular have an unbroken record going back to 1992 Antarctica is shedding ice at an accelerating rate. Satellites monitoring the state of the White Continent indicate some 200 billion tonnes a year are now being lost to the ocean as a result of melting. This is pushing up global sea levels by 0.6mm annually - a three-fold increase since 2012 when the last such assessment was undertaken. Scientists report the new numbers in the journal Nature. Governments will need to take account of the information and its accelerating trend as they plan future defences to protect low-lying coastal communities. The researchers say the losses are occurring predominantly in the West of the continent, where warm waters are getting under and melting the fronts of glaciers that terminate in the ocean. "We can't say when it started - we didn't collect measurements in the sea back then," explained Prof Andrew Shepherd, who leads the Ice sheet Mass Balance Inter-comparison Exercise (Imbie). "But what we can say is that it's too warm for Antarctica today. It's about half a degree Celsius warmer than the continent can withstand and it's melting about five metres of ice from its base each year, and that's what's triggering the sea-level contribution that we're seeing," he told BBC News. Space agencies have been flying satellites over Antarctica since the early 1990s. Europe, in particular, has an unbroken observation record going back to 1992. These spacecraft can tell how much ice is present by measuring changes in the height of the ice sheet and the speed at which it moves towards the sea. Specific missions also have the ability to weigh the ice sheet by sensing changes in the pull of gravity as they pass overhead. Imbie's job has been to condense all this information into a single narrative that best describes what is happening on the White Continent. Glaciologists usually talk of three distinct regions because they behave slightly differently from each other. In West Antarctica, which is dominated by those marine-terminating glaciers, the assessed losses have climbed from 53 billion to 159 billion tonnes per year over the full period from 1992 to 2017. On the Antarctic Peninsula, the finger of land that points up to South America, the losses have risen from seven billion to 33 billion tonnes annually. This is largely, say scientists, because the floating ice platforms sitting in front of some glaciers have collapsed, allowing the ice behind to flow faster. East Antarctica, the greater part of the continent, is the only region to have shown some growth. Much of this region essentially sits out of the ocean and collects its snows over time and is not subject to the same melting forces seen elsewhere. But the gains are likely quite small, running at about five billion tonnes per year. And the Imbie team stresses that the growth cannot counterbalance what is happening in the West and on the Peninsula. Indeed, it is probable that an unusually big dump of snow in the East just before the last assessment in 2012 made Antarctica as a whole look less negative than the reality. Globally, sea levels are rising by about 3mm a year. This figure is driven by several factors, including the expansion of the oceans as they warm. But what is clear from the latest Imbie assessment is that Antarctica is becoming a significant player. "A three-fold increase now puts Antarctica in the frame as one of the largest contributors to sea-level rise," said Prof Shepherd, who is affiliated to Leeds University, UK. "The last time we looked at the polar ice sheets, Greenland was the dominant contributor. That's no longer the case." In total, Antarctica has shed some 2.7 trillion tonnes of ice since 1992, corresponding to an increase in global sea level of more than 7.5mm. The latest edition of the journal Nature has a number of studies looking at the state of the continent and how it might change in a warming world. One of these papers, led by US and German scientists, examines the possible reaction of the bedrock as the great mass of ice above it thins. It should lift up - something scientists call isostatic readjustment. New evidence suggests where this process has occurred in the past, it can actually constrain ice losses - as the land rises, it snags on the floating fronts of marine-terminating glaciers. "It's like applying the brakes on a bike," said Dr Pippa Whitehouse from Durham University. "Friction on the bottom of the ice, which was floating but has now grounded again, slows everything and changes the whole dynamic upstream. We do think the rebound (in the future) will be fast, but not fast enough to stop the retreat we've kicked off with today's warming. "Ocean warming is going to make the ice too thin for this process to help." In Imbie's last assessment, the contribution of Antarctica to global sea-levels was considered to be tracking at the lower end of the projections that computer simulations had made of the possible height of the oceans at the end of the century. The new assessment sees the contribution track the upper end of these projections. "At the moment, we have projections going through to 2100, which is sort of on a lifetime of what we can envisage, and actually the sea-level rise we will see is 50/60cm," said Dr Whitehouse. "And that is not only going to impact people who live close to the coast, but actually when we have storms - the repeat time of major storms and flooding events is going to be exacerbated," she told BBC News. Source: bbc.com
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