Before and after shots show disappearing ice over the past 125 years
An series of images by the United States Geological Survey (USGS) has revealed the movement of glaciers in southern Alaska. They reveal how the majority of glaciers have rapidly retreated since the late 19th Century - although a small minority have advanced. The technique - known as repeat photography - helps scientists determine how much a region has changed over time. Slide the images below to see the changing appearance of Alaska's glaciers over time
‹ SLIDE ME › Here the retreat of the Muir Inlet can be seen. On the left, a photograph taken on 13 August 1941 shows a glacier 0.43 miles (0.7km) thick, with large seracs - house-sized chunks of ice - on its face. By 11 August 2005, however, it has completely disappeared from view - seen on the right By analysing the various photographic pairs, scientists can document the evolution of the Alaskan landscape, and see how it is responding to retreating glacier ice - with an interactive map also showing their locations. WHY IS GLACIAL RETREAT BAD?The balance of glaciers and the surrounding environment can drastically affect ecosystems. When glaciers retreat, as many have done since 1850, it can affect the availability of fresh water for irrigation and domestic use. It can also affect animal and plans that depend on melt-water from glaciers, while in the longer term it can cause ocean levels to rise. The increasing rate at which glaciers are retreating is one indication of how global warming is already affecting the planet. One pair of images shows the west shoreline of Muir Inlet, Glacier Bay National Park and Preserve, in Alaska - and the changes that have taken place since 1892. One photograph, taken on 13 August 1941, shows a glacier 0.43 miles (0.7km) thick, with large seracs - house-sized chunks of ice - on its face. By 11 August 2005, however, the glacier has completely disappeared from, the same location, having retreated more than 31 miles (50km). In its place, abundant vegetation is located on the slopes in the photograph. Another pair of images show the retreat of the Reid Glacier between 10 June 1899 and 6 September 2003. The photograph from 1899 is taken towards the northwest and shows the 197-foot (60 metres) high terminus of the retreating glacier. By 104 years later, the glacier has retreated 1.9 miles (3km) and is barely visible in the same field of view. Again, vegetation becomes much more abundant as it retreats.
‹ SLIDE ME › The retreat of Reid Glacier between 10 June 1899 (left) and 6 September 2003 (right) is seen here. The glacier has retreated 1.9 miles (3km) and is barely visible, while more vegetation has begun to grow on the side of the hills
+1 The images of the glaciers in southern Alaska (locations shown here) were compiled by the United States Geological Survey (USGS)
‹ SLIDE ME › This set of images shows the remarkable retreat of the McCarty Glacier between 30 July 1909 (left) and 11 August 2004 (right). The retreat of the glacier here took place over a distance of about 9.8 miles (15km)
‹ SLIDE ME › The first photograph on the left is of the Northwestern Glacier at some point between the mid-1920s and 1940s. A second photograph on the right, taken on 12 August 2005, shows how it has retreated more than 6.2 miles (10km) out of view Another set of images show the stunning retreat of McCarty Glacier between 30 July 1909 and 11 August 2004. The retreat of the glacier here is about 9.8 miles (15km) In a pair of north looking photographs, taken looking west of Harris Bay, another dramatic retreat of ice can be seen. The first photograph is an undated winter to summer view from a postcard, likely from between the mid-1920s and the 1940s. A second photograph, taken on 12 August 2005, shows a startlingly different view of the same location. In the area, the Northwestern Glacier has retreated more than 6.2 miles (10km) out of view. The aptly named Toboggan Glacier, meanwhile, with a gentle slope running down into water, is seen retreating during 103 years between 20 August 1905 and 22 August 2008.
‹ SLIDE ME › The aptly named Toboggan Glacier is seen on the left on 20 August 1905. 103 years later on 22 August 2008, right, it has almost completely disappeared
‹ SLIDE ME › One of the most dramatic pairs of images sees Pederson Glacier, pictured right in the mid-1920s to 1940s, replaced by vegetation including grasses and shrubs by 10 August 2005, seen on the right
‹ SLIDE ME › Not all the glaciers have been on the retreat. Harvard Glacier is seen on the left on 1 July 1909, but by 3 September 2000 - right - it had advanced 0.78 miles (1.25km) One of the most dramatic pairs of images is the Pederson Glacier, seen rapidly from the mid-1920s and 1940s to 10 August 2005. In its place, most of the lake has filled with sediment, and now supports several varieties of grasses, shrubs and aquatic plants. But not all the glaciers have been on the retreat. One, Harvard Glacier, has advanced 0.78 miles (1.25km) between 1 July 1909 and 3 September 2000, seen in a pair of images. Overall, though, the images highlight how the changing climate is having a rapid effect on a variety of ecosystems – and not necessarily for the better.
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| Antarctica in unprecedented detail: Most complete map ever made reveals the continent is shrinking rapidly
A stunning new map that reveals a shrinking Antarctica in unprecedented detail has been made available to the public. The map, which was created by stitching together 3,150 individual satellite images, offers the most detailed view of the continent since 1997. By comparing it to earlier maps of the same regions, scientists have found large chunks of ice in the Antarctic disappearing into the surrounding waters. Scroll down for interactive map
+2 The map, which was created by stitching together 3,150 individual satellite images, offers the most detailed view of the continent since 1997. The Canadian Space Agency, along with the University of Waterloo, collected the images over several months in 2008 aboard the Radarsat-2 satellite The Canadian Space Agency, along with the University of Waterloo, collected the images over several months in 2008 aboard the Radarsat-2 satellite. This satellite was able to cut through cloud cover to get a more accurate reading. Its high-resolution images were then tiled together into a coast-to-coast view of the entire continent. 'These colours in a nutshell represent different physical characteristics of the ice, which the scientist can interpret,' Professor Ellsworth LeDrew, director of the Canadian Cryospheric Information Network, told Emily Gertz at Popular Science. 'It's what is called polarimetric information. It's like looking through a camera's polarising filter. Some wavelengths are up and down and some are side to side.'
+2 This satellite was able to cut through cloud cover to get a more accurate reading. Its high-resolution images were then tiled together into a coast-to-coast view of the entire continent. This image shows a closeup view of Antarctica near the Ronne Ice Shelf ANTARCTIC BEGAN MELTING 5,000 YEARS EARLIER THAN THOUGHTThe Antarctic ice sheet is more unstable than first thought with a recent study suggesting melting began 5,000 years earlier than previously believed. The study was conducted by an international team including researchers from Germany, Canada, Hawaii, Lapland and Australia. It reveals that shrinking of the vast ice sheet accelerated during eight distinct periods between 20,000 and 9,000 years ago. During one period 14,600 years ago, melting glaciers released so many icebergs into the ocean that sea level rose 6.5ft (two metres) in just 100 years. The results provide the first clear evidence for dramatic melting in Antarctic's and reflect predictions for the region's future. It also follows recent news that destabilisation of part of the West Antarctic ice sheet has already begun and could be 'unstoppable.' Professor LeDrew added that scientists can use the data to show see where the edge of a glacier is, or where the ice is thinning as land bound glaciers expand towards the sea. Ships also use the information for navigation, he says. The map is currently available free of charge to the public online, via the Polar Data Catalogue. 'The Earth's polar regions are considered a bellwether for the effects of climate change,' said Professor LeDrew. 'When compared to the previous Antarctic mosaic, we can map changes in the icescape with unprecedented accuracy and confidence.' A similar mosaic for Greenland is currently underway and the researchers plan to continue creating mosaics of Antarctica every few years in order to track ice cover. Earlier this year, Nasa said vast glaciers in West Antarctica seem to be locked in an irreversible thaw linked to global warming that may push up sea levels for centuries. In a few hundred years they say the irreversible melt that has already started could eventually add four to 12ft (1.2 to 3.7m) to current sea levels. A Nasa study looking at 40 years of ground, airplane and satellite data of what researchers call 'the weak underbelly of West Antarctica' shows the melt is happening faster than scientists had predicted, crossing a critical threshold that has begun a domino-like process. Evidence shows 'a large sector of the West Antarctic ice sheet has gone into a state of irreversible retreat', says lead author Eric Rignot of the University of California, Irvine, and Nasa's Jet Propulsion Laboratory in Pasadena, California. The coastal ends of the glaciers rest on bedrock below sea level, holding back a vast weight of ice and making them vulnerable to melt, he said. 'It does seem to be happening quickly,' says University of Washington glaciologist Ian Joughin, lead author of a separate study into the same phenomenon. 'We really are witnessing the beginning stages.' Zoom in on this image to see the world's most complete map of Antarctica
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