A study of glaciers suggests the ice sheet in east Antarctica could be more vulnerable to climate change than previously thought, British researchers say. Geographers from Durham University said they used declassified spy satellite imagery to create the first long-term record of changes in the edge of outlet glaciers where they meet the sea along 3,400 miles of the East Antarctic Ice Sheet coastline. The imagery, covering almost half a century from 1963 to 2012, showed the glaciers underwent rapid and synchronized periods of advance and retreat that coincided with cooling and warming, a Durham release reported . \"We know that these large glaciers undergo cycles of advance and retreat that are triggered by large icebergs breaking off at the terminus, but this can happen independently from climate change,\" Durham researcher Chris Stokes said. \"It was a big surprise therefore to see rapid and synchronous changes in advance and retreat, but it made perfect sense when we looked at the climate and sea-ice data.\" Causes of recent trends in air temperature and sea ice were difficult to determine but were likely to reflect a combination of both natural variability and human impacts, Stokes said. \"If the climate is going to warm in the future, our study shows that large parts of the margins of the East Antarctic Ice Sheet are vulnerable to the kinds of changes that are worrying us in Greenland and West Antarctica -- acceleration, thinning and retreat,\" he said. The East Antarctic Ice Sheet holds the vast majority of the world\'s ice -- enough, if melted, to raise global sea levels by more than 150 feet, the researchers said.