Global warming could weaken the ice-soil mixture called permafrost in areas surrounding the Arctic Circle, causing damage to buildings, pipelines and electricity generating stations, according to a study done at University of Delaware, USA. Large cities in Siberia and smaller ones in Alaska and Canada run the risk of being affected. "What we're trying to accomplish in the paper is to show areas in which this hazard potential is there,' said Fredrick Nelson, author of the research paper. He used a 1997 map showing areas of permafrost and calculated the degree of thawing that would be caused by a rise in temperatures predicted by global warming and "superimposed a map of existing human infrastructure to study the possible damage ( Nature , Vol 410, No 6831).