Reuters: Global warming will leave the Arctic Ocean ice-free during the summer within 20 years, raising sea levels and harming wildlife such as seals and polar bears, a leading British polar scientist said on Thursday. Peter Wadhams, professor of ocean physics at the University of Cambridge, said much of the melting will take place within a decade, although the winter ice will stay for hundreds of years. The changes will mean the top of the Earth will appear blue rather than white when …