Arctic sea ice appears to have stopped melting for the summer, leaving behind the second-greatest expanse of ocean than any year since scientists began measuring, according to a report released this week by the National Snow and Ice Data Center at the University of Colorado. There was slightly more ice-melt last summer, the NSIDC said, but the preliminary 2008 data show nearly 1 million square miles less sea ice than average over the last 30 years.