The extent of Arctic sea ice dropped to 3.41 million square kilometers on 16 September, 760,000 square kilometers below the minimum ice extent in 2007, which had been the low mark since the satellite record began in 1979, the National Snow and Ice Data Center (NSIDC) announced. Overall ice extent is 50% below where it was in the 1970s, NSIDC research scientist Walt Meier said during a 19 September briefing. He added that there is also a decrease in ice thickness. Meier said that sea ice varies from year to year with lots of ups and downs. “We wouldn't expect it to keep going down, straight off the map so to speak,” he said. “Typically after a record low, we've seen it rebound.” Meier added that the general long-term trend is for the Arctic to continue to become generally ice free. He said it is difficult to know how long it will take for that condition to be reached; because of strong variations, Arctic sea ice extent could plateau for some time.