evidence: The Arctic could see summer days with practically no sea ice as early as the next couple of years, according to a new study out of CU Boulder. [...] The good news: Arctic sea ice is resilient and can return quickly if the atmosphere cools down. "Unlike the ice sheet in Greenland that took thousands of years to build, even if we melt all the Arctic sea ice, if we can then figure out how to take CO2 back out of the atmosphere in the future to reverse warming, sea ice will come back within a decade," Jahn said.