THE NEWS LAST WEEK THAT SUMMER ICE COVERING THE ARCTIC OCEAN WAS TIED FOR THE SECOND-LOWEST EXTENT ON RECORD IS A SOBERING REMINDER THAT THE PLANET IS SWIFTLY HEADING TOWARD A LARGELY ICE-FREE ARCTIC IN THE WARMER MONTHS, POSSIBLY AS EARLY AS 2020. After that, we can expect the ice-free period in the Arctic basin to expand to three to four months a …