When Will the Summer Arctic Be Nearly Sea Ice-Free?

Despite the recovery of summer sea ice extent in 2013 relative to the record minimum in 2012 (5.1 versus 3.4 M km2), sea ice loss remains a major indicator of global change.  2013 is still the 6^th lowest sea ice extent and it well known that that one should consider the contributions of natural variability in weather patterns and ocean conditions in addition to long term downward trends. Better indices of change are sea ice thickness, the amount of old multiyear sea ice, and thus sea ice volume that has decreased by 75% since 1980.  Recovery of multi-year, thick, old sea ice would be particularly difficult, thus preventing Arctic climate from returning to the state of a decade or more ago. Further, observations and physical understanding support the conclusion that most global climate model results in the recent IPCC 5^th Assessment Report archive are too conservative in their sea ice projections of summer sea ice loss of 2050 and beyond. Time horizons for a nearly sea ice-free summer from data extrapolation and physical understanding suggest a summer sea ice loss roughly 2020 to 2030. Major sea ice loss is already occurring north of Alaska. In contrast to model results, data suggest an immediacy to climate change adaptation for the Arctic over the next few decades. Mitigation efforts are necessary to reduce the impact of temperature increases in the second half of the century. Recent data and expert opinion should be considered in addition to model results to advance the very likely timing for future sea ice loss to the first half of the 21st century, with a possibility of major loss within a decade or two.