The role of the ocean and atmosphere in creating an ice free Arctic

A decrease in the Arctic sea ice cover of 2.9% per decade has been observed in the last decades, particularly in summer. Currently, there is speculation in the scientific community that the Arctic may actually become seasonally ice free as global warming continues. Mechanisms that could be responsible for an ice-free Arctic Ocean are presented. In particular the relative importance of (1) increased downwelling longwave radiation, (2) changes in the atmospheric circulation , and (3) increased vertical ocean heat transport (all potentially associated with an increase in the greenhouse gas concentration) in shaping an ice-free Arctic are discussed. To this end, results are presented from a stand-alone sea-ice model where atmospheric and ocean forcing fields are varied independently. In these simulations the range of forcing is specified from 21st century climate change integrations of the IPCC 5th assessment.