Attribution of Sea Ice Changes Across all Seasons Invited Paper 401612

Over the last several decades, the Arctic Ocean sea ice cover has shrunk by 40-50% during summer. The lowest extent on record occurred in September 2012 when the extent dropped to 3.41 10⁶ km². While ice loss in winter has been less extensive than during summer, the last two years have seen persistently low ice conditions during all months of the year. In fact the largest departures from average conditions occurred in May and November of 2016, exceeding that seen in September 2012.

The rapid loss of Arctic sea ice across all seasons is primarily driven by a combination of anthropogenic greenhouse gas emissions and internal variability. However, the relative proportion of these two drivers remains highly uncertain. One reason for this uncertainty stems from the wide spread in modeled internal variability and in the wide spread in the modeled forced signal.

Here, we estimate the proportion of these two drivers primarily from the observational record using robust relationships between Arctic sea-ice coverage and both global mean temperature and anthropogenic emissions of CO2. This allows us to not only examine the specific drivers of the sea-ice loss during summer, but instead for every month of the year.