Decline of Arctic sea ice: Evaluation and weighting of CMIP5 projections

Trends of Arctic September sea ice area (SSIA) are investigated through analysis of Coupled Model Intercomparison Project phase 5 (CMIP5) data. The large range across models is reduced by weighting them according to how they match nine observed parameters. Calibration of this refined SSIA projection to observations of different 5 year averages suggests that nearly ice‐free conditions, where ice area is less than 1 × 106 km2, will likely occur between 2039 and 2045, not accounting for internal variability. When adding internal variability, we demonstrate that ice‐free conditions could occur as early as 2032. The 2013 rebound in ice extent has little effect on these projections. We also identify that our refined projection displays a change in the variability of SSIA, indicating a possible change in regime.