Main findings:

The observed 2012 record low in Arctic sea ice extent is extremely unlikely to have occurred due to internal climate variability alone, according to the models, i.e., and has a much greater likelihood of occurrence in the “forced plus internal variability” scenario. The 2012 anomaly is significantly stronger than the multimodel’s mean response to both anthropogenic and natural forcing combined.

Full report:

EEE 2012: Explaining Extreme Events of 2012 from a Climate Perspective