Last year 12,400,000 km² of Arctic ice caused a warm winter in the Eastern US. This year the identical amount of ice is causing a cold winter. Both years were +/-two standard deviations, meaning that they were normal.
Climate models can differentiate between normal amounts of ice one year and identical normal amounts of ice the next year, and hindcast whatever the weather was that just happened. The government has spent many tens of millions of dollars perfecting this technology.