Persistent cold temperatures in the Midwest this winter almost completely frozen over many of the Great Lakes. The Great Lakes Environmental Research Laboratory (GLERL) reported that 88 percent of the Great Lakes were frozen as of mid-February.

Among the questions triggered by the entrapment of a Russian ship near Antarctica on Christmas Eve were whether the ice conditions were out of the ordinary, and, if so, whether long-term climate change was playing a role.

The Arctic Oscillation describes simultaneous, geographically “choreographed” shifts in multiple features of the polar vortex: air pressure, temperature, and the location and strength of the jet stream. They all follow the hemisphere-wide oscillation of atmospheric mass back and forth between the Arctic and the middle latitudes, sort of like water sloshing in a bowl.

Meteorologists have known for years that the pattern of the polar vortex determines how much cold air escapes from the Arctic and makes its way to the U.S. during the winter. Climate scientists are wondering if a warmer Arctic could explain its odd behavior in recent years.

The most likely explanation for the lack of significant warming at the Earth’s surface in the past decade or so is that natural climate cycles caused shifts in ocean circulation patterns that moved some excess heat into the deep ocean.