In the Northern Hemisphere, climate change has resulted in dramatic warming in the Arctic Region. Mean temperatures at Barrow, Alaska, have increased by more than 11 degrees Farenheit since 1976. Arctic Ocean ice cover has been decreasing dramatically.
As a result of warming, the polar jet stream over North America is increasingly getting into large- amplitude wave pattens in which it is far to the north on one side of the wave and far to the south on the other side. These wave patterns are more frequently getting stuck in unusually warm or cold positions. When the jet stream gets stuck way to the south of our position, Wisconsin experiences cold polar vortex conditions. Often, we experience those conditions when Alaska is warmer than usual. When the jet stream gets stuck way to the north of us, we experience above-normal warmth.