We have seen winters over the last few decades become increasingly severe. Some times, the winter is harsh, while other times it is very mild. There have been a lack of 'average' winters. Now, new research indicates this may be due to the melting of Arctic sea ice.
As ice melts in the summer the ocean absorbs sunlight and stores it as heat. Previously, much of the sunlight was reflected back into space by the bright ice that covered the Arctic Ocean year round. But now, thanks to global warming, much of the Arctic Ocean that use to be ice covered is now ice free and more energy is being stored in the region as a result. As the summer turn to fall the amount of sunlight falling on the Arctic Ocean decreases and the amount of energy being stored begins to drop. As a result of this, the energy that was stored in the summer time is released into the atmosphere. This changes the difference in air pressure between the arctic and the lower latitudes, resulting in changes in the jet stream.
The jet stream curves northwards and southwards as it moves from west to east. This means some areas will see the jet stream far to the north, which will allow warm southern air to move northwards. Other areas will see the jet stream move to the south, allowing cold arctic air to move down. This means areas of the world will have severe winters while other areas will have mild winters at the same time. That is just what we saw this past winter. The U.S. was very mild while Europe was very severe.
Even if the details of this research are not correct the basic principle still is. The Arctic Ocean is storing great amounts of extra heat in the summer time above what it use to store. That energy is then being released into the atmosphere and will result in changes to weather patterns. The atmosphere is a heat engine. If you juice it up with more energy you are going to get results. It is like stomping on the gas pedal in your car.
What will the winter be like this year? We don't know. We can't make forecasts that far in advance. But, you should be prepared for something severe, one way or the other.