Why is it so cold this winter?

1. Polar vortex: In some years, the polar vortex (the low-pressure area between the North Pole and the South Pole) may be extremely strong, causing cold air to flow from the polar regions to low latitudes, thus lowering the temperature in these areas.

2. Air-sea interaction: The ocean has an important influence on climate change. For example, the drop of ocean surface temperature may lead to the landing of cold air through air-sea interaction, leading to the drop of temperature.

3. La Nina phenomenon: La Nina phenomenon is a climatic phenomenon, which is characterized by abnormally low SST in the equatorial Pacific Ocean. This may lead to low winter temperatures in East Asia, because cold air can enter China from the north.

4. Climate change: Climate change is a global problem, which may lead to an increase in extreme weather events. This includes the cold weather in winter. Climate change is mainly due to the impact of human activities on the atmosphere, such as the emission of a large number of greenhouse gases, leading to global temperature rise.

The above information is for reference only. If you want to know in detail why it is so cold this winter, it is recommended to consult a meteorologist or consult relevant meteorological reports.