Winter is the coldest season of the year and these past few days have been proof of that. And while the snow days and chill we experience this season are far from abnormal, however, the extremities sure aren’t! You may be wondering why this winter is extra cold, especially since climate change has become increasingly worse. It is for two reasons: our atmosphere and the polar vortex.

The polar vortex is a large area of cold air and low pressure that surround our planet’s poles and always exist there. Its intensity, however, is determined by the season we are currently experiencing. In summer the polar vortex weakens, whereas in winter it strengthens. When the vortex is at its strongest, it is typically stable—the cold air it holds being well contained. On the contrary, when it’s at its weakest, the cold air is unstable and can be displaced from the high pressure zones from our planet’s middle latitudes, causing the vortex to move from its original location in the north farther south. When this occurs, the dry, frigid air from the vortex comes into contact with warm, moist air, causing a cold snap.

This occurrence is worsened by the fact that climate change has caused a phenomenon known as sudden stratospheric warming, essentially meaning the upper layers of our atmosphere rise in temperature in a matter of a couple days, causing warmer land temperatures. These warmer land temperatures allow more heat to be transported into the Arctic stratosphere. As our planet warms, it makes these stratospheric warming events happen more often, which then destabilize the polar vortex, causing extreme weather, such as what we’ve been experiencing over the past couple of days in the U.S.

While the reason behind our recent weather is complex, it makes all more simpler our reason to work towards stopping climate change (even if we want extra snow days).