Global Warming

How global warming causes Europe’s harsh winter weather

Climate deniers are using a spell of unusually cold weather in Europe to incorrectly argue that CO2 emissions are not warming the planet. Their rather simplistic claim — which has been repeatedly debunked by climate scientists — is that extremely cold weather shows that carbon dioxide emissions are not warming the Earth.

In fact, the effects of global warming may even have favored the extremely cold temperature. The sub-zero temperatures and heavy snowfalls are more than just a cold winter. They are made more likely by the collapse of the polar vortex — a huge ring of cold winds raging in the Earth’s stratosphere — at the North Pole.

The polar vortex is closely connected to the jet stream, a band of strong winds about 10 kilometers above the ground. At the polar front, this flows between warm air from the tropics and subtropics, and cold polar air. The pressure extremes that form in this transitional area at lower layers are sometimes referred to in weather reports as the Icelandic low or the Azores high.

The jet stream usually determines the winter weather in Europe: if it is strong and flows from west to east, it brings mild, windy and rainy weather from the Atlantic, and holds the cold air from the Arctic.

But if the jet stream is weak and wavy, the polar vortex also weakens, and sometimes breaks down completely. The cold snap across Europe is the result of a weak jet stream — more precisely a dip — that has caused a strong and long-lasting collapse of the polar vortex.

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