The Northern Hemisphere has been witness to a series of unusual weather patterns over this past winter. In Canada, a polar vortex blowing south over Canada has contributed to the Great Lakes freezing over almost completely, a phenomenon that hasn’t happened for decades. The increasingly number of irregular weather events this winter has spurred debate amongst climate scientists as to how these events are connected to climate change and warming in the Arctic. A report put out by the United Kingdom Meteorology Office in February theorizes that persistent patterns of perturbations in the polar jet stream over the past winter have lead to these hemispheric patterns of irregular weather.
Though it is difficult statistically to link a long-term trend to day-to-day weather, more and more evidence suggests that these irregular and record-breaking weather events are consequences of climate change heating up the Arctic.
Research has been looking at how Arctic warming is changing the polar jet stream, which is a high altitude wind that encircles the globe. This jet stream is the key factor influencing the weather experienced in the Northern Hemisphere.
This polar jet stream is well understood by climate scientists. Because warm air is less dense than cold air, it rises above it. So when warm air parcels from the south travel northward, they sit atop the cold Arctic air. The greater the difference in temperature between these two air parcels, the faster the jet stream moves across the Northern Hemisphere. But when the temperatures of these air parcels are disrupted, the weather events that travel with the stream are disrupted as well. Loss of Arctic sea ice is linked to increased heat in the atmosphere, as sea ice cover acts as a lid that separates the ocean from a colder atmosphere. As increasing amounts of sea ice are lost, the Arctic is becoming incrementally warmer, and the temperature difference between these two air parcels is lessening, causing a slower, weaker jet stream. The change in speed of the jet stream’s movement is causing for a more convoluted path, and weather patterns are disrupted and tend to remain in one place for longer periods of time. In theory then, when weather is especially hot, wet, dry, or cold, it will tend to stay in this state for longer, thus increasing the chance of flooding, drought, and other extreme weather events.