The long-term trend is for climate change to alter weather patterns.
With the enormous snowstorm the east coast of the United States received over the weekend — some areas got upwards of 40 inches of snow — you may be wondering if such extreme storms are a sign of a changing climate.
Unfortunately, it is not an easy question to answer. Although scientists are able to show that some specific weather events, such as extreme temperatures, are linked to greenhouse gas emissions, it is more difficult to link other weather phenomena to climate change — including the recent snowstorm.
However, climate scientists say the overall long-term trend is for climate change to alter weather patterns, causing more severe snowstorms, even as winters become milder. According to a 2014 federal report on climate change impacts in the United States, there is evidence of an increase in frequency and intensity of winter storms since 1950, even though the amount of snowfall has decreased over the country. This means that although we are getting less snow overall, we are getting more of it at once during extreme weather events.
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But this seems counter intuitive right? If the climate is warming, why would we get more snow during storms? According to the National Oceanic and Atmospheric Administration (NOAA), rising surface temperatures are causing increased evaporation, leading to more water and heat in the atmosphere.
Added heat in the atmosphere weakens the polar vortex — high-latitude winds in the North that confine cold Arctic air — and warming allows this cold air to move southward, creating some really cold weather conditions.
The extra moisture and increased precipitation is usually more pronounced for coastal winter storms, such as nor’easters. A nor’easter is a storm that contains very strong northeasterly winds, typically seen along the east coast of the United States and Atlantic Canada, between the months of September and April.
These storms can become so powerful that they contain hurricane-strength winds. However, instead of forming the well-known swirling vortex hurricane shape, nor’easters look more like a comma (as seen in the above image).
A warming climate also causes shifts in the North Atlantic Oscillation (NAO) — the difference between atmospheric pressure in Iceland compared to the Azores. A shift in the NOA affects the direction and strength of the jet stream, altering temperature and pressure patterns across the eastern parts of North America.
A weakening of the polar vortex and this shift in the NOA are happening right now — driving much of the extreme weather we have been witnessing recently.