It is undisputed that the entire Earth is connected, and this holds true for natural processes as well. Although the wing flap of a butterfly will not cause a hurricane on the other side of the world, the Earth’s climate is interlinked and what happens in one region may have an impact on the climate of another.

Severe Winter Storms

The United States has recently suffered an onslaught of the most severe winter storms of the century. In 2019, the “polar vortex” swept across the midwestern U.S., causing temperatures as low as 60 degrees below zero with the windchill factor. In 2018, Winter Storm Zanto spanned from the Gulf Coast to the Great Lakes. It caused heavy snow, hail the size of eggs, rain and wind gusts, as well as a tornado in Arkansas. In 2017, the Pi Day Blizzard resulted in more than 3 feet of snow in parts of Pennsylvania and New Jersey and blizzard-like conditions due to extreme winds. In 2016, Winter Storm Jonas broke records and became the fourth most powerful snowstorm in the north-eastern U.S. It affected more than 100 million people, and 14 different states experienced at least a foot of snow.

The list of extreme U.S. winter snow storms goes on and on, and a new study may have found one peculiar reason for these freak winter storms – warming in the Arctic.

Arctic Climate Change

The Arctic is warming at a rate of almost twice the global average. The average temperature of the Arctic has increased by 2.3 oC. Summer sea ice, critical to Arctic marine life, is melting at a rapid pace. This is threatening ice-dependent species, like polar bears, walruses and narwhals. The Arctic plays an important role in regulating the world’s temperature, and as more ice melts, the warmer Earth is becoming. Researchers have long suspected that warming in the Arctic could trigger weather anomalies in the winds around the North Pole, with consequences to the south.

Climate change is often called “global warming”, and people assume it will mean more heatwaves and less snowfall. However this is not true and climate change can result in more severe winter weather as well.

The Polar Vortex

One dominant feature of the atmosphere above the Arctic is the polar vortex. The polar vortex is a fast-flowing band of high altitude winds. It is always present above the Arctic (as well as the Antarctic), however it weakens in summer and strengthens in winter. The polar vortex is normally confined to the poles due to the warm air closer to the Equator. During winter in the Northern Hemisphere, the polar vortex may expand, sending cold air southward with a jet stream, which results in freezing temperatures in the U.S.

Connection Between Arctic Weather and U.S. Winter Storms

A new study published in the journal Science investigates variability and changes in Arctic weather with extreme winter weather events in the U.S. The researchers compared 40 years of satellite observations of Arctic atmospheric conditions with experiments based on computational climate models. The models aimed to determine how a decline in sea ice and snow in the Arctic would affect airstreams in the region. Ice and snow reflects the heat of the sun, and the dark ocean and landmass absorbs heat, therefore a decline in ice and snow increases warming of the Arctic.

The researchers discovered that periods where the polar vortex stretched have increased in the past few decades due to periods of heating in the Arctic. The computer models were able to reproduce this behavior well when they simulated the effects of Arctic warming. Heating in the Arctic disturbed the circular pattern of winds in the polar vortex, which allowed colder winds and weather to flow south to the U.S.

Dr. Judah Cohen, lead author of the paper and a professor at the Massachusetts Institute of Technology and director of Atmospheric and Environmental Research stated, “We know when temperature differences increase, that leads to more disruptions of the polar vortex. And when [the polar vortex] is weakened, that leads to more extreme winter weather such as the Texas cold wave last February.” The findings of the study are based on observations and modeling, and the results show a strong link between climate change and warming in the Arctic, and the stretching of the polar vortex and impacts on the ground, such as extreme “freak” winter storms in the U.S.

The idea that warming of the Arctic could cause extreme winter storms and cold events in more southern regions is still a hotly debated topic among climate experts. It seems natural to assume that winters will become milder on a warming Earth. Commonly used climate models that are used to study links between different components of Earth’s climate system differ on the issue of how Arctic warming may influence winters in other regions. State-of-the-art models also do not accurately replicate observed trends of the polar vortex. It is therefore possible that the models are missing something, or if the polar vortex is simply undergoing natural climate variability.

Although the new study found that changes in sea ice and snow cover seems to influence the polar vortex above the Arctic, other factors like changes in sea surface temperature may also cause anomalies in the atmosphere above the Arctic which could result in cold temperatures elsewhere. To further complicate things, it is still uncertain how Earth’s climate responds as a whole to changes in sea ice and snow cover at the poles.

The study indicates that warming of the Arctic is having a significant impact on winter weather in not only the U.S. and Canada, but also Eastern Asia. Despite the results of the study, it remains uncertain whether past and recent examples of extreme winter storms in the U.S. are predictions of future weather trends. At least if connections can be made between Arctic warming, the behavior of the polar vortex, and winter storms, then forecast lead time for such events can be extended and people can be better prepared for the freezing weather.