The prolonged bitter cold snap over the holidays has affected 139 million Americans. Still, this weather effect was localized — the U.S. comprises less than 2 percent of Earth’s surface area. Many other parts of the planet were much warmer than normal.
Then, on Jan. 4, Winter Storm Grayson brought whiteout conditions to the U.S.’s East Coast from Maine to Virginia. It was the strongest, most intense Western Atlantic winter storm in four decades, causing major coastal flooding and one of the heaviest snow and ice events to much of the Southeast. Like a “winter hurricane,” it brought moisture from the south, which collided with the super-cold arctic air. The result: lots of snow instead of torrential rain. Grayson’s hurricane-force winds created blizzard conditions and power outages. Then the storm crossed the North Atlantic and caused major wind damage in England, Ireland, and France.
What’s going on?
A study published last spring in the journal “WIREs Climate Change” lays out how a warming Arctic and melting ice appear to be linked to cold weather farther south. According to the study, persistent winter cold spells (as well as the western drought, heat waves, and heavy storms) are related to rapid Arctic warming, which, in turn, is caused mainly by human-caused climate change.
Climate scientists expect record-breaking cold spells to occur less often in the future, but they will likely last longer. Normally, cold air swirls around the polar vortex, a low pressure area around the North Pole bounded by the jet stream. The vortex itself is not caused by global warming or climate change. However, researchers have found that loss of Arctic ice and heavier snow cover in northern Asia weaken the jet stream, which draws its energy from the temperature difference between Arctic and equatorial climes.
Up until 2000, the jet stream looked like a skull cap on the planet, containing the Arctic cold. Since then, it has come to resemble a wavy snake, allowing cold air to migrate south and warm air north. Such weather patterns come about due to a combination of abnormally warm ocean temperatures in the eastern Pacific Ocean and loss of sea ice in the warming Arctic. Clearly, Arctic warming is related to climate change.
In addition, the warm ocean temperatures off the U.S. West Coast cause the jet stream over North America to “bulge” northward. This has caused unusually warm temperatures from California to Alaska — during the first days of January it was colder in Jacksonville, Fla. than in Juneau. At the same time, the jet stream is being pushed farther south as it travels west to east.
In brief, when the jet stream is strong, the polar vortex is stable and encloses polar air around the pole. In contrast, a weak jet stream allows the polar vortex to bulge, permitting cold air to spill south in one area and warm air to move north in the next. A stable polar ice cap seems to correspond to a strong, stable jet stream. With Arctic warming, the polar ice melts, reducing the energy that drives the jet stream, thus weakening it. It begins to slow, meander, and even stall, locking in weather that would normally move on. If this hypothesis is correct, we are looking at permanent change in the climate: more powerful weather events, including prolonged hot spells in summer and cold spells in winter.
The Earth’s global temperature has been steadily increasing. It was the hottest on record in 2016, according to NASA and NOAA. In a 2017 report, NOAA declared that Arctic temperatures are rising at twice the rate of the global temperature rise. This means that, as a feedback effect, the more sea ice melts, the less sunlight is reflected off the sea surface and the more heat is absorbed by the water.
The decrease in Arctic ice has been especially dramatic since 2000. Still, it will take more time to definitively conclude that climate change causes colder Arctic air to move farther south more frequently. On the whole, though, our greenhouse gas emissions are certainly warming the planet and storms are becoming more damaging.
(Paul Kando is a co-founder of the Midcoast Green Collaborative, which works to promote environmental protection and economic development via energy conservation. For more information, go to midcoastgreencollaborative.org.)