Chaotic winter in the Northeast — could this be a signature of climate change?

In recent years natural disasters have become increasingly frequent in the U.S. Over the last year alone, Houston contended with one of the heaviest rain storms in U.S. history, the Florida Keys, Puerto Rico and neighboring islands were harshly affected by two back-to-back Category 5 hurricanes. Major parts of Pacific coastal states were incinerated by record wildfires. With the onset of winter came anticipated relief. However, climate-related disasters did not relent. They only relocated.

This week, the eastern states brace for yet another nor’easter while still half buried by two back-to-back storms that delivered up to two feet of snow to parts of Massachusetts.

{mosads}In one case, a “bomb cyclone” packed enough energy to topple power lines, leading to blackouts from Virginia to Maine. Only months prior, the region experienced record cold. In Boston, the maximum daily temperature in December reached a new low of 12 degrees, breaking the city’s prior record of 18 degrees set in 1924.

According to the U.S. Global Change Research Program, the Northeast has been experiencing increased extreme precipitation, with a more than 70 percent rise in the amount of precipitation falling in “very heavy” weather events over the 1958 to 2010 period.

Of the 10 heaviest snowstorms in Boston, five occurred since 2000 — with two taking place in the same two weeks of 2015, making it the all-time snowiest season for the city. Living in nearby Cambridge at the time, I can recall cross-country skiers taking to Massachusetts Avenue in the wake of the storms. Not your everyday sight.

Extreme weather has not been all cold news for the Northeast. While February typically means painfully cold weather — often reaching single digits — this year saw T-shirts and shorts as temperatures in some areas soared above 70 degrees for the second year in a row.

In 2017, 19 areas across the Northeast experienced their warmest February on record, including Washington D.C., Philadelphia, Buffalo, and Baltimore. Daily temperatures that month broke records dating back to 1906. Also of note that month was the first tornado to ever touch down in February in Massachusetts since official records began in 1950.

While New England is known for its unpredictable weather, recent temperature extremes have been uncharacteristic. Scientists attribute this unusual weather to the instability of the so-called polar vortex.

As the name suggests, polar vortices are circulating wind patterns that sit over earth’s poles. When they are strong, frigid temperatures remain relatively isolated to the polar regions. However, recent warming trends have weakened these winds. In the north, this has caused the vortex to meander more on its otherwise circular path around the pole.

This meandering motion has allowed frigid Arctic air to dip further south over certain regions, while warmer equatorial air penetrates further north. This heat exchange explains why December brought record cold to the Northeast while Alaska basked in record warmth — temperatures in Fairbanks averaged 20 degrees above normal according to The Washington Post.

Two weeks ago, temperatures in the North Pole similarly soared above freezing despite the region still being enshrouded in total winter darkness — setting a new February heat record according to the Danish Meteorological Institute. February temperatures for the region normally average about -27 degrees.

In a recent interview, Jason Box, who is a professor in glaciology at the Geological Survey of Denmark and Greenland, ascribed recent temperatures abnormalities across the northern U.S. and Arctic to greenhouse warming “enhanced by human burning of fossil fuels.” He described the Arctic as “warming at twice the rate of areas to the south” and called the instability of the polar vortex a “signature of climate change.”

As weather events across the U.S. break records in all directions, the phrase “climate weirding” comes to mind. However, beyond the chaotic weather extremes emerges a pattern. A comparison of daily record high temperatures with record low temperatures averaged across the U.S. reveals a trend toward increasing record highs over time.

According to a study by the National Center for Atmospheric Research, the current ratio of record high to record low temperatures is about 2:1; with model simulations suggesting this ratio could increase to 20:1 by mid-century. This indicates a warming trend consistent with the message echoed by climate scientists worldwide.

Given increases in extreme weather and climate-related disaster, public pressure for climate action continues to mount. In the last year, the House Climate Solutions Caucus, composed equally of Democrat and Republican members of Congress, has grown from 26 to 72 members. This mobilization is meaningful.

Though the U.S. announced its position last year to withdraw from the Paris Climate Accord, Professor Box offers words of optimism, “I remember when that news came in over a year ago. I think it actually gave more resolve to people who have a job to do, and that is to make a transition to a more sustainable economy.” How such resolve will play out remains to be seen.

Shahir Masri, Sc.D., is an assistant specialist in air pollution exposure assessment and epidemiology at the University of California at Irvine, and also teaches at the Schmid College of Science and Technology at Chapman University. He earned his Doctor of Science and Master of Science degrees from the Department of Environmental Health at the Harvard T.H. Chan School of Public Health.