Winter just isn’t the same these days in the North Pole region. At a time of the year when we expect to see maximum Arctic sea ice area for the winter season, the 2018 winter maximum area ranked among the lowest years (#1: 2017, #2: 2018, #3: 2015, #4 2016). Nick Mailloux calculated that the historical average for maximum Arctic sea ice area is slightly larger than twice the size of the contiguous United States, but in 2017 the area lost was more than the size of California, Nevada, Utah, and Arizona combined. The northernmost city in the U.S. – Utqiaġvik (formerly called Barrow), Alaska – had record warm temperatures this winter. Perhaps the biggest shocker though, was the North Pole went above freezing this winter (20 to 30 degrees Celsius or 36 to 54 degrees Fahrenheit above average). Records are being broken across the Arctic winter of 2017/2018 consistent with a larger trend.
Figure 1: The Arctic zone is warming more than twice the global average temperature. Source: NASA GISS
A warmer arctic is part of a trend since 1990 that scientists refer to as “Arctic Amplification.” This refers to the amplified regional response to global warming. The red colors in the NASA GISS plot for zonal average temperature change over time, indicate that the Arctic zone has warmed more than twice the rate of the global average temperature rise (see Figure 1). Two new studies add to the mounting evidence regarding correlations with Arctic Amplification and changing severity of weather patterns in North America and Eurasia. Time to check in on the implications of these studies as we’re witnessing the extraordinary string of Nor’easters pounding New England this winter season.
Warmer Arctic correlated with more frequent cold outbreaks elsewhere in winter
The Arctic used to be so cold during the winter it was as if a fence surrounded it, keeping the coldest air trapped within the North pole region. A weak spot in the fence could, on rare occasions in the past, lead to cold outbreaks southward into the continental U.S. or Eurasia–these spots are becoming more frequent. The fence can break the other way, causing the warmer air from the south to also penetrate further north. Hence the many records mentioned above are being broken across the Arctic this winter while parts of the continental U.S. and Eurasia log colder than expected temperatures. This “fence” in the high atmosphere is called the stratospheric polar vortex. Unlike a fence that takes time to be repaired and designates a fixed boundary, the stratospheric polar vortex is dynamic. Therefore, the boundary position changes over time and interacts with other dynamic parts of the atmosphere and ocean.
Science suggests the behavior of the polar vortex is changing with a warming climate, which is starting to tip the scales, but in both directions. During any given winter, parts of mid-latitude North America and Eurasia experience periods of cold and warm weather, but in recent years the differences between them are typically greater – the colds are colder and the warm periods are warmer.
Building upon many studies over recent years, Kretschmer and colleagues correlated when the stratospheric polar vortex was weak (when the fence breaks), northern Eurasia and Canada were colder than normal. A strong stratospheric polar vortex (when the fence holds) was associated with warmer temperatures in northern Eurasia and the eastern United States and colder temperatures over Alaska and Greenland. Their study published in January advances our understanding of a winter (January through February) pattern observed from 1990 through 2015. Furthermore, the researchers suggest that seasonal forecasts could be greatly improved by paying attention to the conditions that are observed before a weakened polar vortex event occurs in the winter.
What does this mean for the 2018 Nor’easter season?
Figure 2: Strong 2017/2018 winter and spring Nor’easter season for New England (i.e. colder than normal eastern U.S. surface temperatures and warmer than normal ocean waters off the U.S. east coast).
A recent study by Cohen, Pfeiffer and Francis found that the time of Arctic Amplification (1990-2015) correlates with increased occurrence of heavy snowfall in the northeastern US, but decreased occurrence in the western US, compared with the time period before (1950-1989). Research is ongoing to better understand the physical mechanisms for these observations. For now, we can examine the wacky weather that helped create ideal conditions for the ‘Nor’easter’ storms happening in rapid succession over New England this season.
Northeastern storms typically occur when there is a seasonal difference between the relatively warmer ocean compared to the adjacent colder land. First condition was met – a warmer than normal ocean temperatures off the U.S. east coast for this winter season (see Figure 2). The second condition was also met – the eastern U.S. in January 2018 was colder than normal for this time of year. Not surprising since there was record-breaking sea ice loss this winter coupled with other strong signals of Arctic warming as well as a polar vortex so weak it split in two.
What does this mean for Alaska and other high northern latitude regions?
Recall that when the stratospheric polar vortex is weak, not only can cold outbreaks penetrate further south, but warm air from the south can also penetrate further north than would be typical in the past. These warm air incursions into the high north is part of why record warmth occurred this winter season in northern Alaska, northern Greenland, and the North Pole (remarkably above freezing). Alaska had its fourth warmest December through February on record (Figure 3). My colleague, Tosin Fadeyi, pointed to some grave consequences for Alaskans grappling with warmer than expected conditions. Alaskans who depend heavily on subsistence-based hunting face severe challenges from lack of ice and mild winter weather. There have been so many holes in the ice highway along the Kuskokwim River this winter, the community ran out of reflective tape to alert of the dangers. At the end of January a family fell into a hole in the Kuskokwim river ice highway; five survived and tragically one perished. This warm winter season was preceded by unseasonably warm autumn. The northernmost town of Utqiagvik (formerly Barrow) historically depended on sea ice to protect it from the autumn storms. Sea ice can dampen the ability of a storm to generate waves. Little or no ice can expose the coastal community. Utqiagvik sustained around $10 million in damage from a storm at the end of September.
Figure 3: Alaska is warming up. Alaska Climate Research Center UAF
Families in New England and Alaska Bearing the Costs of this Winter Season
Perhaps the residents confronting a string of Nor’easters have more in common with Alaska residents than at first glance. Some have compared these Arctic cold outbreaks to a freezer door being left open for a period – frigid air escapes and chills the kitchen and simultaneously the warm air from the room fills the freezer. More than two million in 13 states in the northeast have suffered power loss after just one nor’easter this season; in Massachusetts, three times in two weeks a storm has resulted in hundreds of thousands of homes and businesses being left without power.
Families suffering multiple days without power may have to throw out an entire freezer and refrigerator-load of food and may seek warm shelter. Alaska residents who don’t want to risk travelling on ice highways with dangerous holes may not reach traditional hunting grounds to feed their families and their communities. Families in both Alaska and Eastern U.S. regions are now bearing the costs of the disruptions to activities that used to be sufficiently adapted to the seasons of the past. Now ice highways can have dangerous holes and the infrastructure supplying power to homes may not be up to the task of withstanding a string of intense storms.
More and more communities are taking note, discussion tradeoffs, and finding creative solutions for more resilient communities. For the sake of our families, friends and neighbors.
[UPDATE 3/30/2018 9:37am: We updated the post to reflect that this year’s maximum sea ice extent is among the lowest measured].