We have enjoyed a remarkably mild fall on the coast this fall. That’s probably not surprising, given that we just had a remarkably warm and dry summer. Personally, I have no issue with keeping the house’s heat off for a while longer, or picking cold-hardy lettuce from my garden in November. I do, however, worry that the short-term benefits I enjoy mean a long-term problem for the world. That is because the warmth we are experiencing is also taking place in the Arctic. 

As has been reported widely, the Arctic has been too warm this fall. Back in mid-October, when the sun sank below the Arctic horizon for the winter, sea ice on the Arctic Ocean stopped forming. By the end of the month, a section of ice about the size of the eastern United States had failed to form. The absence of this ice is made more astonishing because when the Arctic turns dark, temperatures typically get a bit chilly, ranging from -40°F to just below freezing during a normal year. This has not been a normal year. In early November, some parts of the Arctic were experiencing air temperatures 36°F above normal.

Scientists think that the reason for the warmth is connected to the jet stream. In mid-October, the jet stream set up several troughs that dipped deep into northeast Asia and the North Atlantic. The troughs reached into latitudes with warm and moist air and drew large volumes of that air into the Arctic. And those troughs haven’t budged.

Changes to the jet stream are related to a warmer climate. The jet stream is powered in part by the sharp temperature differences between the Arctic region and the temperate areas of the globe. That difference has grown markedly less in the past decade. According to Rutgers University climate scientist Jennifer Francis, the jet stream in North America is 14 percent slower in the fall than it was in the 1990s. Instead of moving straight to the east, this slower jet stream undulates to the north and south. The slower it goes, the deeper the troughs, meaning even warmer air can be imported to the Arctic. Francis’ research also showed that the jet stream is creating more stationary high pressure systems that keep weather patterns in place for extended periods.

In addition, Arctic Ocean sea ice was at a record minimum this summer. That means that there’s more open water, which is dark-colored, to absorb sunlight. Sea ice, by contrast, is white and thus reflects incoming sunlight rather than absorbing it. Researchers predict that the Arctic Ocean could have entirely ice-free summers by the 2030s.

While Arctic fall temperatures of 36°F above normal might just be a fluke, the long-term implications of such warmth are sobering. The recently released Arctic Resilience Report produced by the Arctic Council (members of which include the eight countries that border the Arctic) noted that changes to the Arctic have “global implications.”

One of those implications was pointed out by scientist Wallace Broecker in the mid-1980s. Broecker, a Columbia University scientist at the Lamont-Doherty Earth Observatory, coined the term “global warming” in a 1975 paper on carbon dioxide levels and atmospheric temperature. He went on to prove that the world’s oceans play a significant role in the global climate. In his research, he found that major ocean currents are linked together in a great “ocean conveyor belt,” powered by differences in temperature and salinity, which shifts and balances heat across the planet.

Broecker also found that this conveyor belt had broken down in past eons. A sudden influx of freshwater in the North Atlantic Ocean had put a wrench in the system by decreasing the salinity of the cold water. The alteration of the conveyor belt caused sudden climate cooling and warming events, many of which were recorded in the ice cores of Greenland and the Arctic. These abrupt climate changes, as he termed them, took place in the course of centuries and even decades.

Despite its warmth, the Arctic Ocean isn’t contributing much to this influx of freshwater; Greenland is. The ice-covered island had its warmest winter on record last year and began its annual period of melting earlier this year than ever recorded, in April. On July 19, more than 11 billion tons of ice and snow was lost to the ocean in a single day. Torrential rainstorms flooded the northwestern region of Greenland during the summer months, further eroding ice. Warmer weather and more unclouded days due to a persistent high pressure system over Greenland also contributed to ice melt, continuing a trend that researchers have noted for several years. Thirty-six million square kilometers (13.9 million square miles) of surface ice melted during the three-month summer.

I feel slightly guilty about the fact that I can sit on my front porch at noon on a clear November day and eat my sandwich in comfort. I haven’t even scraped much ice off my car windshield in the morning. The roses haven’t yet been covered in fir boughs for winter protection because the ground around them isn’t frozen. It’s discomforting to think that these mild and temporary pleasures may be linked to irreversible global changes in the not-so-distant future.

For more information about Greenland and ice melt this year, go to the National Snow and Ice Data Center report, http://nsidc.org/greenland-today/2016/10/2016-melt-season-in-review.