In what seems to be an encore to last winter’s disturbing display, temperatures in the Arctic have once again risen above the freezing mark. According to The Woods Hole Oceanographic Institution, the average temperature for the Arctic winter is -40ºF (-40ºC), but instead is currently hovering around 32ºF (0ºC).

Warm, moist air from further south is being circulated up into the Arctic by a powerful storm currently east of Greenland. Combined with record low sea ice, this creates an unhindered conduit for the comparatively humid air to be sent northward, maintaining the Arctic’s freakish weather. As a consequence, the polar vortex has returned, with cold Arctic air being displaced southward by the incoming warm air, causing unseasonably low temperatures in Canada and the northern U.S.

This is the second straight December to have seen this phenomenon, and this month follows a record-hot November for the region, when temperatures 18º above normal were recorded. On December 30 of last year, the north pole was recorded to have been a full degree warmer than Seattle, WA, was at the time, and this year appears to be following suit. According to a study published in the journal Nature, warming periods like this appear to have happened once every five to ten years since 1959, but that their frequency and intensity appear to be increasing at an alarming rate — if this becomes an annual occurrence, the impact on Arctic sea ice levels could be devastating.

One thing to bear in mind that the Arctic is in the middle of its polar night, a period of perpetual darkness that occurs above 23.44º latitude, meaning this warming trend is not directly related to exposure to sunlight, but is entirely due to warmth being circulated from further south.