It was a remarkably cold winter across the high Arctic, at least compared to the abnormally mild winters in many recent years. But the weather pattern has reversed this spring and unusually warm air is now surging toward the North Pole, paving the way for the Arctic ice melt season to commence.
The sudden pulse of warmth is one of many observed in the Arctic in recent years, which research shows are increasing in frequency due to rapid climate change, accelerating the loss of sea and land ice.
Above freezing temperatures are showing up in the Central Arctic about one month earlier than average this week, according to Ted Scambos, a senior research scientist at CIRES, an atmospheric research institute operated by the National Oceanic and Atmospheric Administration and the University of Colorado at Boulder.
Computer model projections show mild weather anomalies covering a vast expanse, stretching from the Barents and Kara seas near Siberia (which itself is unusually mild for this time of year) to the Chukchi Sea off the Alaska coast. These anomalous readings are reflected in the average temperature over the high Arctic (north of 80 degrees latitude), which has spiked in recent days, rising over 12 degrees (7 Celsius).
This unusually mild air mass is expected to continue for at least the next seven to 10 days, possibly longer, computer model projections show. A high pressure area parked over the Central Arctic will also ensure clear skies, which is a key ingredient in warm season extreme melt events due to feedback loops involving the melting of snow and sea ice.
Scambos says the weather this week could cause the snowpack on top of the sea ice to "ripen" early in the season, which would cause the snow to get some liquid meltwater in it, lowering its reflectivity, or albedo, and absorbing more incoming solar energy.
“This early start can be critical because the sun is very high in the sky, (there is) lots of solar energy available (if skies are clear). The current heat wave is associated with a high pressure area right over the Arctic, so the sunshine is pouring onto the far north right now unfortunately, things could be off to a fast start,” Scambos said in an email.
According to Ruth Mottram, a climate scientist at the Danish Meteorological Institute, the temperature Tuesday in Kangerlussuaq, Greenland, was significantly warmer than large parts of Denmark. However, the unusually mild weather across the Arctic this week is not expected to result in a major melt spike on the Greenland Ice Sheet, she said, since the greatest temperature anomalies will be situated over the Central Arctic, including the North Pole.
Beause of coronavirus-related travel restrictions, scientists will not be venturing out onto the ice sheet this summer, and instead conditions there will be monitored mainly via satellites and fixed surface instruments. The lack of a research season will set some field projects, particularly those that are drilling ice cores to investigate past climate conditions and study how glaciers are melting in various parts of the world's largest island, back considerably.
“Greenland ice sheet melt has been creeping up a little over the last week, but it’s not really significantly underway yet, and I wouldn’t necessarily expect it to be,” Mottram said via email. About 3% of the ice area was melting Tuesday, mainly in southwest Greenland.
"We define the melt season start as three days in a row with more than 5% of the ice sheet surface area melting at least part of the day, and this can happen at any time from now on basically," Mottram said.
“It wouldn’t be particularly unusual for it to start this week — the average start date is late May but it can be as early as mid-April and as late as early June. The melt season is often kick-started by warm weather and then stalls if it gets colder again afterwards.”
According to Mottram, the ice sheet has a below average surface mass balance due to lack of snowfall in some areas this winter. The mass balance is a way of accounting for the gains from winter snows compared to losses from summer melting. A negative surface balance means the ice is losing more mass than it is gaining in a given year.
“This typically means that if we get long periods of warm weather and clear skies over Greenland, the snow will quickly melt exposing the glacier ice below and then the albedo melt feedback will kick in and accelerate melt earlier — essentially, this is what happened last year when the melt season started on the 29th April but really got going with early warmth from mid-May onwards.”
Zack Labe, a graduate student at the University of California at Irvine who studies Arctic climate change, put the current warmth in the context of long-term climate change. April, for example was the warmest on record globally, powered largely by warming in the high latitudes, including in particular the Russian Arctic, according to NASA data released Wednesday.
"The duration and intensity of the warmth (relatively-speaking) across northern Siberia has really been incredible this year," Labe wrote in an email. "Eurasion snow cover is notably below average too."
Labe said ice and snow melt is likely to accelerate this week in the East Siberian, Kara and Laptev Seas and that the ice in the Kara Sea is already below average for this time of year.
On global maps of temperature anomalies for the year so far, northern Siberia shows up as a splotch of crimson red, with some of the largest anomalies of anywhere in the world. Across parts of northern Asia, average temperatures so far this year have been 5.4 degrees above average or higher, according to a report released Tuesday by the National Oceanic and Atmospheric Administration.
Unsurprisingly, despite changes in day-to-day weather, including the relatively cold winter that just ended, the Arctic continues to dramatically warm in the long term. The region is warming at more than twice the rate of the rest of the globe, with impacts manifesting themselves in increasingly disruptive ways, including thawing permafrost cover, melting sea ice and melting glaciers.