This year has seen some exceptionally low extents of Arctic sea ice as well as periods of much higher than usual temperatures in the region.
Ed Blockley manages the Met Office Polar Climate group, whose responsibilities include monitoring the increases and decreases of Arctic sea ice. Commenting on the current state of sea ice he said: “Sea ice extent in the Arctic is at an unprecedented low value, and 2016 has been a notable year in particular.”
Throughout the year, the extent of sea ice in the Arctic rises and falls, approximately following the seasons. During March climate scientists expect to witness the greatest extent of Arctic sea ice, the so-called winter maximum, while the corresponding summer minimum occurs during September. Satellite measurements of Arctic sea ice extent have been taken regularly since 1979.
Ed Blockley said: “This March we witnessed the lowest winter maximum on record of 14.52 million square kilometres. This was followed by a mild spring and a record low monthly extent for May. The summer minimum in September wasn’t at record-breaking levels but at 4.14 million square kilometres it was notably low, as it was the joint second lowest year on record after 2012.”
Although the September event was noteworthy, it is what has happened since which has been causing concern for scientists. Ed Blockley added: “After the minimum, the extent of sea ice started to increase as more ice began to form. Around 1st October the freeze slowed down considerably and by the third week in October the extent was lower than it was at this point in 2012 – the year with the lowest September minimum on record.
“Since then Arctic sea ice extent has been at unprecedented record low levels for the time of year.”
Met Office forecasts over the middle of November show some relatively high temperatures in the Arctic which are supported by those observed temperatures available in the region. In particular on the 16 November we were forecasting temperatures above -5°C over most of the Eurasian Arctic and of over zero Celsius in the Barents Sea as far north as Svalbard. Temperatures this warm in November are up to 20°C above the long-term average.
Commenting on these temperatures, Ed Blockley said: “Daily average temperatures measured at Svalbard airport over October and November have been between around 5 and 13°C above the long-term (1981-2010) average. The daily maximum and minimum temperatures recorded over November have also been higher than normal and have been close to record November highs for about half of the month so far.
“November 2016 has been very warm in Svalbard and as things stand, if the remainder of the month continues to be this warm, then 2016 could very well overtake 2009 to become the warmest November on record there.”
There is quite a lot of daily variability in the temperatures recorded in Svalbard because the air temperatures depend heavily on which direction the wind is coming from and hence whether it passes over sea ice, snow-covered land, or open ocean. At present the sea ice is very low and the ocean surface relatively warm around Svalbard.
Speaking about the impacts of these temperatures on Arctic sea ice, Ed Blockley continued:
“Between 16 and 20 November 2016 the total Arctic sea ice extent actually declined, instead of there being net freezing over the Arctic as would be expected. Although extraordinary this is not unprecedented as a similar, although smaller, reduction in Arctic-wide extent was observed at the start of November 2013. The decline this year resulted from a reduction of the ice cover in the Barents Sea – in the North Atlantic sector – and the Bering/Chukchi Sea – on the Pacific side. This seems to have been caused by relatively warm and moist air being transported into the region from the south.”
Near-surface air temperatures in the Arctic are unusually warm at present, as they have been for the entire autumn. Some forecasting centres have reported observations of up to 20°C warmer than normal. Ed Blockley added: “This will have been partly caused by there being reduced cooling of the atmosphere from the surface because there is less sea ice, meaning that air has more contact with the relatively warm ocean. The sea ice extent is currently at a record low level in the Arctic and the sea surface temperatures are up to 3°C Celsius above normal.
This autumn has seen some rather unusual patterns of atmospheric circulation in the Northern Hemisphere. Persistent southerly winds have brought warmer air northward into the Arctic from both the North Atlantic and across the Bering Straits from the North Pacific.
As well as causing the ice to melt by increasing the surface air temperature, this persistent southerly flow has also acted to push the ice northwards preventing it from advancing to lower latitudes.
Commenting on the future state of Arctic sea ice this season, Ed Blockley added: “This decline is most likely not going to continue, and in fact the most recent observations show ice extent increasing slightly again. Over the whole winter more ice will be formed but this warm spell means that it is possible there will be less ice in the Arctic at the end of winter.”
Looking at longer term trends, September or summer Arctic sea ice extent has decreased by over 13% per decade since satellite records began in 1979. This is the equivalent to losing an area of sea ice greater than the size of Scotland each year. With this trend in mind, there is widespread speculation about the date when the Arctic will be ice-free in the summer.
Ed Blockley said: “The events happening now don’t mean that the ice will all be gone next year because the rate of melt is highly dependent on the weather conditions that occur in the Arctic in summer. However it will mean that the Arctic sea ice will start the melt season from a disadvantaged position and so would be more susceptible to melt if the conditions are right for it. The latest estimates from the Intergovernmental Panel on Climate Change (IPCC)’s Fifth Assessment Report (AR5) are that we may see the ‘ice-free’ Arctic summer minimum in the 2030s.”