Major decline in sea-ice concentration has begun to slow

14 August 2020

The rapid rate of ice loss observed in early July continued in the third week of the month, before dropping again rapidly (Figure 4).

The mean sea-ice extent in July 2020 was 6.85 million km2 – the lowest extent for the month of July ever recorded by satellite (see Figures 1 and 2). The level was roughly 2.5 million km2 lower than the July monthly mean for the years 1981 to 2010 and circa 280,000 km2 lower than the previous record low in July 2019 (see Figure 2). During the course of the month, the sea ice shrank by an average of 106,000 km2 per day, which is roughly 17,000 km² more than the 86,800 km² per day recorded from 1981 to 2010. This equates to a total reduction in sea-ice extent of 3.07 million km2 in July 2020.

The linear rate of sea-ice extent loss for the month of July, including 2020, is 8.5 % per decade, or roughly 80,000 km2 per year. This represents an area roughly the size of Bavaria. In the 42 years of satellite observation, the mean Arctic sea-ice extent for July has decreased by about 3.47 million km2, based on the difference between the linear trends in 1979 and 2020.

Higher-than-average air temperatures and the extensive formation of meltwater pools contributed to the sea-ice extent remaining at a record low for the month of July. Towards the end of the month, a low-pressure system settled over the ice in the Beaufort Sea region. Above all, the waters of the East Siberian Sea, Laptev Sea and Kara Sea were dominated by open water. Overall, the sea-ice extent in large parts of the Arctic was significantly below the long-term average (see Figure 3).

The unusually early sea-ice retreat on the Siberian side of the Arctic meant that, in the second half of the month, the Northeast Passage was ice-free (see Figure 4); this is the earliest time in the year that it has ever been ice-free. Though ice could still be found around the Severnaya Zemlya archipelago, it gradually disappeared in early August. The Northeast Passage is expected to remain open and ice-free for the next two to three months.

While the ice rapidly retreated in the first three months of July and was below the curve for 2019, from 23 July this process slowed as the retreating ice edge passed into regions with a greater ice concentration, where the ice didn’t melt as readily. Nevertheless, a new lowest minimum sea-ice extent for the month of July since the beginning of satellite observation was recorded in July 2020.

In July, the average air temperature at 925 hPa (ca. 760 m above sea level) was up to 6°C higher than the long-term average over the central Arctic  Ocean near the Pole (Figure 6, left). In the coastal regions, temperatures were between 2°C and 4°C above the long-term average. Above-average air temperatures spread further south over Baffin Bay and Davis Strait. One exception to the rule: the southern Beaufort Sea, where temperatures were roughly 1°C to 2°C below the long-term average. The warm conditions in the first half of July continued through the rest of the month. This temperature pattern reflects the unusually high atmospheric pressure at sea level over the Laptev Sea, East Siberian Sea and Greenland, which allowed warm air to spread to the coastal regions.

Onset of melting and formation of meltwater pools

The point when melting starts and meltwater pools begin to form influences how much sea ice will melt in summer. Melting snow and meltwater pools reduce the ice’s surface albedo, which leads to more solar energy being absorbed. In just the same way, the early formation of open water allows the ocean to absorb more sunlight, which warms the mixed layer, and in turn promotes further bottom and lateral melting.

This summer, the onset of melting was earlier than average in almost the entire Arctic Ocean with the exception of the southern regions of the Beaufort and Chukchi Seas, parts of the East Siberian Sea and the southern Hudson Bay. In the Laptev and Kara Seas, melting began up to 30 days earlier that the long-term average. The early onset of melting was linked to a prolonged high-pressure area over Siberia in April and May, and record-breaking high spring temperatures in the region. The early onset of melting on the Siberian side of the Arctic could be seen in the extensive meltwater pool formation in the East Siberian Sea, Laptev Sea and parts of Kara Sea in May. In June, the meltwater pools were more extensive than average over large parts of the Arctic Ocean, and especially north of Greenland and the Canadian Arctic Archipelago. The development of extensive meltwater pools in the East Siberian Sea and Laptev Sea early in the season promoted the early development of open water in this region. At the same time, the ice in the area was probably relatively thin due to the strongly positive Arctic Oscillation during the winter. The atmospheric circulation from land to sea in the spring and early summer also contributed to the early ice retreat in the region. (Source: nsidc.org/arcticseaicenews/2020/08/steep-decline-sputters-out/)




Contact:
Dr. Georg Heygster (Universität Bremen)
Dr. Renate Treffeisen (AWI)

Questions?
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