With scientific exploration dating back nearly 150 years, records of the changing Arctic are more extensive than any other major cryosphere region except the European Alps. The Arctic Climate Impact Assessment (ACIA) report of the Arctic Council in 2004 comprised the first comprehensive assessment of climate change in the Arctic, and delivered a dramatic message to the world on the changes already occurring there. The Council expanded this work in the 2011 Snow, Water, Ice, and Permafrost in the Arctic (SWIPA) report.
A key finding from SWIPA was that observed changes in the Arctic had far outpaced any projections from scientific modeling, with loss of sea ice, glaciers, snow cover, and permafrost occurring at rates far more rapid than even the most pessimistic IPCC modeling scenarios. This pace of change has continued, and includes the following recent developments.
Arctic summer sea ice extent has declined by nearly 50 percent since satellite observations began in the 1970s. The 2012 summer minimum broke the previous 2007 record on August 26, and sea ice loss continued through September 16, reaching a low of 3.4 million km2 (compared to 2007’s record low of 4.2 million km2). The 2013 summer minimum of 5.1 million km2 was reached on September 13; it is the sixth lowest on record, and over one million km2 below the 1981-2010 average minimum (Figure 2).
More important than the extent of sea ice is the fact that overall thickness, volume, and age of sea ice has decreased by 80 percent since 1979. Older, thicker multi-year ice used to cover much of the Arctic; today virtually all of the sea ice in the Arctic Ocean is new, from the previous one or two winters, and thus quite thin and vulnerable to melt. Because the ice is very thin, most scientists believe an ice-free Arctic Ocean in summer is inevitable within the next decade or two. When this will occur is mostly a matter of the right combination of weather, wind, and ocean currents combining to create the right conditions in a given year. Any recovery of the ice sheets will require several years of temperatures below those of the past decade.
Sea ice is important due to its albedo effect: the broad expanse of sea ice reflects the sun’s warmth back into the atmosphere, cooling the entire northern hemisphere. Darker ocean will conversely absorb heat and speed melting in the Arctic (including Greenland and northern permafrost regions) as well as overall global warming. Preserving as much sea ice as possible is therefore important to the global climate system and feedbacks such as sea-level rise and permafrost methane release. The last time the Arctic Ocean was regularly ice-free in summer was 125,000 years ago, during the height of the last major interglacial period (the Eemian). Temperatures in the Arctic today are coming close to those reached during the Eemian maximum, when sea level was 4-6 meters higher because of partial melting on both Greenland and the West Antarctic Ice Sheet (WAIS) (Ibid).
Greenland Ice Sheets
Greenland is losing ice mass at much higher rates than those predicted or observed as recently as five years ago. Most of the significant glaciers of the Greenland ice sheet have retreated and thinned, and calving of ice at the edges of glaciers into icebergs has accelerated.
Greenland surface albedo has dropped by as much as 30 percent in some areas (Stroeve, et al. 2013) and surface melting has increased. In 2012, surface melting occurred over virtually the entirety (97 percent) of Greenland, something never observed before since satellite data became available in 1979 (ice core data indicate that widespread melting may have occurred a handful of times in the past 1,000 years). The 2013 melting occurred over approximately 45 percent of Greenland at its peak, twice the 1979-2010 average, despite a late start to the melt season. Loss of ice mass from Greenland increased from about 50 Gt/year from 1995‐2000, to 200 Gt/year from 2004‐2008, to about 350 Gt/year from 2008-2012 (Box et al. 2012). Nearly all land glaciers elsewhere in the Arctic have also lost mass in recent decades, at around 150 Gt/year (especially in North America).
Such extensive melting has many scientists concerned that Greenland’s ice sheet stability, especially along the margins, may be vulnerable to rapid ice loss and sudden disintegration into icebergs (Bassis and Jacobs 2013), though additional surface loss may take many hundreds of years (Goelzer et al. 2013).
Permafrost underlies most of the Arctic land area and extends under parts of the Arctic Ocean near the coastline. Temperatures in the upper layers have risen by up to 2C over the past 2-3 decades, particularly in colder permafrost regions. The extent of soil above the permafrost that thaws each summer has increased from Scandinavia to Arctic Russia west of the Urals, and also in Alaska. The southern limit of permafrost in Russia has moved northwards by 30‐80 km during the same period; and by 130 km in Quebec during the last 50 years. Summer icebreaker expeditions over the past three years have documented large volumes of methane gas bubbling to the surface off the Siberian coastline.
The amount of carbon held in Arctic permafrost remains uncertain, but most scientists estimate that it at least equals the amount of carbon released from anthropogenic sources since pre-industrial times. Methane raises particular concern: SWIPA estimated that a release of just 1 percent of the methane present in permafrost below the seabed of the East Siberian shelf would have a warming effect equivalent to a doubling of the amount of carbon dioxide in the atmosphere. Holding temperatures as low as possible in Arctic permafrost is therefore an issue of global concern.
The Arctic Ocean is particularly sensitive to acidification, because increasing amounts of fresh water entering the Arctic Ocean from rivers and melting ice are reducing the Arctic’s capacity to neutralize acidification. Widespread acidification has already been observed in the central Arctic Ocean and has been documented at monitoring sites across the region, especially in surface waters. Because Arctic marine food webs are relatively simple, its ecosystems are vulnerable to change when key species are affected (Shadwick et al. 2013).
The Arctic and surrounding waters contain the largest fishing waters of the northern hemisphere, resources already under stress from historical overfishing and other environmental stresses. Increasing acidification may also impact these commercial fisheries as well as marine resources that are used by Arctic indigenous people.