Climate components in the Arctic

The Arctic is characterised by distinct components consisting of water in frozen form: glaciers, snow, permafrost and iced-over water. These components together form the cryosphere. All parts of the cryosphere are sensitive to climate change, and they all play important roles in the global climate system.

Sea ice

Arctic summer sea ice extent

Arctic summer sea ice extent Figure: Panel b i Figure SPM3 fra IPCC Summary for Policy Makers

Sea ice covers large parts of the Arctic Ocean in the winter. Some places are ice-covered year-round, but the edges of the ice cover melt in summer; ice floes break off and float away with the ocean currents. Overall, there is as much as three times more ice in winter than in summer.

The extent of the sea ice cover has decreased sharply over the past 30 years, and the ice is disappearing faster than the climate models have been able to project. The ice is also thinner; less of it is compact, massive multiyear ice. More specifically, the IPPC summary of available knowledge from 2013 shows that the extent of the sea ice has decreased by 3.5 to 4.1% per decade in the period from 1979 to 2012, and the amount of sea ice that has survived at least one summer season has decreased by 9.4 to 13.6% per decade over the same period.[1] 

It is quite certain that these changes in extent of sea ice are happening faster than before, and the fastest changes are seen in the summer and autumn months. The records suggest that the thickness of ice in the Arctic Ocean has decreased by an average of 1.3 to 2.3 metres between 1980 and 2008. In some parts of the Arctic this means that ice-free conditions last up to two months longer. These pan-Arctic trends are apparent also in waters near Norway, the Barents Sea and Fram Strait.

The series of observations reported to MOSJ (Environmental Monitoring of Svalbard and Jan Mayen) show distinctly negative trends in ice coverage throughout the monitoring period. Moreover, although these observations show great variability in the thickness of ice passing through Fram Strait, both the variability and the thickness have decreased in recent years.

Taken overall, the sea ice in the Arctic is expected to continue to have less coverage and be thinner at all times of the year, albeit with regional variations. An ice-free Arctic Ocean in summer may become reality before the middle of this century.

In the global climate system, the area with ice cover will decrease with time owing to altered radiation balance (because of the  albedo effect). This will in turn have impact on other processes and driving forces that set the framework for the global climate.

Changes in sea ice will have impact on the habitat of ice-associated species such as plankton that have evolved to live at the edge of, in, or under the ice, as well as fish, seabirds, seals, whales and polar bears.

Glaciers

The Fifth IPCC Report (2013) summarising available knowledge shows that almost all of the world’s glaciers are shrinking. In the Arctic, Alaska and northern Canada are among the areas where glaciers have lost most ice mass over the past decade. Several parts of the Greenland ice cap have lost mass in the past two decades, and loss of mass is spreading to new parts of this vast ice sheet. The rate of loss is increasing. Surface melting and glacier calving each contribute about half of the loss, and both melting and calving are on the increase. The glaciers are expected to continue to lose mass – somewhere between 15 and 85% before the end of the century, depending on the future RCPs.[1]

Melting glaciers contribute strongly to rising sea level. The average sea level rose about 0.19 m between 1901 and 2010. Glaciers and ice sheets have contributed to this rise. Average sea level is expected to continue to rise, and models predict an increase of 0.53-0.97 metres by 2100. So far, most of the increase has been caused by thermal expansion of seawater: the warmer the ocean, the greater its volume. Melting of glacier ice is the second largest contributor to sea level rise so far, but it can become the main contributor in the future. Changes in mass balance of the Greenland ice sheet are expected to continue contributing toward a rising sea level. 

Ice on rivers and lakes

Of the thousands of lakes and rivers in the Arctic, most are covered with ice at least six months per year. Although there are regional differences in the Arctic, the period when these waters are ice-bound is shorter now than it was 100 years ago. Ice forms later in the autumn, and breaks up earlier in the spring.

Snow

In the Arctic, the ground is covered with snow three quarters of the year. Both satellite observations and observations on the ground show that the snow cover in the northern hemisphere has decreased over time, particularly in the spring. These changes are most obvious in the places that are warmest, but that are nevertheless normally snow-covered for parts of the year. The snow cover in the northern hemisphere will continue to shrink through the rest of this century, by as much as 25% depending on the future RCPs.[1]

Less snow means a longer growing season, and may lead to changes in vegetation, for example more shrubs and less lichen. That means less food for some animals and more food for others. In this way, alterations in snow season have impact on the entire ecosystem. Higher temperatures in the Arctic will also lead to more precipitation falling as rain in the winter months. When rain falls on snow, ice forms on the surface, preventing grazers such as reindeer and musk oxen from reaching forage under the snow. Read more about the effects of climate change on polar ecosystems.

The snow cover, like sea ice, is an important factor in maintaining radiation balance in the global climate system through the albedo effect). Read more about processes and drivers.

Permafrost

Much of the land in the Arctic is permafrost, ground that is permanently frozen; in some places permafrost can also be found under the seabed. Observations and measurements show that the temperature in the permafrost has risen in most places since the 1980s, albeit with large regional differences. In some places the permafrost is now 2°C warmer than it was 20-30 years ago.[2] In parts of Scandinavia and Russia, the active layer of earth that lies atop the permafrost and that thaws in the summer, has become as much as 20 cm thicker,[2] and there have been major reductions in permafrost in the European parts of Russia.[1] The total area of the northern hemisphere with surface permafrost is expected to decrease by as much as 80% by the end of this century, depending on the future RCP.

Thawing permafrost releases greenhouse gases (mainly methane) that are currently “locked” in the ground. When permafrost thaws it will also affect the hydrological cycle in the area. Small lakes and tarns will usually dry out when the permafrost thaws and their water drains away.

References

  1. Intergovernmental Panel on Climate Change (IPCC) 2013. Fifth assessment report contribution.
  2. Arctic Monitoring and Assessment Programme (AMAP), 2012. Arctic Climate Issues 2011: Changes in Arctic Snow, Water, Ice and Permafrost. Snow, Water, Ice and Permafrost in the Arctic (SWIPA) 2011 Overview Report.