Fast facts about permafrost
Permafrost is soil and sediment that are frozen more than two consecutive years, while the active layer is the upper part of the soil environment that thaws every summer. In practice, this means that permafrost occurs at an average air temperature of -2°C or colder. Active layer thickness varies with the season, but is 0.3 to 4 meters thick (shallow along the Arctic coast; deep in southern Siberia and the Qinghai-Tibetan Plateau). In the Northern Hemisphere, 24% of the ice-free land area, equivalent to 19 million square kilometer1, is more or less influenced by permafrost. Most of this area is found in Siberia, Canada, Alaska and Greenland.
- In northern Siberia and Canada, the permafrost can extend down to depths of more than 700 meters.
- Permafrost contains 1700 billion tons of organic material equaling almost half of all organic material in all soils1. This pool was built up over thousands of years and is only slowly degraded under the cold conditions in the Arctic. The amount of carbon in permafrost is four times the carbon that has been released to the atmosphere due to human activities in modern time2.
- Arctic temperatures are expected to increase at roughly twice the global rate5. The Intergovernmental Panel on Climate Change (IPCC) will in their fifth report establish scenarios for the future, where the temperature in the Arctic will rise between 1.5 and 2.5°C by 2040 and with 2 to 7.5°C by 2100.
- When the climate becomes warmer, the permafrost layer thaws completely or partially in parts of the landscape. In areas where ice caps are melting and glaciers are retreating, permafrost will again be formed.
- Permafrost does not disappear from Greenland, because the permafrost is more than 100 meters thick in large parts of Greenland. Only the upper 1-2 m of permafrost is threatened by thawing in the coming years.
- Permafrost may include both soil and solid rock. Rocks contain no organic material, while soil contains large amounts of organic material. If soil layers thaw due to global warming, the warming may increase the microbial decomposition of organic material.
- Areas covered by permafrost are often a mosaic of areas with herbaceous plants, ericaceous plants, low scrub with willow bushes, and marshes, ponds and streams. In the areas bordering the Arctic permafrost is common in open forests with tree species such as birch, pine, larch and spruce.
- The plant cover of permafrost in Greenland is dominated by a few hardy and hardy plants such as the Arctic Willow, heather, saxifrages, Dryas and various species of mosses, lichens, grasses and sedges. Under the extreme growing conditions in the high Arctic even 100 year old specimens of Arctic Willow are just a few centimeters high. In Russia, Scandinavia and Canada large areas of permafrost are covered with pine and birch forest. Due to global warming, plant growth in the Arctic increases and the tree line moves north.
- Different groups of microorganisms produce carbon dioxide, methane, nitrous oxide and other greenhouse gases when permafrost thaws. Carbon dioxide is formed by a multitude of fungi and bacteria during break down of old plant material in soil. Methane is formed exclusively by a specific group of archaea (bacteria-like microorganisms) and converted to carbon dioxide by certain groups of bacteria. Nitrous oxide is formed by certain bacteria, which may also convert the nitrous oxide to atmospheric nitrogen (N2).
- Measured over a 100 year period, the warming potential of methane in the atmosphere is 25 times higher than carbon dioxide. Methane formed in deep soil layers may be converted into carbon dioxide by micro-organisms in the upper layer of soil prior to the release from the soil surface to atmosphere.
- No one knows for sure how many tons of greenhouse gases are emitted from thawed permafrost soils, but recently2 it was estimated that 110-231 billion tons of CO2 equivalents (about half from carbon dioxide and the other half from methane) will be emitted by 2040, and 850-1400 billion tons by 2100. This corresponds to an average annual emission rate of 4-8 billion tons of CO2 equivalents in the period 2011-2040 and annually 10-16 billion tons of CO2 equivalents in the period 2011-2100 as a result of thawing permafrost. For comparison, the anthropogenic emission of all greenhouse gases in 2010 is approximately 48 billion tons of CO2 equivalents3. Release of greenhouse gases from thawed permafrost to the atmosphere may increase global warming.
- One gram of soil from the active layer may include more than one billion bacteria cells. If placed along each other, bacteria from one kilogram of active layer soil will form a 1000 km long chain. The number of bacteria in permafrost soil varies widely, typically from 1 to 1000 million per gram of soil4. Most of these bacteria and fungi in permafrost soil can not be cultured in the laboratory, but the identity of the microorganisms can be revealed by DNA-based techniques.
- Permafrost may contain large quantities of ice, which is released as water when the permafrost thaws. This may cause soil collapse and increase transport of solutes, including organic matter, nutrients and pollution, which may be carried long distances by river or sea water.
- Permafrost properties can rarely be assessed from the surface or from satellite images, so it is necessary to drill through the permafrost to measure its distribution and condition.
- A warmer climate and less permafrost can open up a number of advantages for the people of Greenland, e.g. in relation to agriculture and extraction of minerals.
- Tarnocai et al. 2009. Soil organic carbon pools in the northern circumpolar permafrost region. Global Biogeochemical Cycles 23, GB2023
- Schuur et al. 2011. High risk of permafrost thaw. Nature 480, 32-33
- UNEP 2011. Bridging the Emissions Gap. A UNEP Synthesis Report. 56 p. UNEP, Nairobi, Kenya
- Hansen et al. 2007. Viability, diversity and composition of the bacterial community in a high Arctic permafrost soil from Spitsbergen, Northern Norway, Environmental Microbiology 9, 2870-2884 – and additional references in this paper. Yergeau et al. 2010. The functional potential of high Arctic permafrost revealed by metagenomic sequencing, qPCR and microarray analyses. The ISME Journal 4, 1206-1214
- IPCC 2007. Summary for policy makers. In: Climate Change 2007: The physical basis. Working group I contribution to the fourth assessment report of the Intergovernmental Panel on Climate Change (eds. Solomon et al.). Cambridge University Press, Cambridge, UK.
Fakta om permafrost
Permafrost er jordlag og sedimenter, som er frosne mere end to år i træk, mens aktivlaget er den øverste del af jordmiljøet, som tør hver sommer.