2.9 Permafrost

Permafrost is frozen ground (soil or rock including ice and organic material) that remains at or below 0°C for at least two consecutive years. They are almost exclusively associated with the Arctic region. It is natural for the topmost layer of permafrost soils to melt when absorbing sufficient heat during summer. In this layer (referred to as the active layer) plants can grow and animals find their food. However, in the absence of global warming, the soil underneath this layer always remains frozen, preserving the organic material including large amounts of carbon and methane. It is estimated that Arctic permafrost contains nearly 1,700 billion tons of carbon, about twice the carbon that is currently in the atmosphere. Paleoclimate studies show the land warming trend to be 3.5 times greater during rapid ice loss events and that extra warming by disappearing sea ice penetrates 1500 Km inland, covering almost the entire region of continuous permafrost. (Lawrence et al. 2008).

Over the last 30 years permafrost warming from 0.5 to 2 ºC has been observed depending on the location (Romanovsky et al. 2008) with the most sensitive regions being the areas exposed to the Arctic Ocean. Since 1900 seasonally frozen ground has declined by 7% in maximum extent. Observed rates of mean annual erosion vary from 2.5 to 3.0 m yr-1 for the ice-rich coasts to 1.0 m yr-1 for the ice-poor permafrost coasts along the Russian Arctic Coast. Over the Alaskan Beaufort Sea Coast, mean annual erosion rates range from 0.7 to 3.2 m yr-1 with maximum rates up to 16.7m yr-1 (IPCC 2007). Permafrost and frozen ground degradation affect the water surface causing retreating of ponds and drier soils in those areas with thin permafrost, whereas in those areas with thicker permafrost, new wetlands will come up. (WWF 2008) Is projected that permafrost’s southern limit shift northward by several hundred km during this century. (ACIA 2006).

Vast amounts of methane hydrates (methane gas encased in ice) are stored in sediments in Arctic continental shelves and warmer temperatures (as in previous major warming periods of Earth’s history) have the potential to bring about methane release. (IPCC 2007; Koven et al 2011; DeConto et al 2012;). In fact, very large scale methane emissions in several parts of the Arctic region have recently been observed (Anthony et al 2012; Kort et al 2012). Permafrost thawing is releasing CO₂ and methane to the atmosphere, which acts as a feedback, causing further global warming. It is estimated that by 2050 the permafrost area will have decreased by 20 to 35% in the Northern Hemisphere and the depth of active layer may increase by 15 to 25% and by 50% and more in the northernmost locations. (IPCC 2007). Permafrost degradation could mean a loss of 1 million Km2 of frozen ground and the release of 900 million tons of carbon to the atmosphere by 2100 (Strom R. 2007).

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