Permanently frozen palsa mires can be lost by the end of the century
Palsa mires are permafrost mires that are characterized by peat mounds, called palsas, that remain frozen even in summer. Palsa mires occur in areas characterised by low precipitation, strong winds, thin snow cover, and an average annual temperature below -1 °C.
Using three different climate change scenarios, the key finding of the new study is that environments suitable for palsas will disappear almost entirely from the northern permafrost region by the end of the century if climate change is not mitigated. Even in the most optimistic scenario, up to 75 per cent of the environmental conditions suitable for palsas would be at risk of disappearing, and in the worst case, 98 per cent would disappear.
Based on the results of the doctoral thesis, the occurrence of palsas in the Northern Hemisphere is best explained by soil moisture and climatic factors such as air temperature and precipitation. Palsa mires still remain in northern Canada, Alaska, Iceland, northern Finland, Sweden, Norway, and Western Siberia. The thesis utilised statistical modelling and remote sensing data, and the occurrence of palsas was examined using satellite and aerial images of northern regions.
The layer of peat on top of the frozen cores of palsas is essential, as the peat acts as an insulator and prevents the permafrost, which is necessary for the existence of palsas, from thawing. "The effects of climate change on palsas are complex. For example, increased snowfall would not help palsas to persist, but could even promote their degradation. Although snow protects palsas from solar radiation in spring, it is also a good insulator in winter and prevents deep freezing of the ground, which maintains permafrost and palsas," explains Doctoral Researcher Oona Leppiniemi. "In addition, the more snow there is, the more meltwater is produced. Abundant meltwater keeps the peat on top of the palsas wet longer in the spring. Wet peat conducts heat well, allowing solar radiation to thaw the palsas effectively. If there is little snow and meltwater, the peat dries out more quickly, and dry peat acts as an insulator, protecting the palsas from thawing."
If the future is windier, the snow will be swept away from open areas. However, the wind can also erode the peat layer on top of the palsas, leaving them unprotected in summer and allowing the permafrost to thaw more efficiently.
When palsas formed by the permafrost disappear, the topography of the mire becomes more uniform, and the landscape changes. These changes in the abiotic nature may also have an impact on the biodiversity of the northern environments, as the diverse habitats created by the palsas disappear and organisms lose important areas for growth, feeding, and reproduction. In addition, the degradation of permafrost releases greenhouse gases such as carbon dioxide and methane from peat, which may further accelerate global climate change.
"Sometimes, only a small pond remains after the degradation of palsas. However, often the thawed palsa mire starts to resemble an aapa mire. When palsas degrade, species that thrive in drier growing conditions disappear, and the vegetation of the mire becomes less diverse," Leppiniemi explains.
In Finland, previous surveys in 2023 found that one third of the palsas in Northern Lapland have disappeared compared to the situation in the 1990s. In the new thesis, less than a third of Finland's current palsas were found to be in good state, and the surface area of palsas has decreased by up to 76 per cent since the 1960s.
The results obtained in the dissertation improve our understanding of the environmental factors and changes that affect the occurrence and state of palsas in the future. The results can be used to assess the effects of climate change on global greenhouse gas emissions and to prepare nature conservation strategies for maintaining biodiversity in the north.
In Finland, palsas are found in Lapland in the municipalities of Enontekiö, Utsjoki and Inari. The well-known Iitto palsa mire, for example, is located along the Käsivarrentie road. Finland's current palsas can be viewed at Paikkatietoikkuna.
Learn more about the new dissertation in geography: Leppiniemi, O. (2025). Palsa mires of the Northern Hemisphere: environmental characteristics, degradation, and morpho-ecological state