Areas with lowland permafrost are likely to shrink in northern Sweden. Warmer summers and more winter precipitation are two of the reasons. This is shown in a new dissertation from Lund University in Sweden.
Permafrost is ground that is frozen year round at least two years in a row. North of the Arctic Circle permafrost is common due to the cold climate. For several years, physical geographer Margareta Johansson at Lund University has studied lowland permafrost in peat mires surrounding Abisko. Permafrost is on the edge of its range there. Johansson states that permafrost is being affected by climate changes.
“At one of our sites, permafrost has completely disappeared from the greater part of the mire during the last decade,” she says.
In areas where permafrost is thawing the ground becomes unstable and can collapse. This can be a local and regional problem in areas with cities and infrastructure. Moreover, the thaw can cause increased emissions of the greenhouse gases carbon dioxide and methane from the ground. Roughly 25 percent of all land surface in the northern hemisphere are underlain by permafrost.
The thawing of permafrost that occurs today is likely to continue, in Margareta Johansson’s view. She regards it as probable that there will be no permafrost in lowland areas around Abisko in 50 years.
“With the present climate it is likely that the changes seen in permafrost in the Abisko area will also occur in other areas, and my study can therefore provide a basis for studies in other geographic areas that are next in line,” she says.
Margareta Johansson’s research shows that the permafrost in the Abisko area is thawing both from above and from below. From above it is thawing primarily because the summers have become warmer and because the snow cover has become thicker in winter. A thicker snow layer acts as an insulating blanket, which means that the ground does not get as cold as it would under a thinner layer of snow.
From below the permafrost is thawing probably as a result of greater mobility in the groundwater. Margareta Johansson explains that the annual precipitation of both rain and snow has increased dramatically during the last decade. More rain and more melted snow create more movement down in the groundwater, which thaws the permafrost. Between 1997 and 2007 a total of 362 millimeters of precipitation fell annually in Abisko, which is a 20-percent increase compared to the mean annual precipitation for the years 1961 and 1990.
The dissertation will be presented and defended at Lund University on February 26, 2009.
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