Melting permafrost causes a rise in sea levels, redistribution of fresh water pools and changes in land forms. Seasonal thawing over stable permafrost results in the predictable formation of pools and saturated soil necessary to maintain the existing tundra and marsh ecosystems. As the permafrost thaws, the land shifts to form arid raised areas and pits prone to flooding called thermokarst, neither of which are conducive to the existing ecosystems. Additionally, new rivers formed by thermokarst frequently contain high levels of sediments and silts, which degrade water quality and endanger fish and birds.
Stable permafrost limits the movement of groundwater, which keeps plant roots shallower than in warmer climates. When permafrost melts, the groundwater is released, which floods the area and causes erosion and landslides. Because vegetation roots are shallower, plants and trees in frigid regions are especially vulnerable to soil changes. As permafrost is melting, boreal forests are shrinking due to fallen trees and changes in soil characteristics. Grasslands and wetlands are replacing forests and tundra.
These habitat changes have a significant impact on species distribution in affected regions. Regions see a loss of habitat for mammals, such as caribou, and terrestrial birds, but a gain for aquatic animals and birds. For example, erosion due to melting-permafrost-induced soil changes blocks rivers and streams, which prevents salmon from spawning.
Thawing of permafrost results in warmer soil, which speeds decomposition of plant and animal matter that has been locked in the ice for many years. The thawed soil then releases the products of decomposition, carbon dioxide and methane, into the atmosphere. As both of these are greenhouse gasses, the fear is that their rapid release as permafrost melts will substantially contribute to increases in global temperatures. This will then speed up the current global climate change trends, resulting in more rapid melting of permafrost and contributing to an increasingly rapid cycle of climate change.