Permafrost is ground that stays frozen for at least two years in a row, and in many Arctic regions it has remained frozen for thousands of years. It can contain soil, rock, ice, dead plants, and trapped gases. As air temperatures rise, the upper layers of permafrost thaw more deeply during warm seasons.
This matters because thawing ground can reshape landscapes, damage buildings and roads, and release greenhouse gases.
Key Facts
- Permafrost = ground at or below 0°C for at least 2 consecutive years.
- Active layer = surface layer that thaws in summer and refreezes in winter.
- Greater air warming causes a deeper active layer and more ground ice melt.
- Organic matter + thaw + microbes can produce carbon dioxide and methane.
- Methane has a stronger short-term warming effect than carbon dioxide.
- Thermokarst forms when ice-rich permafrost thaws and the ground surface collapses.
Vocabulary
- Permafrost
- Permafrost is soil, sediment, or rock that remains frozen for at least two consecutive years.
- Active layer
- The active layer is the surface layer above permafrost that thaws during warm months and refreezes during cold months.
- Thermokarst
- Thermokarst is uneven, collapsed terrain that forms when ground ice melts and the soil surface sinks.
- Methane
- Methane is a greenhouse gas, CH4, that can be produced when microbes break down organic matter in wet, oxygen-poor thawed soil.
- Carbon feedback
- A carbon feedback is a process in which warming releases carbon gases that can cause even more warming.
Common Mistakes to Avoid
- Thinking permafrost is the same as snow or glacier ice. Permafrost is frozen ground, and it may contain soil, rock, plant material, and ice rather than being a sheet of pure ice.
- Assuming permafrost only matters in remote Arctic areas. Thaw can affect global climate through greenhouse gas release and can damage roads, pipelines, homes, and ecosystems in northern communities.
- Forgetting the active layer changes every year. The active layer normally thaws and refreezes seasonally, but long-term warming makes it thicker and can expose older frozen carbon.
- Treating all thawed carbon as methane. Thawed organic matter can release carbon dioxide in oxygen-rich conditions and methane in wet, oxygen-poor conditions.
Practice Questions
- 1 A permafrost site has an active layer depth of 40 cm in 2000 and 64 cm in 2024. What is the average increase in active layer depth per year?
- 2 A thawing wetland releases 12 g of methane per square meter each summer. How much methane is released from 500 m2 during one summer?
- 3 Explain why permafrost thaw can be considered a positive feedback in the climate system, and include the roles of microbes and greenhouse gases.