RAS question
Which of the following correctly describes 'permafrost thawing' as a climate feedback mechanism?
Correct answer: (B) A positive feedback where thawing releases stored CO2 and methane, further warming the atmosphere.
Permafrost thawing is a positive climate feedback in which warming thaws frozen ground, releasing stored carbon as CO2 and methane that further warm the atmosphere.
Explanation
Permafrost is ground that remains frozen year-round. It is a major Northern Hemisphere carbon store, and NASA explains that as climate warms, frozen soil carbon can enter the atmosphere. Once thawed, microbes decompose organic matter and produce CO2 and methane, both greenhouse gases. This makes option B a positive feedback: warming causes thaw, thaw releases gases, and those gases add to warming. NASA also notes that thermokarst lakes can speed thaw and methane release from Arctic soil, so this is not just local melting with no wider climate relevance; it is an amplifying carbon-cycle feedback.
Why the other options are wrong
- (A) Permafrost thawing does not absorb CO2 as a negative feedback; thawed soil releases CO2 and methane into the atmosphere.
- (C) The process is not Antarctic-only or climate-neutral, because major permafrost regions occur in Arctic Siberia, Alaska and Canada, and NASA discusses its role in the global carbon budget.
- (D) Thawing permafrost does not only release water vapour; the key gases are CO2 and methane, which strengthen warming rather than cool Earth by reflecting sunlight.
Concept
This tests climate feedback mechanisms within Environment and Ecology, especially how cryosphere change interacts with the carbon cycle. It recurs in RAS because global warming, greenhouse gases and Arctic change are standard climate-change application areas.