Which one among the following is the primary environmental concern associated with permafrost thawing in the Arctic ?

Correct — B, (b) Release of Methane and Carbon dioxide. What makes permafrost thaw a global problem rather than a regional one is the carbon locked inside it.

Permafrost is ground that has stayed at or below the freezing point for at least two consecutive years, and much of the Arctic's has been frozen for thousands. Buried in it are the remains of plants and animals that died over that time and never fully decayed, because decomposition all but stops in frozen ground. The store of organic carbon held this way across the northern permafrost region is estimated in more than a thousand gigatonnes — more carbon than the atmosphere itself currently holds.

Thaw restarts the biology. Once the ground warms, microbes resume breaking down that ancient organic matter. Where oxygen is available the product is CARBON DIOXIDE; in waterlogged, oxygen-poor ground — thaw lakes and boggy hollows — the product is METHANE. Methane matters out of proportion to its quantity because, molecule for molecule, it traps far more heat than carbon dioxide over the decades after release.

And that is what makes this the PRIMARY concern: it is a feedback. Warming thaws permafrost; thawing releases greenhouse gases; those gases add to the warming that thaws more permafrost. The carbon involved is not part of the annual biological cycle — it has been out of circulation for millennia — so its return is an addition to the system rather than a transfer within it. The other options in this set describe real consequences of a warming Arctic, but they are effects felt in a region; this one changes the global budget.

Why the others are wrong

• (a)Displacement of the indigenous communities — A real and serious consequence, and not to be dismissed: as permafrost thaws the ground subsides, buildings, roads, pipelines and airstrips built on frozen soil tilt and fail, and coastal settlements lose land to erosion, forcing communities to move. It is nevertheless a human and regional effect, and the question asks for the primary ENVIRONMENTAL concern — the one that acts on the climate system as a whole. That is the greenhouse gas release, which is also what drives the subsidence in the first place.
• (c)Spread of invasive species — Warming does let species move poleward, and shrubs advancing into tundra is a documented change. But this follows from the Arctic getting warmer generally, not from the thawing of frozen ground specifically, and it is nobody's account of why permafrost thaw is watched so closely. Test each option by asking what it has to do with the THAWING PROCESS itself, and this one is only loosely connected.
• (d)Increase of UV radiation — Belongs to a different environmental problem altogether. Ultraviolet radiation reaching the surface increases when stratospheric OZONE is depleted, which is caused by chlorofluorocarbons and related halogenated compounds and is addressed by the Montreal Protocol. Permafrost thaw releases carbon dioxide and methane, which are greenhouse gases and do not destroy ozone. Ozone depletion and global warming are the two most commonly confused environmental issues in these papers.

Permafrost underlies a large fraction of the land in the Arctic and subarctic — Siberia, northern Canada, Alaska and Greenland — and also occurs at high altitude, including in the Himalaya. Above it lies an ACTIVE LAYER that thaws each summer and refreezes each winter; the permafrost proper stays frozen year-round. When the active layer deepens and the frozen ground below begins to thaw, the ice within it melts, the ground loses volume and slumps, producing the pitted, water-filled landscape called thermokarst. Microbial decomposition of the exposed organic matter then releases carbon dioxide and, under waterlogged conditions, methane. The consequences run from the local — collapsing infrastructure, coastal erosion, changed drainage — to the global carbon budget, where the permafrost store is one of the recognised feedbacks capable of amplifying warming.

Key facts

• Permafrost is ground that remains at or below 0 degrees Celsius for at least two consecutive years.
• The seasonally thawing layer above it is the active layer.
• Northern permafrost holds more than a thousand gigatonnes of organic carbon, exceeding the carbon currently in the atmosphere.
• Thawing allows microbes to decompose that carbon, releasing carbon dioxide in aerobic conditions and methane in waterlogged, anaerobic conditions.
• Methane traps far more heat per molecule than carbon dioxide over the decades following its release.
• The process is a positive feedback: warming causes thaw, thaw releases gases, the gases cause further warming.
• Thaw also causes ground subsidence and thermokarst, damaging buildings, roads and pipelines and accelerating coastal erosion.
• Ozone depletion, which increases ultraviolet radiation at the surface, is a separate problem caused by chlorofluorocarbons and governed by the Montreal Protocol.

Common traps

• Choosing a true but local effect when the question asks for the primary one.
• Importing ultraviolet radiation into a greenhouse-gas question.
• Overlooking methane because carbon dioxide dominates the general discussion.
• Treating permafrost carbon as part of the ordinary carbon cycle; it has been out of circulation for thousands of years.

• practice — not a real PYQ

  The layer of ground above permafrost that thaws each summer and refreezes each winter is known as which one among the following ?

  • (a)The active layer
  • (b)The talik
  • (c)The regolith
  • (d)The moraine

  Answer(a) The active layer

• practice — not a real PYQ

  Methane is released rather than carbon dioxide when thawed organic matter decomposes under which one among the following conditions ?

  • (a)Dry and well aerated conditions
  • (b)Waterlogged and oxygen-poor conditions
  • (c)Strongly acidic conditions only
  • (d)Conditions of intense ultraviolet exposure

  Answer(b) Waterlogged and oxygen-poor conditions