Climate change and tundra ecosystems

Overview

Already happening to permafrost as the climate warms and permafrost carbon feedback.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   Why is the Arctic warming faster than the rest of the planet?

   Model answer

   Because of Arctic amplification, in which feedbacks concentrate warming at high latitudes; the Arctic has warmed at roughly two to four times the global average rate. The most important mechanism is the ice-albedo feedback: as bright, highly reflective snow and sea ice melt, they expose dark ocean water and dark tundra vegetation, which absorb far more solar radiation than they reflect, which causes further warming and further melting. In addition, the shallow, stable Arctic atmosphere traps added heat near the surface rather than mixing it upwards, less energy is used in evaporation in the cold, and warmer air and ocean currents transport additional heat polewards.

2. 2

   What is already happening to permafrost as the climate warms?

   Model answer

   Permafrost temperatures have been rising measurably at monitoring boreholes across the Arctic, the active layer that thaws each summer is deepening, and the southern boundary of continuous permafrost is retreating northwards so that continuous permafrost is becoming discontinuous. Where ice-rich ground thaws, the volume of the ground shrinks and the surface subsides irregularly, producing thermokarst - hummocky, pitted ground, slumps and landslides on slopes, and new lakes that form in the hollows and can later drain abruptly when their outlet thaws. These are observed changes, not projections.

3. 3

   What is the permafrost carbon feedback, and why is it a global concern?

   Model answer

   Arctic permafrost holds an enormous quantity of organic carbon, accumulated over thousands of years as plant material that froze before it could decompose, and current estimates put it at roughly twice the carbon presently in the atmosphere. As the ground thaws, this material becomes available to microbes and decomposes, releasing carbon dioxide where conditions are dry and aerobic and methane where they are waterlogged and anaerobic. Methane is a far more powerful greenhouse gas than carbon dioxide over short timescales. These emissions add to atmospheric greenhouse gas concentrations, causing further warming and further thaw, so it is a positive feedback that amplifies global warming rather than a local effect. It is a concern precisely because it is largely irreversible on human timescales and is not fully accounted for in emissions budgets, though the rate and total scale of the release remain uncertain.

4. 4

   What is shrubification, and why is it happening?

   Model answer

   Shrubification is the observed expansion of dwarf shrubs such as willow, birch and alder across areas of tundra formerly dominated by mosses, lichens, sedges and low herbs, and their increase in height and density. It is happening because warmer summers lengthen the growing season, a deeper active layer allows deeper rooting and greater nutrient uptake, and faster decomposition in warmer soils releases nitrogen that was previously locked in frozen litter, which favours faster-growing woody species over slow-growing lichens. Satellite records show a widespread greening of the Arctic as a result. Shrubs then trap snow, which insulates the ground and warms it further, and their dark canopy lowers the albedo, so the change reinforces itself.

5. 5

   How is climate change affecting tundra animals?

   Model answer

   Ranges are shifting northwards, so boreal species such as moose, red fox and beaver are moving into tundra and displacing or preying on Arctic specialists such as the Arctic fox, which has nowhere further north to go. The timing of plant growth is advancing faster than the migration and calving timing of grazers such as caribou and reindeer, so herds arrive after the most nutritious growth has passed, a mismatch that reduces calf survival. Rain-on-snow events, which are becoming more frequent as winters warm, form a layer of ice over the ground that seals lichens and other forage beneath it and has caused mass starvation of reindeer and musk oxen. Loss of sea ice reduces the hunting platform of polar bears and the haul-out ice of seals and walruses. Thawing ground drains some wetlands used by breeding waders and wildfowl while creating others, and warmer conditions allow insect pests and parasites to spread.

6. 6

   What other physical changes to the Arctic landscape are being caused by warming?

   Model answer

   Coastal erosion has accelerated sharply, because sea ice no longer protects the shore for much of the year, so waves and storms now reach cliffs of frozen sediment which thaw and collapse, and some coasts are retreating by many metres a year. Snow is melting earlier in spring and lying for a shorter part of the year, and glaciers and ice caps are losing mass. Rivers are breaking up earlier and their regimes are shifting. Ground that has lost its ice becomes unstable, so slopes fail and gullies develop. Tundra wildfires, once rare, have become more frequent as the surface dries in warmer summers, and they burn the insulating peat layer and expose the permafrost beneath.

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