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D4.3.3—Boreal forest tipping point

Boreal forests face tipping-point risk when warming, drought, fire, pests, and decomposition shift them from carbon sinks to carbon sources.

Syllabus
First assessment 2025
Objective
D4.3.3
Level
SL

Exam analysis

Chance of appearing1%of analysed past papers
Latest appearanceNovember 2018
Most common paperPaper2
Typical marks2

Common command terms

  • Explain

Recent exam appearances

November 2018Paper2 ["SL"] · TZ03(c)[ 2 ]D4.3.3—Boreal forest tipping point
Practice this objective

Coverage 2018–2018 · Updated 16 Jul 2026

Boreal Forests Can Shift from Carbon Sink to Source

A boreal forest tipping point can occur when carbon uptake by growth falls below carbon released by mortality, decomposition and fire.

Warmer temperatures + reduced winter snowfall → drought stress → lower taiga primary production and forest browning → more frequent/intense fires → combustion of living biomass and legacy soil carbon → net carbon loss.

Released carbon strengthens warming, while tree loss reduces future uptake; these feedbacks can make recovery to the former forest state difficult.

Repeated severe fires can burn older stored carbon as well as current vegetation, while drought prevents conifer regeneration from replacing the lost sink.

A tipping point is a risk of persistent state change, not a precisely dated outcome for every boreal region; local moisture, species and management matter.

Boreal forest tipping point

Assessment in practice

2 marks
How it is assessed

This objective is assessed through structured response, commonly using Explain.

Command terms

Explain

What earns marks

Build the answer around this relationship: Boreal warming can increase drought, fires, pests, disease, and tree mortality.

Representative question

Question 1

[Maximum number: 2]

An increase in global temperatures poses a critical threat to boreal forests. Explain the consequences of climate change to this northern ecosystem.

Retrieve the SL Climate Chain

Core D4.3 is secure when every climate impact is explained as a chain: human greenhouse-gas sources or feedbacks change climate conditions, which alter habitats, oceans, carbon stores, or species distributions. Carbon sequestration is the mitigation chain that stores atmospheric CO2.

  • human gases and positive feedbacks amplify warming
  • boreal forests, ice habitats, upwelling and reefs shift through specific mechanisms
  • species may move poleward, upslope, contract, or lose ice/reef habitat
  • afforestation, agroforestry, regeneration and peatland rewetting store CO2

Climate Effects on Ecosystems

Core climate-change transfer answers should not list endangered examples. They should identify the climate driver, explain the physical or chemical mechanism, then state the biological consequence. Use this for greenhouse gases, feedbacks, boreal forests, ice-dependent species, upwelling, range shifts, reefs, and carbon sequestration.

  • Link human activities to increased greenhouse gases and enhanced warming.
  • Explain ecosystem impacts using mechanisms such as positive feedback, carbon sink/source shifts, habitat ice loss, reduced upwelling, range shifts, bleaching or acidification.
  • Explain carbon sequestration by naming the storage pathway in biomass, forests, soils or peatlands.

Concept essentials

  • Boreal warming can increase drought, fires, pests, disease, and tree mortality.
  • Faster decomposition and permafrost thaw can release carbon stored in cold soils.
  • A tipping point occurs when feedbacks shift the forest into a different, less stable state.