What is climate change and how does it relate to ecology in the IB DP Biology curriculum?

Climate change refers to significant changes in global temperatures and weather patterns over time. In the context of IB DP Biology, it is studied under ecology as it affects ecosystems, biodiversity, and the distribution of species. Understanding climate change helps students grasp how living organisms interact with their environment and the impact of human activities on natural systems.

How does climate change impact biodiversity?

Climate change impacts biodiversity by altering habitats, leading to shifts in species distribution and potentially causing extinction for those unable to adapt. Changes in temperature and precipitation patterns can disrupt food chains and ecosystems, affecting the survival of various species. In the IB DP Biology curriculum, students explore these dynamics to understand the broader implications of ecological balance and conservation efforts.

What are the main causes of climate change discussed in IB DP Biology?

The main causes of climate change include the increase of greenhouse gases like carbon dioxide and methane in the atmosphere, primarily due to human activities such as burning fossil fuels, deforestation, and industrial processes. These activities enhance the greenhouse effect, leading to global warming. IB DP Biology examines these causes to highlight the role of human impact on ecological systems.

What role do ecosystems play in mitigating climate change?

Ecosystems play a crucial role in mitigating climate change by acting as carbon sinks. Forests, oceans, and wetlands absorb carbon dioxide from the atmosphere, helping to regulate the global climate. In the IB DP Biology curriculum, students learn about the importance of preserving these ecosystems to maintain their ability to sequester carbon and support biodiversity, which is vital for ecological resilience.

How can studying climate change in IB DP Biology help students contribute to sustainability?

Studying climate change in IB DP Biology equips students with the knowledge to understand the scientific basis of climate issues and the impact of human activities on the environment. This understanding fosters critical thinking and problem-solving skills, empowering students to engage in sustainable practices and advocate for policies that reduce carbon footprints and promote ecological conservation.

Why is "Calling all greenhouse gases 'pollution'." a common mistake in Climate Change?

Why it happens: Conflating natural and enhanced effects. How to avoid it: Natural greenhouse effect is essential for life. The CONCERN is the ENHANCED effect from human emissions.

Why is "Confusing the greenhouse effect with the ozone hole." a common mistake in Climate Change?

Why it happens: Both are atmospheric issues. How to avoid it: Greenhouse = infrared absorption → warming. Ozone hole = UV transmission → skin cancer. Different mechanisms.

Why is "Equating ocean acidification with acid rain." a common mistake in Climate Change?

Why it happens: Similar word. How to avoid it: Acid rain = sulfuric/nitric acids from SO₂/NOₓ. Ocean acidification = CO₂ dissolution into seawater.

IB DP Biology (BI)

Climate Change

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Short Notes - Climate Change

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Detailed Study Notes

Detailed notes on Ecology for IB DP Biology, covering key concepts, explanations, examples, and exam-focused revision points.

Climate Change — IB Biology SL: greenhouse effect, biological consequences, ocean acidification, mitigation

Maps to Theme C (Interaction and Interdependence). Covers the greenhouse effect, the link between CO₂ and global temperature, biological consequences for ecosystems, and mitigation strategies.

At a glance

GREENHOUSE GASES (CO₂, CH₄, N₂O, water vapour) absorb infrared radiation re-emitted from Earth's surface.
ENHANCED greenhouse effect: human emissions raise GHG concentration → warmer Earth.
EFFECTS: rising temperature, melting ice, sea-level rise, more extreme weather, ocean acidification.
BIOLOGICAL effects: species range shifts, phenology mismatches, coral bleaching, biodiversity loss.
OCEAN ACIDIFICATION: CO₂ + H₂O → H₂CO₃ → lower pH → corals and shellfish struggle to form CaCO₃.
MITIGATION: switch to renewables, reforestation, reducing methane, dietary change, carbon capture.
FEEDBACKS (e.g. permafrost methane, ice-albedo) can ACCELERATE warming.

What you’ll learn

Mapped to the IB DP Biology SL subject guide (2025 onwards (first assessment May 2025)).

C4.3.5 — Explain the greenhouse effect.
C4.3.6 — Outline major greenhouse gases and their sources.
C4.3.7 — Describe biological consequences of climate change.
C4.3.8 — Outline mitigation strategies.

The greenhouse effect

Why Earth is warming.

Natural greenhouse effect. Without atmosphere, Earth's average surface temperature would be ~−18 °C — too cold for life as we know it. Atmospheric greenhouse gases trap heat, raising the average to ~15 °C.

Mechanism:

Short-wavelength visible/UV radiation from the Sun passes through the atmosphere and warms the Earth's surface.
The Earth re-emits this energy as longer-wavelength infrared radiation.
Greenhouse gases (CO₂, CH₄, H₂O vapour, N₂O) absorb the infrared and re-emit some downward.
This traps heat near the surface.

Major greenhouse gases.

Gas	Main human sources	Relative potency (per molecule, 100-yr)
Carbon dioxide (CO₂)	Burning fossil fuels, deforestation, cement	1× (reference)
Methane (CH₄)	Cattle, rice paddies, landfill, fossil fuel leaks	~28×
Nitrous oxide (N₂O)	Fertilisers, industry	~265×
Water vapour (H₂O)	Natural; amplifies warming as air warms	—

Enhanced greenhouse effect. Human emissions raise concentrations of greenhouse gases, particularly CO₂ (from ~280 ppm pre-industrial to >420 ppm today). The result is global warming and broader climate change.

Greenhouse gases absorb infrared from Earth's surface.
Enhanced effect: human emissions of CO₂, CH₄, N₂O.
Methane 28× CO₂'s potency per molecule.

Biological impacts and mitigation

From corals to crops.

Biological impacts.

Range shifts. Species move poleward and to higher altitudes as their preferred temperatures shift. Some can't move fast enough or have nowhere to go (e.g. mountaintop species).
Phenology mismatches. Spring activities (flowering, migration, breeding) occur earlier with warming. If species don't shift in sync (e.g. caterpillars emerge before birds arrive to feed chicks), populations decline.
Coral bleaching. Warm water expels symbiotic algae (zooxanthellae) from coral; corals lose colour and starve. The 2016 and 2024 global mass bleaching events damaged much of the Great Barrier Reef.
Ocean acidification. $\text{CO}_2 + \text{H}_2\text{O} \rightarrow \text{H}_2\text{CO}_3 \rightarrow \text{H}^+ + \text{HCO}_3^-$ . Higher [H⁺] (lower pH) reduces availability of carbonate (CO₃²⁻), making it harder for corals, molluscs and plankton to form CaCO₃ shells.
Sea-level rise from melting glaciers/ice caps and thermal expansion of seawater inundates coastal habitats.
Extreme weather (heatwaves, droughts, floods) stresses ecosystems and crops.

Positive feedbacks (amplify warming):

Ice-albedo feedback — melting ice exposes darker ocean/land that absorbs more heat.
Permafrost methane release — thawing permafrost releases CH₄ stored in soil, accelerating warming.
Loss of vegetation carbon sinks — droughts and fires release stored carbon.

Mitigation strategies.

Strategy	Mechanism
Renewable energy (solar, wind, hydro, nuclear)	Avoid emitting CO₂
Energy efficiency	Less fuel burned per unit of work
Reforestation / afforestation	Photosynthetic carbon sink
Reduce methane (manure capture, drained rice paddies, leak reduction)	Cuts potent GHG
Dietary change (less beef)	Lower farm methane + land use
Carbon capture and storage	Sequester CO₂ underground
Behavioural change	Reduced flying, public transport, recycling

International agreements (e.g. Paris Agreement, 2015) target keeping warming below 1.5 °C. Tutopiya schools can use Internal Assessments to investigate local impacts (water quality, biodiversity).

Coral bleaching, range shifts, phenology mismatches.
Acidification disrupts CaCO₃ shells.
Positive feedbacks amplify warming.
Mitigation: renewables, efficiency, reforestation, dietary change.

Quick recap

Greenhouse gases trap infrared.
Enhanced effect from CO₂, CH₄, N₂O.
Biological consequences: coral bleaching, range shifts, phenology mismatches.
Ocean acidification harms calcifiers.
Mitigation: renewables, reforestation, dietary change, carbon capture.

Memorise this

Verbatim phrases, formulae and definitions IB DP mark schemes credit (key for AO1 knowledge marks on Paper 1).

Greenhouse: absorbs infrared
CO₂ ~420 ppm (2024) vs 280 pre-industrial
CH₄ 28× more potent per molecule
Acidification: $\text{CO}_2 + \text{H}_2\text{O} \to \text{H}_2\text{CO}_3$
Mitigation: renewables, reforestation, diet

How it’s examined

Paper 1: MCQ on greenhouse mechanism or impact. Paper 2: 'explain the biological consequences of climate change' (3-6 marks); 'discuss two mitigation strategies'.

Sources: IB Diploma Programme Biology subject guide (IBO, 2023 — first assessment 2025). Last reviewed 2026-05-31.

Take this whole topic with you

Step-by-step worked examples — Climate Change

Step-by-step solutions to past-paper-style questions on climate change, written exactly the way a tutor would explain them at the board.

1How greenhouse gases warm the Earth
Building confidence• greenhouse
Question
Explain the mechanism by which greenhouse gases warm the atmosphere. (3 marks)
Step-by-step solution
1. Step 1
  Short-wavelength solar radiation passes through atmosphere and warms Earth's surface.
2. Step 2
  Earth re-radiates this energy as longer-wavelength infrared.
3. Step 3
  Greenhouse gases absorb infrared and re-emit some downward — trapping heat near the surface.
Answer
GHGs absorb outgoing infrared from Earth's surface and re-radiate it, trapping heat.
2Coral bleaching mechanism
Stretch• coral
Question
Explain how rising sea temperatures cause coral bleaching. (3 marks)
Step-by-step solution
1. Step 1
  Corals contain symbiotic algae (zooxanthellae) that photosynthesise and supply energy.
2. Step 2
  When water is too warm, the algae produce toxic levels of reactive oxygen species — coral expels them.
3. Step 3
  Coral loses its colour and source of nutrition; without re-symbiosis, it starves and dies.
Answer
Heat stress → expulsion of zooxanthellae → coral loses energy supply and colour → bleaching/death.
3Ocean acidification harm
Stretch• acidification
Question
Explain how rising atmospheric CO₂ contributes to ocean acidification and impacts marine life. (4 marks)
Step-by-step solution
1. Step 1
  CO₂ dissolves in seawater: CO₂ + H₂O → H₂CO₃ (carbonic acid).
2. Step 2
  H₂CO₃ dissociates: H₂CO₃ → H⁺ + HCO₃⁻; H⁺ lowers pH (acidification).
3. Step 3
  Increased H⁺ reduces carbonate (CO₃²⁻) availability.
4. Step 4
  Corals, molluscs and some plankton struggle to build CaCO₃ shells → ecological damage.
Answer
CO₂ + H₂O → H₂CO₃ → H⁺; lower pH reduces CO₃²⁻; harms calcifiers (corals, shellfish).
4Compare two mitigation strategies
Stretch• mitigation
Question
Compare reforestation and switching to renewable energy as climate mitigation strategies. (4 marks)
Step-by-step solution
1. Step 1
  Reforestation: increases carbon sinks via photosynthesis; trees store C in biomass and soil.
2. Step 2
  Limitations: limited land; slow growth; vulnerable to fires/disease.
3. Step 3
  Renewables (solar, wind): avoid emitting NEW CO₂ from fossil fuels.
4. Step 4
  Most effective combined — renewables tackle emissions directly; reforestation helps re-absorb existing CO₂.
Answer
Reforestation absorbs CO₂ but is land-limited and slow. Renewables prevent emissions but require infrastructure. Both needed.

Key Definitions and Keywords — Climate Change

Definitions to memorise and the exact keywords mark schemes credit for climate change answers — sharpened from recent examiner reports for the 2026 IB DP Biology SL sitting.

Greenhouse effect
Examiner keyword
Absorption of outgoing infrared by atmospheric gases, warming Earth's surface above what radiation balance alone would give.
Ocean acidification
Examiner keyword
Decrease in ocean pH caused by absorption of atmospheric CO₂; harms organisms that build CaCO₃ structures.
Positive feedback (climate)
Examiner keyword
Process whereby warming triggers further warming (e.g. ice-albedo, permafrost methane).

Common Mistakes and Misconceptions — Climate Change

The traps other students keep falling into on climate change questions — taken from recent IB DP Biology SL examiner reports and mark schemes — and how to avoid them.

✕Calling all greenhouse gases 'pollution'.
Why it happens
Conflating natural and enhanced effects.
How to avoid it
Natural greenhouse effect is essential for life. The CONCERN is the ENHANCED effect from human emissions.
✕Confusing the greenhouse effect with the ozone hole.
Why it happens
Both are atmospheric issues.
How to avoid it
Greenhouse = infrared absorption → warming. Ozone hole = UV transmission → skin cancer. Different mechanisms.
✕Equating ocean acidification with acid rain.
Why it happens
Similar word.
How to avoid it
Acid rain = sulfuric/nitric acids from SO₂/NOₓ. Ocean acidification = CO₂ dissolution into seawater.

Climate Change — frequently asked questions

The things students keep getting wrong in this sub-topic, answered.

Climate Change

Short Notes - Climate Change

Detailed Study Notes

At a glance

What you’ll learn

Quick recap

Memorise this

How it’s examined

Take this whole topic with you

1How greenhouse gases warm the Earth

2Coral bleaching mechanism

3Ocean acidification harm

4Compare two mitigation strategies

Greenhouse effect

Ocean acidification

Positive feedback (climate)

✕Calling all greenhouse gases 'pollution'.

✕Confusing the greenhouse effect with the ozone hole.

✕Equating ocean acidification with acid rain.

Climate Change — frequently asked questions