What you'll learn
This revision guide covers the Climate Change component of Hazardous Earth in the Pearson Edexcel International IGCSE Geography specification. You'll explore evidence for climate change throughout Earth's history, investigate natural and human causes, examine global and regional impacts, and evaluate management strategies. This topic requires you to analyse data, understand feedback mechanisms, and assess different responses to climate change.
Key terms and definitions
Greenhouse effect — the natural process by which certain gases in the atmosphere trap heat from the Sun, keeping Earth warm enough to support life
Enhanced greenhouse effect — the strengthening of the greenhouse effect due to human activities releasing additional greenhouse gases, causing global temperatures to rise
Mitigation — actions taken to reduce or prevent greenhouse gas emissions, thereby limiting the extent of future climate change
Adaptation — adjustments made to natural or human systems in response to actual or expected climate change, reducing vulnerability to its impacts
Feedback mechanisms — processes that either amplify (positive feedback) or reduce (negative feedback) the effects of climate change
Quaternary period — the most recent geological period, spanning the last 2.6 million years, characterised by repeated glacial and interglacial cycles
Carbon footprint — the total amount of greenhouse gases produced directly and indirectly by an individual, organisation, event or product
Climate forcings — factors that influence Earth's energy balance and cause temperature changes, including solar output, volcanic eruptions and greenhouse gas concentrations
Core concepts
Evidence for climate change
Climate change operates across different timescales, from millions of years to decades. Understanding past climate helps scientists predict future trends.
Long-term evidence (pre-industrial):
- Ice cores from Antarctica and Greenland contain trapped air bubbles preserving atmospheric composition from up to 800,000 years ago
- Tree rings show annual growth patterns influenced by temperature and rainfall; wider rings indicate warmer, wetter conditions
- Historical records including paintings, diaries and harvest dates provide evidence from the Medieval Warm Period (900-1300 CE) and Little Ice Age (1300-1850 CE)
- Pollen analysis reveals which plant species dominated different periods, indicating temperature and moisture conditions
- Sea level changes shown through raised beaches and submerged forests demonstrate past warming and cooling
Recent evidence (since industrialisation):
- Global temperature records show a 1.1°C increase since 1880, with accelerated warming since 1980
- Satellite data reveals Arctic sea ice has declined by approximately 13% per decade since 1979
- Glacier retreat documented worldwide, including Mount Kilimanjaro losing 85% of its ice cap since 1912
- Sea level rise of approximately 20cm since 1900, measured by tide gauges and satellite altimetry
- Ocean temperature measurements show warming in the upper 700m of oceans globally
Natural causes of climate change
Several natural factors have driven climate change throughout Earth's history, operating on different timescales.
Orbital changes (Milankovitch cycles):
- Eccentricity — Earth's orbit varies from nearly circular to more elliptical over 100,000 years, affecting distance from the Sun
- Axial tilt — the angle of Earth's axis varies between 22.1° and 24.5° over 41,000 years, influencing seasonal contrast
- Precession — Earth's axis wobbles like a spinning top over 26,000 years, changing which hemisphere receives more solar radiation during summer
- These cycles explain glacial-interglacial patterns during the Quaternary period
Volcanic activity:
- Large eruptions eject ash and sulfur dioxide into the stratosphere, forming aerosols that reflect solar radiation
- Short-term cooling effect lasting 2-3 years, as seen after Mount Pinatubo (1991) which reduced global temperatures by 0.5°C
- Major eruptions like Tambora (1815) caused the "Year Without a Summer" in 1816
Solar output:
- Sunspot activity follows an 11-year cycle, with variations in solar radiation of approximately 0.1%
- Prolonged periods of low sunspot activity (Maunder Minimum, 1645-1715) coincided with the Little Ice Age
- Limited impact on recent warming trends compared to greenhouse gas increases
Human causes of climate change
Human activities since the Industrial Revolution have dramatically increased atmospheric greenhouse gas concentrations, enhancing the natural greenhouse effect.
Fossil fuel combustion:
- Coal, oil and natural gas burning for electricity, transport and industry releases carbon dioxide
- Atmospheric CO₂ has increased from 280ppm (pre-industrial) to over 420ppm today
- Accounts for approximately 75% of human-caused greenhouse gas emissions
- Power stations, vehicles and industrial processes are primary sources
Agriculture:
- Livestock farming produces methane through enteric fermentation (digestion in cattle)
- Rice paddies create anaerobic conditions releasing methane
- Deforestation for agricultural land reduces carbon storage and releases CO₂
- Fertiliser use releases nitrous oxide, a greenhouse gas 300 times more potent than CO₂
Deforestation:
- Tropical rainforest clearance in Amazonia, Southeast Asia and Central Africa
- Removes trees that absorb CO₂ through photosynthesis
- Burning vegetation releases stored carbon
- Approximately 10 million hectares cleared annually
Industrial processes:
- Cement production releases CO₂ through chemical reactions and fuel combustion
- Refrigerants and air conditioning systems release hydrofluorocarbons (HFCs)
- Mining and waste disposal generate methane emissions
Impacts of climate change
Climate change produces varied impacts across different spatial scales, affecting physical environments and human systems.
Global impacts:
- Sea level rise threatens low-lying coastal areas and small island nations like the Maldives and Tuvalu
- Melting ice sheets in Greenland and Antarctica contribute to rising seas
- Ocean acidification as oceans absorb excess CO₂, affecting marine ecosystems and coral reefs
- Shifting climate zones alter global precipitation patterns and agricultural zones
- Species extinction and migration as habitats change faster than adaptation rates
Regional impacts — tropical areas:
- Increased intensity of tropical cyclones in the Caribbean, though not necessarily more frequent
- Coral bleaching events in the Great Barrier Reef and Caribbean when ocean temperatures exceed 1-2°C above normal
- Changing rainfall patterns affect monsoons in South Asia, impacting agriculture
- Drought in sub-Saharan Africa reduces food security in countries like Somalia and Ethiopia
Regional impacts — polar and high-latitude areas:
- Arctic warming at twice the global average rate (Arctic amplification)
- Permafrost thaw releases methane and destabilises infrastructure in Alaska, Canada and Siberia
- Loss of sea ice affects polar bear hunting grounds and indigenous communities
- Opening of Northwest Passage creates new shipping routes
Regional impacts — mid-latitudes:
- More frequent and intense heatwaves, as seen in Europe (2003, 2019) and the UK (2022)
- Changing precipitation patterns increase flood risk in some areas, drought in others
- Earlier spring arrival affects agriculture and ecosystems
- Winter warming reduces snow cover and affects ski tourism
Positive feedback mechanisms:
- Ice-albedo feedback: melting ice exposes darker land/ocean surfaces, which absorb more heat, causing further melting
- Permafrost thaw releases methane and CO₂, enhancing warming
- Forest dieback releases stored carbon, contributing to atmospheric CO₂
Mitigation strategies
Mitigation aims to reduce greenhouse gas emissions and enhance carbon sinks to limit future warming.
Renewable energy:
- Wind farms (offshore UK sites generate significant electricity)
- Solar photovoltaic panels increasingly cost-competitive
- Hydroelectric power in countries like Norway provides 95% of electricity
- Reduces reliance on fossil fuels
Carbon capture and storage (CCS):
- Technology captures CO₂ from power stations and industrial sources
- Stored underground in geological formations
- Drax power station (UK) testing BECCS (bioenergy with CCS)
- Expensive and not yet widely implemented
Afforestation and reforestation:
- Planting trees absorbs CO₂ from atmosphere
- Bonn Challenge aims to restore 350 million hectares globally by 2030
- Protects biodiversity and provides ecosystem services
- Requires land and long-term management
International agreements:
- Paris Agreement (2015) — 195 countries committed to limiting warming to well below 2°C, ideally 1.5°C
- Nationally Determined Contributions (NDCs) outline each country's emission reduction targets
- UK legally committed to net zero emissions by 2050
- Challenges include enforcement and varying national commitments
Alternative transport:
- Electric vehicles reduce transport emissions when powered by renewable electricity
- Public transport investment reduces individual car use
- Cycling infrastructure in cities like Copenhagen
- Aviation remains difficult to decarbonise
Adaptation strategies
Adaptation helps communities cope with unavoidable climate change impacts.
Water management:
- Water storage and reservoir expansion in drought-prone areas
- Desalination plants in arid regions like Middle East
- Improved irrigation efficiency in agriculture
- Flood defences like Thames Barrier (London) upgraded for higher sea levels
Agricultural adaptations:
- Drought-resistant crop varieties developed for changing conditions
- Changing planting dates to match altered growing seasons
- Crop diversification reduces risk from climate variability
- Irrigation system improvements in regions like California
Land use planning:
- Restricting development in flood-risk zones
- Managed retreat allowing coastal areas to flood naturally
- Building codes requiring climate-resilient construction
- Green infrastructure in cities to manage flooding and heat
Emergency preparation:
- Early warning systems for extreme weather events
- Evacuation plans for vulnerable coastal communities
- Healthcare preparations for heat-related illness
- Insurance schemes to spread climate risk
Challenges of adaptation:
- High costs, particularly for low-income countries
- Benefits may take years to materialise
- Requires accurate climate projections
- May create new problems (e.g., desalination impacts on marine ecosystems)
Worked examples
Example 1: Explain how ice core data provides evidence for past climate change. (4 marks)
Answer: Ice cores are cylinders drilled from ice sheets in Antarctica and Greenland (1). They contain layers of ice formed from annual snowfall over hundreds of thousands of years (1). Trapped air bubbles preserve atmospheric gases including CO₂ and methane from when the ice formed (1). Scientists analyse these bubbles to determine past greenhouse gas concentrations and temperatures, revealing that CO₂ levels and temperatures are closely correlated throughout history (1).
Examiner note: This answer gains full marks by identifying the source, explaining the formation process, describing what is measured, and linking to climate conclusions. Each developmental point scores one mark.
Example 2: Assess the effectiveness of mitigation strategies in tackling climate change. (8 marks)
Answer: Mitigation strategies aim to reduce greenhouse gas emissions and limit future warming. Renewable energy has proven effective in some countries; Norway generates 95% of electricity from hydropower, dramatically reducing emissions from this sector. However, intermittency of wind and solar requires backup systems or storage, limiting effectiveness. The UK has successfully reduced coal use through offshore wind farms, demonstrating that mitigation can work with sufficient investment.
International agreements like the Paris Agreement show potential effectiveness as 195 countries committed to emission reductions. However, effectiveness is limited by voluntary nature of targets and insufficient action from major emitters like China and the USA. The agreement lacks enforcement mechanisms, reducing its effectiveness.
Carbon capture and storage could theoretically remove emissions from fossil fuel use, allowing continued energy generation while reducing atmospheric CO₂. However, CCS remains expensive and unproven at scale, with only a few operational facilities worldwide like Drax in the UK testing the technology. Its effectiveness is therefore currently limited.
Overall, mitigation strategies show variable effectiveness. Renewable energy and afforestation have demonstrated measurable emission reductions where implemented comprehensively. However, global effectiveness is limited by costs, political will, and the scale of change required. Meeting Paris Agreement targets requires much faster implementation than currently occurring.
Examiner note: This answer reaches Level 3 (7-8 marks) by providing detailed, place-specific examples, evaluating different strategies, and reaching a balanced conclusion. It demonstrates chains of reasoning and uses evidence to support judgements about effectiveness.
Example 3: Explain one positive feedback mechanism associated with climate change. (3 marks)
Answer: The ice-albedo feedback mechanism occurs when rising temperatures melt Arctic sea ice (1). This exposes darker ocean water which has lower albedo (reflectivity) than white ice (1). The darker surface absorbs more solar radiation, causing further warming and additional ice melt, amplifying the original temperature increase (1).
Examiner note: Full marks awarded for naming the mechanism, explaining the process, and describing the amplifying effect. Use of technical terminology (albedo) strengthens the answer.
Common mistakes and how to avoid them
Confusing weather and climate — Climate refers to average conditions over 30+ years; weather describes short-term atmospheric conditions. Always use "climate change" not "weather change" in your answers.
Vague case study details — Avoid writing "some countries" or "many areas." Use specific named locations: "the Maldives faces sea level rise threatening 80% of land below 1m elevation" rather than "island nations are threatened."
Mixing up mitigation and adaptation — Mitigation reduces greenhouse gas emissions (e.g., renewable energy); adaptation helps cope with impacts (e.g., flood defences). Check which the question asks for.
Failing to explain feedback mechanisms fully — Don't just state that feedback exists; explain the process step-by-step showing how the initial change is amplified (positive) or reduced (negative).
Ignoring command words — "Describe" requires you to say what happens; "explain" needs you to say why/how it happens; "assess" demands evaluation of effectiveness or importance with a conclusion.
Not using data when provided — If graphs, tables or maps are given in the question, you must reference specific values or patterns from them to access higher mark bands.
Exam technique for "Hazardous Earth: Climate Change"
Command word precision: "Suggest" allows reasonable possibilities without specific case study knowledge; "Explain" always requires reasons/causes, not just description; "Assess" and "Evaluate" need you to weigh up positives/negatives and reach a judgement, typically in 8-9 mark questions.
Case study specificity: Learn precise statistics and named locations for at least one example of impacts (e.g., Maldives for sea level rise) and one mitigation/adaptation scheme (e.g., Thames Barrier). Names, dates and figures distinguish Level 3 answers from Level 2.
Link causes to consequences: Don't list impacts in isolation. Show chains of reasoning: "Deforestation in Amazonia releases CO₂ from burning vegetation AND removes trees that previously absorbed CO₂ through photosynthesis, therefore contributing to enhanced greenhouse effect."
Extended prose questions: In 8-9 mark questions, write in paragraphs, not bullet points. Include an introduction stating your overall argument, develop 2-3 main points with evidence, and conclude by directly answering the question posed.
Quick revision summary
Climate change shows clear evidence from ice cores, temperature records and retreating glaciers. Natural causes include Milankovitch cycles, volcanic eruptions and solar variation, but human activities — particularly fossil fuel combustion, deforestation and agriculture — have enhanced the greenhouse effect since industrialisation. Impacts vary globally from sea level rise threatening the Maldives to Arctic amplification affecting permafrost. Positive feedbacks like ice-albedo amplify warming. Mitigation strategies (renewable energy, Paris Agreement, afforestation) aim to reduce emissions while adaptation (flood defences, drought-resistant crops) helps communities cope with unavoidable changes.