What you'll learn
This revision guide covers everything you need to know about Changing Climate for OCR GCSE Geography. You'll explore evidence for climate change throughout Earth's history, understand natural and human causes of climate shifts, and examine the global and local impacts of current warming trends. The guide also addresses mitigation and adaptation strategies that governments and communities are implementing worldwide.
Key terms and definitions
Climate change — long-term shifts in global or regional temperature and weather patterns, particularly the warming trend since the mid-20th century caused primarily by human activities.
Greenhouse effect — the natural process where greenhouse gases in Earth's atmosphere trap heat from the sun, keeping the planet 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 the emission of greenhouse gases to limit the magnitude of future climate change.
Adaptation — adjustments made to natural or human systems in response to actual or expected climate change, which moderates harm or exploits beneficial opportunities.
Carbon footprint — the total amount of greenhouse gases (particularly carbon dioxide) produced directly and indirectly by human activities, measured in equivalent tonnes of CO₂.
Quaternary period — the most recent geological time period, spanning the last 2.6 million years, characterized by cyclical ice ages and warmer interglacial periods.
Feedback loop — a cycle where the output of a system either amplifies (positive feedback) or dampens (negative feedback) the original change.
Core concepts
Evidence for climate change
Climate scientists use multiple sources of evidence to reconstruct past climates and monitor current changes:
Historical records
- Temperature measurements from weather stations (dating back to 1850s)
- Ship and satellite data for ocean temperatures
- Rainfall records and phenological data (timing of seasonal events like flower blooming)
Natural archives
- 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 reflecting temperature and rainfall variations
- Pollen analysis in peat bogs reveals which plant species thrived in past climates
- Ocean sediment cores contain remains of organisms sensitive to temperature changes
Recent observational evidence
- Global average temperature has increased by approximately 1.1°C since pre-industrial times
- Arctic sea ice extent has declined by 13% per decade since 1979
- Sea levels have risen by 20cm since 1900
- Glaciers worldwide are retreating at accelerating rates
Natural causes of climate change
Climate has fluctuated throughout Earth's history due to natural factors:
Orbital changes (Milankovitch cycles) These occur over tens of thousands of years and include:
- Eccentricity: Earth's orbit changes from circular to elliptical over 100,000 years
- Axial tilt: The angle of Earth's axis varies between 22.1° and 24.5° over 41,000 years
- Precession: Earth's axis wobbles like a spinning top over 26,000 years
These changes alter the amount and distribution of solar radiation reaching Earth, triggering ice ages and interglacial periods.
Volcanic activity
- Major eruptions eject ash and sulfur dioxide into the stratosphere
- Particles reflect solar radiation back to space, causing short-term cooling
- Mount Pinatubo (1991) reduced global temperatures by 0.5°C for two years
- Large-scale volcanic activity can trigger longer cooling periods
Solar output variations
- The sun's energy output fluctuates in 11-year cycles (sunspot activity)
- Longer-term variations occur over centuries
- Changes are relatively small but can influence climate, particularly during the Little Ice Age (1300-1850)
Human causes of climate change
Human activities since the Industrial Revolution have dramatically increased greenhouse gas concentrations:
Fossil fuel combustion
- Burning coal, oil and natural gas for energy releases CO₂
- Power stations, vehicles, and industrial processes are primary sources
- Atmospheric CO₂ has increased from 280ppm (pre-industrial) to over 420ppm today
- Responsible for approximately 75% of human greenhouse gas emissions
Agriculture
- Livestock farming produces methane through enteric fermentation (cattle digestion)
- Rice paddies generate methane in waterlogged, anaerobic conditions
- Fertilizer application releases nitrous oxide
- Agriculture contributes approximately 18% of global greenhouse gas emissions
Deforestation
- Removal of tropical rainforests, particularly in the Amazon, Indonesia and the Congo Basin
- Trees absorb CO₂ during photosynthesis; their removal reduces this carbon sink
- Burning or decomposition of felled trees releases stored carbon
- Deforestation accounts for roughly 10% of annual CO₂ emissions
Industrial processes
- Cement production releases CO₂ when limestone is heated
- Chemical manufacturing emits various greenhouse gases
- Waste decomposition in landfills produces methane
Impacts of climate change
Climate change affects physical environments and human systems globally:
Environmental impacts
Rising temperatures:
- Thermal expansion of oceans contributes to sea level rise
- Melting ice sheets and glaciers add water to oceans
- Permafrost thawing in Arctic regions releases stored methane
- Species ranges shift poleward and to higher altitudes
Extreme weather:
- Increased frequency and intensity of heatwaves
- More severe tropical storms due to warmer ocean temperatures
- Changes to precipitation patterns causing droughts in some regions, flooding in others
- The UK experiences more intense winter storms and increased flood risk
Impacts on ecosystems
- Coral bleaching when ocean temperatures rise above 1-2°C above normal
- The Great Barrier Reef experienced severe bleaching events in 2016, 2017 and 2020
- Arctic species like polar bears face habitat loss as sea ice diminishes
- Changes to migration patterns and breeding seasons disrupt food chains
Economic impacts
Developing countries:
- Bangladesh faces increased coastal flooding, threatening 15 million people in low-lying areas
- Small Island Developing States like the Maldives risk complete submersion
- Reduced agricultural productivity in sub-Saharan Africa due to drought
- Tropical diseases like malaria expand into new regions
Developed countries:
- UK agriculture faces challenges from changed growing seasons and increased pests
- Insurance costs rise due to more frequent extreme weather events
- Coastal infrastructure requires expensive defenses (Thames Barrier upgrades)
- However, some regions may benefit from longer growing seasons and reduced heating costs
Mitigation strategies
Mitigation aims to reduce greenhouse gas emissions:
Alternative energy production
- Wind power: UK has largest offshore wind capacity in Europe (13GW installed)
- Solar energy: costs decreased 90% since 2010, making it economically viable
- Hydroelectric power: established technology but limited suitable sites in UK
- Nuclear power: low-carbon but concerns about waste and costs (Hinkley Point C)
- Tidal and wave energy: UK exploring potential in Severn Estuary
Carbon capture and storage (CCS)
- Technology captures CO₂ from power stations before release
- CO₂ is transported and stored in underground geological formations
- Drax power station in Yorkshire testing bioenergy with CCS (BECCS)
- Technology remains expensive and unproven at large scale
Afforestation and reforestation
- Planting trees creates carbon sinks absorbing CO₂
- UK government committed to planting 30,000 hectares of trees annually by 2025
- REDD+ schemes pay developing countries to protect existing forests
- Trees provide co-benefits: biodiversity, flood management, recreation
International agreements
- Paris Agreement (2015): limit warming to well below 2°C, preferably 1.5°C
- Countries submit Nationally Determined Contributions (NDCs) outlining emission reduction targets
- UK legally committed to net zero emissions by 2050 (Climate Change Act)
- COP26 in Glasgow (2021) strengthened commitments but implementation gaps remain
Individual actions
- Reducing energy consumption in homes (insulation, efficient appliances)
- Transport choices: cycling, public transport, electric vehicles
- Dietary changes: reducing meat and dairy consumption
- Supporting renewable energy suppliers
Adaptation strategies
Adaptation involves adjusting to current and future climate impacts:
Water management
- Water transfer schemes move water from surplus to deficit areas
- Desalination plants in water-scarce countries (Middle East, California)
- Rainwater harvesting and greywater recycling reduce demand
- UK water companies reducing leakage (currently loses 3 billion litres daily)
Agricultural adjustments
- Drought-resistant crop varieties developed through selective breeding and genetic modification
- Changed planting dates to match shifting seasons
- Crop diversification reduces vulnerability to single climate threat
- Precision agriculture uses technology to optimize water and fertilizer use
Flood defenses
- Hard engineering: Thames Barrier protects London from storm surges (since 1982)
- Soft engineering: managed realignment creates salt marshes absorbing wave energy
- Sustainable urban drainage systems (SUDS): permeable surfaces reduce runoff
- Netherlands investing €20 billion in Delta Programme strengthening coastal defenses
Planning and building design
- Building codes requiring climate resilience in new developments
- Cool roofs and green roofs reduce urban heat island effect
- Flood-resistant materials and raised foundations in vulnerable areas
- Climate-proofing infrastructure: railways, roads, water treatment plants
Worked examples
Example 1: Explain how ice cores provide evidence for climate change (4 marks)
Model answer: Ice cores are cylindrical samples drilled from ice sheets in Antarctica and Greenland (1). They contain layers of ice formed from annual snowfall, with the deepest layers being the oldest (1). Air bubbles trapped in the ice preserve the atmospheric composition from when the snow fell, allowing scientists to measure past CO₂ levels (1). Analysis shows CO₂ concentrations correlate closely with temperature changes over the past 800,000 years, demonstrating the link between greenhouse gases and global temperature (1).
Examiner note: This answer gains full marks by explaining the process (how cores are formed), the method (measuring trapped air), and the significance (correlation with temperature). Each distinct point earns one mark.
Example 2: Assess the effectiveness of mitigation strategies in reducing climate change (9 marks + 3 SPaG)
Model answer structure:
Introduction: Mitigation strategies aim to reduce greenhouse gas emissions through various approaches including renewable energy, carbon capture, and international cooperation.
Paragraph 1 - Renewable energy: Renewable energy effectively reduces emissions by replacing fossil fuels. The UK's offshore wind capacity has expanded significantly, now generating 13GW. This has contributed to a 44% reduction in UK emissions since 1990. Solar power costs have fallen 90%, making it economically competitive. However, intermittency requires backup systems, and manufacturing solar panels creates emissions.
Paragraph 2 - International agreements: The Paris Agreement established global targets, with 195 countries committing to limit warming to well below 2°C. This demonstrates international cooperation and political will. The UK's legally binding net zero target by 2050 drives policy changes. However, many countries are not meeting their commitments, and enforcement mechanisms are weak. Developing countries argue they need support to transition away from fossil fuels.
Paragraph 3 - Individual limitations: While individual actions like reducing meat consumption or using public transport help reduce carbon footprints, their impact is limited without systemic change. Wealthy countries have greater capacity to implement expensive technologies like CCS compared to developing nations. The time lag means even with immediate action, warming will continue for decades due to past emissions.
Conclusion: Mitigation strategies are necessary and show some effectiveness, particularly renewable energy deployment. However, current efforts are insufficient to meet Paris Agreement targets, requiring more ambitious policies and international cooperation to be truly effective.
Examiner note: Level 3 answer (7-9 marks) requires detailed knowledge, clear assessment of effectiveness, and a balanced conclusion. SPaG marks awarded for accurate spelling, punctuation and grammar throughout.
Example 3: Suggest how Bangladesh can adapt to climate change impacts (6 marks)
Model answer: Bangladesh faces severe flooding from sea level rise and increased monsoon intensity, threatening 15 million people in coastal areas. The country could implement early warning systems using satellite data to predict floods, allowing evacuation (2 marks - specific strategy with explanation). Building elevated homes on stilts would protect people and possessions from floodwaters, as demonstrated in successful projects in southern regions (2 marks - detailed adaptation with example). Growing flood-resistant rice varieties like BRRI dhan 51/52 would maintain food security during waterlogging, supporting subsistence farmers (2 marks - agricultural adaptation linked to local context).
Examiner note: Each suggestion needs development and context to earn full marks. Simply listing adaptations without explanation earns minimal credit.
Common mistakes and how to avoid them
Confusing weather and climate: Weather refers to short-term atmospheric conditions (days/weeks), while climate describes long-term patterns (30+ years). Always specify you're discussing climate when answering questions about climate change.
Mixing up mitigation and adaptation: Mitigation reduces causes (greenhouse gas emissions), while adaptation manages consequences (impacts already occurring). Remember: mitigation = prevention, adaptation = response.
Stating correlation proves causation: Ice core data shows CO₂ and temperature correlate, but you must explain the mechanism (greenhouse effect) to demonstrate causation. Examiners want understanding, not just pattern description.
Ignoring timescales: Natural causes like Milankovitch cycles operate over tens of thousands of years and cannot explain the rapid warming of the past 150 years. Always match causes to appropriate timescales.
Providing vague examples: "Climate change affects countries" is too general. Use specific named examples: "Bangladesh faces coastal flooding affecting 15 million people" demonstrates detailed knowledge worth higher marks.
Overlooking negative impacts of solutions: Good evaluation acknowledges limitations. Renewable energy may reduce emissions but manufacturing has environmental costs; CCS is expensive and unproven at scale. Balanced answers earn higher marks.
Exam technique for "Changing Climate"
Command words matter: "Explain" requires causes/reasons (use "because," "this leads to"); "Assess" or "Evaluate" needs judgments about effectiveness/success with evidence; "Suggest" wants plausible ideas you can justify even without prior knowledge.
Use case studies effectively: Named examples demonstrate detailed knowledge. State the location, specific facts/figures, and link clearly to the question. Generic descriptions earn fewer marks than precise case study detail.
Structure longer answers: For 6+ mark questions, use paragraphs with clear topic sentences. Introduction stating what you'll cover, developed paragraphs with evidence, and conclusion summarizing your argument maximizes marks.
Watch mark allocations: 1 mark = 1 developed point (or 2 simple points). A 4-mark question needs four distinct ideas or two well-explained points. Don't write excessively for low-mark questions but ensure sufficient detail for high-mark ones.
Quick revision summary
Climate change involves long-term shifts in temperature and weather patterns. Evidence includes ice cores, tree rings, and modern measurements showing 1.1°C warming since pre-industrial times. Natural causes (orbital changes, volcanic activity, solar output) explain historical fluctuations, but current rapid warming results from human activities: fossil fuel combustion, deforestation, and agriculture increasing greenhouse gases. Impacts include rising sea levels, extreme weather, ecosystem disruption, and economic costs, affecting developing countries most severely. Mitigation strategies (renewable energy, international agreements, carbon capture) aim to reduce emissions, while adaptation strategies (flood defenses, drought-resistant crops, water management) help societies cope with unavoidable changes.