Climate change—causes and impacts
· Climate = typical atmospheric conditions over time, mainly seasonal temperature and precipitation patterns.
· Weather = short-term atmospheric conditions; climate change = long-term shifts in climate patterns.
· Exam focus: explain anthropogenic causes, interpret evidence, analyse impacts, model feedback loops, and discuss perspectives / climate justice.
Anthropogenic causes of climate change
· Anthropogenic carbon dioxide emissions have caused atmospheric CO₂ concentrations to rise significantly.
· The rise began with the Industrial Revolution in late 18th-century Europe and accelerated especially after 1950 due to industrialization, population growth, and higher energy demand.
· Main human sources: burning fossil fuels, deforestation, industrial processes, agriculture, and land-use change.
· The enhanced greenhouse effect occurs when extra greenhouse gases (GHGs) trap more outgoing long-wave infrared radiation, increasing mean global temperature.
· Key anthropogenic GHGs: carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), plus smaller quantities of other GHGs.
· Global warming = increase in mean global temperature; climate change = broader changes, including precipitation, sea level, ocean circulation, extreme events, and biome shifts.
This diagram shows the basic mechanism of the greenhouse effect: short-wave solar radiation enters the atmosphere, while some outgoing long-wave heat radiation is absorbed by greenhouse gases. It is useful for explaining why increased GHG concentrations enhance global warming. Source
Evidence for climate change
· Ice cores, tree rings, and deposited sediments provide proxy data about past climates.
· These records show a positive correlation between atmospheric CO₂ concentration and global temperature over glacial–interglacial cycles.
· Students should be able to interpret graphs over the last 800,000 years, comparing CO₂ concentration and temperature change.
· Direct measurements from weather stations, observatories, radar, and satellites provide modern evidence for climate and land-use change.
· Evidence from long-term graphs includes rising atmospheric CO₂, increasing oceanic CO₂, and links to ocean acidification.
· Exam phrase: correlation does not prove causation alone, but multiple independent datasets support anthropogenic global warming.
Enhanced greenhouse effect and GHGs
· Natural greenhouse effect is essential because it keeps Earth warm enough for life.
· Human activity has enhanced this effect by increasing GHG concentrations.
· CO₂: mainly from fossil fuel combustion, cement production, and deforestation.
· CH₄: from ruminant livestock, rice paddies, landfills, wetlands, and anaerobic decomposition; it is a potent GHG.
· N₂O: linked to synthetic fertilizers, agriculture, and disruption of the nitrogen cycle.
· Water vapour is a major GHG but is usually treated as a feedback, not a direct mitigation target, because its atmospheric concentration changes with temperature.
· High-scoring answers distinguish natural greenhouse effect from enhanced greenhouse effect.
Impacts on ecosystems
· Climate change affects ecosystems from local to global scales.
· Impacts reduce ecosystem resilience, especially where biodiversity is already low or other stressors are present.
· Biome shifts: warming drives many biomes poleward and to higher altitude.
· Local impacts include coral bleaching, desertification, changes in species distributions, altered phenology, and disrupted food webs.
· Global impacts include sea-level rise, changes to ocean circulation, ocean warming, and ocean acidification.
· Some regions may experience increased natural productivity, but this depends on water availability, nutrients, soil, species tolerance, and disturbance frequency.
· Strong exam answers use a named real-world example, such as coral bleaching on the Great Barrier Reef or desertification in the Sahel.
Impacts on human societies
· Climate change affects societies at different scales and under different socio-economic conditions.
· Key impacts include changes to health, water supply, agriculture, food security, infrastructure, housing, and migration.
· Water supply may be affected by drought, altered precipitation, glacier retreat, saltwater intrusion, and damaged infrastructure.
· Agriculture may be affected by heat stress, drought, flooding, pests, soil degradation, and shifting growing seasons.
· Health impacts include heat-related illness, spread of vector-borne disease, food insecurity, and impacts from extreme weather.
· Infrastructure is vulnerable to flooding, storms, sea-level rise, permafrost thaw, and heat damage.
· Social resilience depends on wealth, governance, technology, healthcare, infrastructure quality, education, and disaster preparedness.
· High-scoring answers compare impacts on high-income and low-income societies and link this to climate justice.
Feedback loops and system models
· Systems diagrams can represent climate-change causes, effects, feedback loops, and changes to the global energy balance.
· Positive feedback amplifies change and can move systems away from equilibrium.
· Example: ice–albedo feedback → warming melts ice → lower albedo → more solar radiation absorbed → more warming.
· Example: methane release feedback → warming thaws permafrost / methane stores → more CH₄ released → more warming.
· Negative feedback counteracts change and stabilizes systems, but may be weaker or slower than positive feedbacks.
· Climate models should include solar radiation variation, terrestrial albedo changes, methane release, and associated feedbacks.
· Exam skill: draw arrows clearly, label storages, flows, and whether each feedback is positive or negative.
This block diagram shows how climate feedbacks can amplify or reduce warming. It is especially useful for revising feedback loops, albedo change, water vapour, cloud effects, and other interactions in climate systems. Source
Planetary boundary for climate change
· Evidence suggests Earth has already passed the planetary boundary for climate change.
· The planetary boundaries model identifies limits of human disturbance that, if crossed, increase the risk of abrupt and irreversible Earth-system change.
· For climate change, relevant indicators include atmospheric CO₂, radiative forcing, global temperature rise, and Earth-system feedbacks.
· Crossing the climate boundary increases risk of tipping points, loss of resilience, and movement toward a different Earth-system equilibrium.
· In essays, link this to systems thinking, feedback loops, and precautionary principle.
Perspectives and responses to climate change
· Perspectives on climate change vary between individuals and societies.
· Influences include values, worldviews, scientific understanding, economic conditions, politics, media, religion, laws, local events, and lived experience.
· Technocentric perspectives may emphasize technological solutions, innovation, geoengineering, and economic growth.
· Anthropocentric perspectives may focus on human welfare, development, jobs, energy security, and social stability.
· Ecocentric perspectives may prioritize ecosystem integrity, biodiversity, reduced consumption, and intrinsic value of nature.
· High-scoring answers explain why perspectives affect urgency, policy support, behaviour change, and willingness to accept costs.
· Include personal perspectives where relevant, but keep exam answers evidence-based.
HL only: climate data, models, scenarios and hindcasting
· Direct measurements include long-term records from weather stations, observatories, radar, and satellites.
· Indirect proxy measurements include isotope measurements from ice cores, dendrochronology from tree rings, and pollen from peat cores.
· Both direct and indirect measurements help create climate models.
· Global climate models manipulate climate-system inputs to predict outputs using equations representing Earth-system processes and interactions.
· Models have uncertainty because inputs, including proxy data, can be uncertain; outputs therefore produce a range of possible future outcomes.
· Hindcasting tests model validity by running a model backwards from the present and comparing results with known past climate data.
· Climate models use different scenarios to predict possible impacts, such as sea-level rise, local temperature, and precipitation patterns.
· Strong HL answers evaluate models using both usefulness and limitations.
HL only: thresholds, tipping points and tipping cascades
· Climate models show Earth may approach a critical threshold, causing a shift to a new equilibrium.
· Tipping points may be rapid, unexpected, and potentially catastrophic.
· Examples include melting Antarctic ice sheets, slowing of Atlantic thermohaline circulation, and Amazon Rainforest–Cerrado transition (CAT).
· Local systems also have thresholds, such as coral reefs shifting to algae-dominated systems after repeated bleaching.
· Tipping cascades occur when two or more tipping points interact, increasing uncertainty about the scale and pace of climate change.
· Tipping points may be biotic, abiotic, or a combination of both.
· Exam phrase: tipping cascades make predictions difficult because Earth systems are interconnected and feedbacks may amplify each other.
This diagram links causes, effects, and feedbacks in a simplified climate-change system. It is useful for practising ESS systems thinking because it shows how human actions can trigger environmental impacts and reinforcing feedback pathways. Source
HL only: climate justice, responsibility and vulnerability
· Countries differ in their responsibility for climate change and their vulnerability to its impacts.
· Responsibility can be compared using current emissions, cumulative emissions since the Industrial Revolution, emissions per person, and emissions per country.
· The least responsible countries and groups are often among the most vulnerable, creating issues of equity and climate justice.
· Vulnerability is increased by poverty, weak infrastructure, low adaptive capacity, dependence on climate-sensitive agriculture, coastal exposure, and limited political power.
· Political and economic implications include disputes over finance, loss and damage, historical responsibility, fossil-fuel dependence, and development rights.
· High-scoring HL answers compare at least two contrasting countries or groups and use terms such as equity, justice, resilience, responsibility, and adaptive capacity.
Checklist: can you do this?
· Explain how anthropogenic GHG emissions enhance the greenhouse effect and cause global warming.
· Interpret long-term graphs showing CO₂ concentration, temperature, and evidence from ice cores / tree rings / sediments.
· Draw and explain positive feedback loops, including ice–albedo and methane release.
· Analyse impacts on both ecosystems and human societies, using at least one named real-world example.
· For HL, evaluate climate models, hindcasting, tipping points, tipping cascades, and climate justice.
Common exam traps
· Do not say climate and weather are the same.
· Do not say the greenhouse effect is bad; the natural greenhouse effect is essential, but the enhanced greenhouse effect drives current warming.
· Do not rely only on vague impacts such as “animals die”; explain mechanisms like habitat shift, reduced resilience, food-web disruption, or coral bleaching.
· Do not confuse global warming with all of climate change.
· Do not describe feedback loops without stating whether they are positive or negative and how they affect equilibrium.
· Do not ignore scale: climate change impacts are local, regional, national, and global.
· For HL, do not treat model predictions as exact; discuss scenarios, uncertainty, and hindcasting.
Shubhi is a seasoned educational specialist with a sharp focus on IB, A-level, GCSE, AP, and MCAT sciences. With 6+ years of expertise, she excels in advanced curriculum guidance and creating precise educational resources, ensuring expert instruction and deep student comprehension of complex science concepts.
Shubhi is a seasoned educational specialist with a sharp focus on IB, A-level, GCSE, AP, and MCAT sciences. With 6+ years of expertise, she excels in advanced curriculum guidance and creating precise educational resources, ensuring expert instruction and deep student comprehension of complex science concepts.