Theme 5 · Climate change
From evidence to action
Climate change describes long-term shifts in average weather patterns. Earth’s climate has changed naturally in the past, but the rapid warming observed since the industrial era is driven mainly by human activities that increase greenhouse-gas concentrations.
Learning objectives
What you should be able to do
5.1.1 · Evidence
How do we know the climate is changing?
Scientists combine direct measurements with natural climate archives. Agreement between independent sources makes the evidence much stronger.
Global temperature records
Thermometer, ship, buoy and satellite-based records show a strong long-term warming trend, despite short-term variation from year to year.
Explore the real data · NASA
NASA’s Global Temperature Earth Indicator includes the latest global temperature data, maps and explanations.
Ice cores and paleoclimate evidence
Ice cores trap bubbles of ancient atmosphere. Scientists analyse greenhouse gases, oxygen isotopes and dust to reconstruct climate conditions far beyond the instrumental record.
Explore ice-core data · NOAA NCEI
Access paleoclimate records and ice-core datasets from polar and mountain glaciers.
Sea ice and glaciers
Satellite observations show declining Arctic sea-ice extent and widespread glacier retreat. These observations provide visible evidence of a warming cryosphere.
Explore sea ice · NSIDC
The Sea Ice Index provides regularly updated Arctic and Antarctic sea-ice extent, concentration and anomaly data.
Historical records
Written accounts, harvest dates, paintings and other documentary evidence can help reconstruct regional climate before modern instruments, but these sources are most useful when compared with physical proxy data.
Explore paleoclimate methods · NASA
NASA Earth Observatory explains how ice, sediments, tree rings and other evidence reveal past climates.
5.1.2 · Natural causes
Why has Earth’s climate changed naturally?
Milankovitch cycles
Long-term changes in Earth’s orbit alter the seasonal and spatial distribution of incoming solar energy.
Eccentricity
Changes in the shape of Earth’s orbit over roughly 100,000 years.
Obliquity
Changes in axial tilt over roughly 41,000 years.
Precession
Changes in the direction of Earth’s axial wobble over roughly 19,000–23,000 years.
Solar activity
The Sun’s energy output varies slightly, including an approximately 11-year sunspot cycle. These variations can influence climate, but they do not explain the rapid recent warming trend.
Volcanic activity
Large explosive eruptions can inject sulphate aerosols into the stratosphere. These particles reflect incoming sunlight and can cause temporary global cooling.
Explore natural climate drivers · NASA
NASA explains how orbital changes, solar variability and volcanic activity influence climate, and why they cannot account for the current warming trend.
5.1.3 · Human causes
The enhanced greenhouse effect
The natural greenhouse effect keeps Earth warm enough for life. Human activities add greenhouse gases to the atmosphere, so more outgoing long-wave radiation is absorbed and re-radiated, increasing the amount of heat retained in the climate system.
Fossil fuels
Burning coal, oil and natural gas releases carbon dioxide from electricity generation, transport, heating and industry.
Deforestation
Forest loss reduces carbon uptake by photosynthesis and can release stored carbon through burning and decomposition.
Agriculture
Livestock and rice cultivation release methane, while fertilisers can release nitrous oxide. Agricultural expansion can also drive forest loss.
Explore the greenhouse effect · NASA
NASA explains the human causes of recent climate change and the role of greenhouse gases.
5.2 · Impacts
What changes as the planet warms?
Temperature and weather patterns
Average temperatures rise, heatwaves become more frequent and intense, and rainfall patterns change. Some regions face heavier rainfall, while others experience greater drought risk.
Explore future climate · IPCC
Compare temperature and precipitation changes at different warming levels in the IPCC Interactive Atlas.
Sea-level rise
Sea level rises because warmer seawater expands and because melting land ice adds water to the oceans. Coastal flooding, erosion, saltwater intrusion and storm-surge risk can all increase.
Explore ice-sheet change · NASA
NASA’s Earth Indicator tracks ice-sheet mass loss and its contribution to sea-level rise.
Food production
Heat, changing rainfall and drought can reduce yields, increase irrigation demand and alter where crops can be grown. Livestock and farm workers can also experience greater heat stress.
Ecosystems and health
Species ranges shift, coral reefs experience heat stress, and wildfire or disease risks can increase. Human health is affected by heat, air quality, food insecurity and changing disease patterns.
5.3 · Responses
Mitigation, adaptation and cooperation
Mitigation
Mitigation reduces the causes of climate change by lowering greenhouse-gas emissions or increasing carbon removal.
- renewable energy
- energy efficiency
- public and low-carbon transport
- reforestation
- lower-carbon production and consumption
Adaptation
Adaptation reduces vulnerability to present or expected climate impacts.
- flood protection and cyclone shelters
- heat-health plans
- drought-tolerant crops
- water conservation
- early-warning systems
Explore international climate action · UNFCCC
Read the official material on the Paris Agreement and Nationally Determined Contributions (NDCs).
5.3.3 · Specific example
Bangladesh: climate risk and response
Why is Bangladesh vulnerable?
Bangladesh lies in the low-lying Ganges–Brahmaputra–Meghna delta. Large populations are exposed to river flooding, tropical cyclones, storm surges, coastal erosion and salinity intrusion.
- flooding of homes and farmland
- salinisation of soils and freshwater
- crop and livelihood losses
- displacement and urban pressure
- greater coastal hazard exposure
How is Bangladesh responding?
- cyclone shelters and early-warning systems
- raised roads and embankments
- community evacuation planning
- salt-tolerant crops
- mangrove and ecosystem-based adaptation
Explore the case study · World Bank
See how Bangladesh is strengthening coastal resilience through shelters, polders and disaster-risk reduction.
Explore Bangladesh in 3D
Google Earth is best opened as an external 3D viewer rather than embedded directly. Use it to examine the delta, coastline, Sundarbans and the relationship between rivers and settlements.
Map exploration: Google Earth. Case-study source: World Bank coastal resilience programmes.
Exam practice
Check your understanding
Key terms
Language to use accurately
Explore like a Geographer
Go to the scientists, data and institutions
Use these trusted sources to investigate real observations, projections and climate responses beyond the lesson.
NASA Climate Evidence
Evidence, indicators and explanations of current climate change.
World Bank · Bangladesh
Coastal resilience and disaster-risk reduction in a highly exposed delta.
