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Welcome to GCSE A Q A Geography revision.

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Topic G 4: Climate change.

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Use your school’s selected case studies if they differ from these revision examples.

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Climate is the average pattern of weather over a long period, commonly 30 years.

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Climate change is a lasting change in those patterns, rather than a single unusual day.

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The Quaternary began about 2.6 million years ago.

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Its climate has alternated between colder glacial periods and warmer interglacial periods.

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We live in the Holocene interglacial, which began about 11,700 years ago.

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Ice cores contain trapped air bubbles that show past atmospheric gas concentrations.

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The ice's isotopes provide evidence about past temperatures; they are not direct thermometer readings.

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Pollen preserved in sediments shows which plants lived in an area, helping reconstruct earlier climates.

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Ocean sediments and other natural records also provide evidence beyond the instrumental record.

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Tree rings can show yearly changes in growth related to temperature or moisture.

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Their meaning depends on local conditions, so scientists compare multiple records rather than treating all narrow rings as cold years.

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Modern evidence includes instrumental temperature records, shrinking glaciers, loss of Arctic sea ice and rising sea level.

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Land ice melting adds water to the ocean; seawater also expands as it warms.

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Orbital changes alter the distribution of solar energy reaching Earth.

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Changes in orbit shape, axis tilt and wobble help explain glacial cycles over thousands of years.

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Variations in solar output can influence climate.

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They do not explain the rapid warming observed in recent decades; current warming is mainly driven by human greenhouse-gas emissions.

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Large explosive volcanic eruptions can send sulphur dioxide into the stratosphere.

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Reflective particles form and can cool Earth's surface temporarily.

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Volcanoes also emit carbon dioxide, but much less than present human activity.

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The natural greenhouse effect keeps Earth warmer than it would be without greenhouse gases.

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These gases absorb outgoing infrared radiation and emit radiation in all directions, including back towards the surface.

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The enhanced greenhouse effect.

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Greenhouse gases also emit radiation in all directions.

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Extra warming restores energy balance at a higher temperature.

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Burning coal, oil and gas releases carbon dioxide.

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More greenhouse gases strengthen the greenhouse effect, upsetting Earth's energy balance until the planet warms.

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Deforestation releases stored carbon when vegetation burns or decays and reduces the forest's future carbon uptake.

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Changes in land use can also affect water cycling and local temperatures.

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Agriculture releases methane from livestock and rice cultivation, and nitrous oxide from fertilised soils.

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Different gases have different warming effects and atmospheric lifetimes.

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Sea-level rise increases coastal flooding, erosion and saltwater intrusion.

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Low-lying islands, deltas and coastal settlements are particularly exposed.

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Changing rainfall and higher evaporation can worsen water shortages in some regions, while heavier rain raises flood risk elsewhere.

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Impacts vary between places and seasons.

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Heat can harm health and reduce crop yields, particularly where temperatures exceed a crop's tolerance.

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A longer growing season may help some cooler regions, but pests, water supply and heat extremes can offset benefits.

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Habitats shift as temperature and rainfall change.

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Species may move towards cooler areas or struggle to adapt; coral reefs are at risk from marine heatwaves and ocean warming.

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Melting land ice and thawing permafrost change landscapes and infrastructure.

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Thawing frozen soils can release greenhouse gases, reinforcing warming.

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Mitigation limits warming by reducing emissions or increasing carbon storage.

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Renewable energy, energy efficiency and lower-emission transport can reduce fossil-fuel use.

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Carbon capture can separate carbon dioxide from industrial emissions and store it underground.

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It has costs and energy requirements and needs secure long-term storage; it does not replace all other mitigation.

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Planting trees and restoring forests can remove carbon dioxide as trees grow.

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Protecting existing forests is also important, and carbon can be released again through fire or clearance.

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International agreements coordinate action across countries.

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The Paris Agreement aims to keep warming well below 2 degrees Celsius and pursue efforts to limit it to 1.5 degrees Celsius above pre-industrial levels;

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success depends on countries' actions.

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Adaptation reduces harm from changes that are happening or expected.

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Farmers may change crop varieties, sowing dates and irrigation methods to suit warmer or drier conditions.

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Water management includes reducing leakage, conserving supplies, collecting rainwater and using water more efficiently.

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New reservoirs or transfers have environmental and financial costs.

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Coastal adaptation includes sea defences, flood-resistant buildings and managed realignment.

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In some areas moving people or assets out of danger may be more sustainable than defending every location.

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Heat-health plans, shaded spaces and early warnings can reduce heatwave harm.

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Adaptation needs to account for people who are most exposed or least able to pay.

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Mitigation addresses the causes; adaptation addresses the impacts.

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A strong answer explains how a named action works and considers costs, limits or possible side effects.

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That completes Climate change.

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Revisit the notes and test yourself on the revision website.