12.4Chapter 12: The Carbon Cycle and Climate Change

Predicting the future — Alhussan Biology - Stage 9 Revision Notes & Topical Questions

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12.4 Predicting the future — Computer Climate Models — Alhussan International Academy — Biology (Stages 7–9) notes: Describe predicted impacts of future climate change and how computer climate models are built, tested and evaluated.Svante Arrhenius — in the 1890s he calculated th…

IPCC (Intergovernmental Panel on Climate Change)
Prediction
Droughts and heat waves
Wetter regions
Temperature changes
Extreme weather

Part 1 of 6IPCC and the greenhouse effect

IPCC and the greenhouse effect

Svante Arrhenius

Svante Arrhenius in the 1890s he calculated that doubling atmospheric carbon dioxide would make the Earth's surface 5 °C warmer, seriously affecting the climate.
His predictions are coming true in the 21st century.

IPCC (Intergovernmental Panel on Climate Change)

IPCC (Intergovernmental Panel on Climate Change) it studies evidence from thousands of scientists worldwide and advises governments.
It states that global warming is happening because of human activities such as burning fossil fuels and deforestation,
- which raise carbon dioxide and other greenhouse gases.

Prediction

Prediction by the middle of the 21st century global temperatures will rise by another 1.3-1.8 °C.

Part 2 of 6Predicted impacts

Sea level

Sea level as oceans warm and land ice melts, some scientists predict a rise of between 26 and 82 cm by the end of the 21st century.
Low-lying countries such as Tuvalu, and areas of many other countries, will disappear beneath the sea.

Droughts and heat waves

Droughts and heat waves as temperatures rise and rainfall patterns change, huge areas will become infertile and dry and arid land will expand.
Species will die out where there is no water, people will starve and fires will destroy whole ecosystems.

Wetter regions

Wetter regions many parts will get more rain and snow than ever before, often as extreme storms or blizzards.
This will cause floods that wash away fertile soil and cause loss of homes and lives.

Temperature changes

Temperature changes some countries will get hotter and others colder.
Warmer places will support pests such as mosquitoes, ticks and crop pests, affecting health and agriculture.
Plant life, animal migration patterns and local species will change, and many species will become extinct.

Extreme weather

Extreme weather hurricanes and storms will happen more often, and a single storm can badly damage power supplies, buildings, roads and railways.

Hope

Hope only a third of the predicted temperature rise for the next half century will happen for certain,
so changing how we live may stop climate change before it cannot be undone.

Part 3 of 6What a climate model is

Climate model

Climate model a computer program that uses mathematical equations to represent the processes that control the climate.

Grid

Grid the Earth is divided into a three-dimensional grid of boxes covering atmosphere, ocean, land and ice.
For each box the model calculates temperature, pressure, humidity, wind and other quantities,
- and how energy and water move between neighbouring boxes through time.

Computing

Computing there are billions of calculations, so very powerful supercomputers are needed.

Part 4 of 6Inputs and outputs

Inputs

Inputs energy from the Sun, greenhouse gas concentrations, aerosols from volcanoes and pollution, land use and ocean currents.

Scenarios

Scenarios scientists run the model with different assumptions about future emissions, such as emissions that keep rising or fall sharply by 2050.

Outputs

Outputs predicted temperature, rainfall, sea level and ice cover for each region over coming decades.

Part 5 of 6Testing the model

Hindcasting

Hindcasting the model is started at a past date, such as 1900, to see whether it reproduces the known temperature record up to the present.
Models with both natural and human factors match observed warming well, while models with only natural factors do not.

Comparison

Comparison many independently built models giving similar predictions increases confidence.

Part 6 of 6Strengths and limitations

Strengths	Limitations
Can test what might happen without risk or cost	The climate is very complex; some processes, such as clouds, are hard to represent
Can test different future scenarios	The future depends on human choices that are unknown
Improve as data and computers improve	Grid boxes are large, so small-scale detail is missing

Uncertainty

Uncertainty predictions are given as a range, such as 1.5 to 4.5 °C of warming by 2100 depending on the scenario.

Uses

Uses governments plan sea defences, farming and energy supply and set emission targets.

Weather forecasts

Weather forecasts they use similar models but are reliable for only a few days, while climate models predict long-term averages.

Key terms

Term	Meaning
IPCC	The Intergovernmental Panel on Climate Change, which advises governments.
Climate model	A computer program that represents the processes controlling climate.
Scenario	An assumption about future emissions used to run a model.
Hindcasting	Testing a model by checking whether it reproduces past records.
Arid	Very dry with little rainfall.
Extinct	No longer existing as a species.

Avoid these mistakes

Saying models are wrong because they cannot predict the weather next week.

Treating a model prediction as a certain fact.

Confusing a model with a real experiment.

Forgetting that the inputs strongly affect the output.

?What do you want to solve now?

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Last updated: 13 October 2026